Lesson topic: Free fall. The movement of a body thrown vertically upwards.
Lesson Objectives: to give students an idea of the free fall and motion of a body thrown vertically upwards, as a special case of uniformly accelerated motion, in which the modulus of the acceleration vector is a constant value for all bodies. The education of attentiveness, accuracy, discipline, perseverance. Development of cognitive interests, thinking.
Lesson type: combined lesson.
Demos: 1. Falling bodies in air and rarefied space. 2. Movement of a body thrown vertically upwards.
Equipment: 1.5m long glass tube, various bodies, board.
Knowledge check: independent work on the topic "Newton's Laws".
During the classes:
1. Organizational moment. (1 min)
2. Checking knowledge. (15 minutes)
3. Presentation of new material. (15 minutes)
A) free fall. Acceleration of gravity.
B) Dependence of the speed and coordinates of the falling body on time.
D) Dependence of the speed and coordinates of a body thrown vertically upwards on time.
4. Consolidation of new material. (7 min)
5. Homework. (1 min)
6. The result of the lesson. (1 min)
Lesson summary:
1. Greeting. Checking those present. Familiarization with the topic of the lesson and its objectives. Students write the date and topic of the lesson in their notebooks.
2. Independent work on the topic "Newton's Laws".
3. All of you have repeatedly observed the fall of bodies in the air and threw objects up yourself. The great scientist of antiquity, Aristotle, based on observations, built a theory according to which the heavier the body, the faster it falls. This theory has existed for two thousand years - after all, the stone really falls faster than the flower. Let's take two bodies, light and heavy, tie them together and throw them from a height. If a light body always falls more slowly than a heavy one, then it must slow down the fall of a heavy body, and therefore a bunch of two bodies must fall more slowly than one heavy body. But after all, the bundle can be considered one body, heavier, and, therefore, the bundle must fall faster than one heavy body.
Having discovered this contradiction, Galileo decided to test by experience how balls of different weights would actually fall: let nature itself give the answer. He made balls and dropped them from the Leaning Tower of Pisa - both balls fell almost simultaneously. Galileo made an important discovery: if air resistance can be neglected, then all falling bodies move uniformly accelerated with one acceleration.
Free fall is the movement of bodies under the influence of gravity (i.e., in conditions where air resistance can be neglected).
Students have no doubt that the free fall of a body is an accelerated movement. However, whether this movement is uniformly accelerated, they find it difficult to answer. The answer to this question can be given by experiment. If you take a series of snapshots of a falling ball at certain intervals (stroboscopic photo), then by the distances between successive positions of the ball, you can determine that the movement is really uniformly accelerated without an initial speed (textbook p. 53, Fig. 27).
Let's do an experiment. Let's take a glass tube with bodies and turn it over sharply. We see that heavier bodies fell faster. Then we pump out the air from the tube and conduct the experiment again. It can be seen that all bodies fall at the same time.
If we consider the fall of a heavy small ball in the air, then the force of air resistance can be neglected, because. the resultant of the forces of gravity and resistance differs little from the force of gravity. Therefore, the ball moves with an acceleration close to the acceleration of free fall.
If we consider the fall of a piece of cotton wool in the air, then such a movement cannot be considered free, because. drag is a significant part of the force of gravity.
So a=g=const= 9.8 m/s2. It should be noted that the gravitational acceleration vector is always directed downward.
The concept of free fall has a broad meaning: a body falls freely not only when its initial velocity is zero. If a body is thrown with an initial velocity, then it will also fall freely. Moreover, free fall is not only downward movement. If a body in free fall will fly up for some time, reducing its speed, and only then begins to fall.
Let's complete the following table together:
B) If we combine the origin of coordinates with the initial positions of the body and direct OY downward, then the graphs of the dependence of the speed and coordinates of the falling body on time will look like: Т.О. in free fall, the speed of a body increases by about 10 m/s every second.
C) Consider the cases when the body is thrown upwards. Let's match the origin of coordinates with the initial position of the body and direct OY vertically upwards. Then the projections of velocity and displacement at the origin will be positive. The figures show graphs for a body thrown at a speed of 30 m/s.
4. Questions:
1) Will the time of free fall of different bodies from the same height be the same?
2) What is the free fall acceleration? Units?
3) What is the acceleration of a body thrown vertically upward at the top of the trajectory? What about speed?
4) Two bodies fall from one point without an initial velocity with a time interval t. How do these bodies move in flight relative to each other?
Tasks: 1) The stone fell from one rock for 2 s, and from the other 6 s. How many times higher is the second rock than the first?
In order to find how many times one rock is higher than another, you need to calculate their heights (y = g t2/ 2), and then find their ratio. Answer: 9 times
2) A body falls freely from a height of 80 m. What is its displacement at the last second? Let's take the height h=80 m for the time t, the height h1 for the time t-1. ∆ h=h-h1 From the equation h = g t2/ 2 we find the time t if h1 = g (t - 1) 2/ 2 Answer: 35 m.
5. Today in the lesson we considered a special case of uniformly accelerated motion - free fall and the motion of a body thrown vertically upwards. We found out that the module of the acceleration vector is a constant value for all bodies, and its vector is always directed downwards. We considered the dependence of the speed and coordinates on time of a falling body and a body thrown vertically upwards.
INDEPENDENT WORK ON THE TOPIC NEWTON'S LAWS.
FIRST LEVEL.
1. A body with a mass of 2 kg moves with an acceleration of 0.5 m / s2. What is the resultant of all forces? A. 4 N B. 0 C. 1 N
2. How would the Moon begin to move if it were affected by the gravitational force of the Earth and other bodies?
A. Uniformly and rectilinearly tangential to the original trajectory of movement.
B. Rectilinear towards the Earth.
B. Moving away from the Earth in a spiral.
MIDDLE LEVEL.
1.A) There is a bar on the table. What forces are acting on it? Why is the block at rest? Draw forces graphically.
B) What force imparts an acceleration of 4 m/s2 to a body of mass 5 kg?
C) Two boys pull a cord in opposite directions, each with a force of 200 N. Will the cord break if it can withstand a load of 300 N?
2.A) What will happen to the bar and why, if the trolley on which it stands is sharply pulled forward? Stop abruptly?
B) Determine the force under which a body of mass 500 g moves with an acceleration of 2 m / s2
C) What can be said about the acceleration that the Earth receives when interacting with a person walking on it. Justify your answer.
ENOUGH LEVEL.
1.A) With the help of two identical balloons, different bodies are lifted from rest. On what basis can you conclude which body has a large mass?
B) Under the action of a force of 150 N, the body moves in a straight line so that its coordinate changes according to the law x = 100 + 5t + 0.5t2. What is the body weight?
C) An incomplete glass of water is balanced on a balance. Will the balance of the balance be disturbed if a pencil is immersed in water and held in the hand without touching the glass?
2.A) The fox, running away from the dog, is often saved by making sharp sudden movements to the side when the dog is ready to grab it. Why does the dog miss?
B) A skier weighing 60 kg, having a speed at the end of the descent of 10 m/s, stopped 40 s after the end of the descent. Determine the modulus of the force of resistance to movement.
Q) Is it possible to sail on a sailboat, directing the air flow from a powerful fan located on the boat? What happens if you blow past the sail?
HIGH LEVEL.
1.A) The frame of reference is connected with the car. Will it be inertial if the car is moving:
1) uniformly rectilinearly along a horizontal highway; 2) accelerated along a horizontal highway; 3) evenly turning; 4) evenly uphill; 5) evenly from the mountain; 6) accelerated from the mountain.
B) A body at rest with a mass of 400 g under the action of a force of 8 N acquired a speed of 36 km / h. Find the path that the body has traveled.
c) A horse is pulling a loaded cart. According to Newton's third law, the force with which the horse pulls the cart = the force with which the cart pulls the horse. Why does the cart follow the horse?
2.A) The car moves uniformly along the ring road. Is the frame of reference associated with it inertial?
B) A body with a mass of 400 g, moving in a straight line with an initial speed, acquired a speed of 10 m/s in 5 s under the action of a force of 0.6 N. Find the initial speed of the body.
C) A rope is thrown over an immovable block. At one end, holding on with his hands, a person hangs, and at the other, a load. The weight of the load = the weight of the person. What happens if a person pulls himself up the rope on his hands?
Demonstration: Draw a small circle on the floor. Passing with the ball in hand next to him, you need to unclench your fingers on the move so that the ball hits the circle (the addition of two "natural" movements). Why is this not easy to do?
Questions:
1. How can you determine whether a given body is in an inertial or non-inertial frame of reference?
2. It is known that a body moving freely on a horizontal surface gradually slows down and eventually stops. Doesn't this experimental fact contradict the law of inertia?
3. Give the largest number of examples of the manifestation of inertia.
4. How to explain the lowering of the mercury column when shaking a medical thermometer?
5. A train moving along a straight horizontal track is affected by a constant traction force of a diesel locomotive equal to the resistance force. What movement does the train make? How does the law of inertia manifest itself in this case?
6. Is it possible to see from a balloon how the globe rotates under us?
7. How to jump from a moving car?
8. If the windows in the compartment are closed, then by what signs do you judge that the train is moving?
9. Is it possible to establish, by observing the movement of the Sun during the day (day), whether the frame of reference associated with the Earth is inertial?
IV. § 19. Questions to § 19.
Compile a summary table "Inertia" using figures, drawings and textual material.
The amount of matter (mass) is a measure of it, established in proportion to its density and volume ...
I. Newton
Lesson 23/3. ACCELERATION OF BODIES DURING INTERACTION. WEIGHT.
The purpose of the lesson: introduce and develop the concept of "mass".
Lesson type: combined.
Equipment: centrifugal machine, steel and aluminum cylinders, demonstration ruler, TsDZM device, interaction demonstration device, 2 kg weight, universal tripod, thread.
Lesson plan:
2. Poll 10 min.
3. Explanation 20 min.
4. Fixing 10 min.
5. Homework 2-3 min.
II. The poll is fundamental: 1. Inertial frames of reference. 2. Newton's first law.
Questions:
1. A boy holds a balloon filled with hydrogen on a string. What forces acting on the ball cancel each other out if it is at rest?
2. Explain the action of which bodies is compensated in the following cases: a) the submarine is in the water column; b) the submarine lies on a hard bottom.
3. The body is at rest in a given IFR, and what movement does it make in any other IFR?
4. In what case can the frame of reference associated with the car be considered inertial?
5. In what frame of reference is Newton's first law fulfilled?
6. How can you be sure that this body does not interact with other bodies?
7. How do experienced drivers save fuel using the phenomenon of inertia?
8. Why, being in a train compartment with a curtained window and good sound insulation, can you find that the train is moving at an accelerated rate, but you cannot know that it is moving evenly?
9. Once Baron Munchausen, bogged down in a swamp, pulled himself out by his hair. Did he thereby violate Newton's first law?
III. Under what conditions is the body moving with acceleration? Demonstration.
Conclusion . The reason for the change in body speed (acceleration) is the uncompensated impact (influence) of other bodies. Examples: free fall of a ball, the action of a magnet on a steel ball at rest and in motion.
Interaction - the action of bodies on each other, leading to a change in the state of their motion . Demonstration with a device to demonstrate the interaction.
The interaction of two bodies not affected by any other bodies is the most fundamental and simplest phenomenon that we can study. Demonstration of the interaction of two carts (two carriages on an air cushion).
Conclusion: When interacting, both bodies change their speed, and their accelerations are directed in opposite directions.
What else can be said about the accelerations of carts during their interaction?
It turns out that the acceleration of the body is the smaller, the greater the mass of the body and vice versa (demonstration).
m 1 a 1 = m 2 a 2
Measurement of the mass of interacting bodies. Weight standard (cylinder made of an alloy of platinum and iridium) 1 kg. A standard mass of 1 kg can be obtained by taking 1 liter of water at 4°C and normal atmospheric pressure. And how to measure the mass of an individual body?
m e a e \u003d ma.
Definition: Weight (m) – the property of a body to counteract a change in its speed, measured by the ratio of the acceleration modulus of the mass standard to the acceleration modulus of the body during their interaction.
Interaction of steel and aluminum cylinders (demonstration).
What will this ratio be for two aluminum cylinders?
Other ways to measure masses: 1. m = ρ·V (for homogeneous bodies). 2. Weighing. Is it possible to measure the mass of the planet by weighing; molecules; electron?
Student Conclusions:
1. In C, mass is measured in kilograms.
2. Mass is a scalar quantity.
3. Mass has the property of additivity.
A deeper meaning of mass in SRT. Relationship between body mass and rest energy: E = mc 2 . The mass of matter is discrete. mass spectrum. The nature of mass is one of the most important and yet unsolved problems of physics.
IV.Tasks:
1. Boys with masses of 60 and 40 kg, holding hands, turn around a certain point so that the distance between them is 120 cm. On a circle of what radius does each of them move?
2. Compare the accelerations of two steel balls during the collision if the radius of the first ball is twice the radius of the second. Does the answer to the problem depend on the initial velocities of the balls?
3. Two boys on skates, pushing off each other with their hands, went in different directions with speeds of 5 and 3 m/s. Which boy's mass is greater and by how many times?
4. At what distance from the center of the Earth is the point around which the Earth and the Moon revolve, if the mass of the Earth is 81 times the mass of the Moon, and the average distance between their centers is 365,000 km.
Questions:
1. With the help of two identical balloons, different bodies are lifted from rest. On what basis can one conclude which of these bodies has a greater mass?
2. Why in hockey are the defenders chosen more massive and the forwards lighter?
3. Why is it difficult for a firefighter to hold a hose from which water is beating?
4. What is the importance of webbed feet in waterfowl?
5. What is the reason for the acceleration of the following bodies: 1) an artificial satellite as it moves around the Earth; 2) an artificial satellite during its deceleration in dense layers of the atmosphere; 3) a bar sliding down an inclined plane; 4) a free-falling brick?
V. § 20-21 Ex. 9, nos. 1-3. Ex. 10, no. 1, 2.
1. Make a generalizing table "mass" using pictures, drawings and textual material.
2. Suggest several options for the design of devices that can be used to compare the masses of bodies during interaction.
3. Place a glass of water on a sheet of paper at the edge of the table. Pull the sheet sharply in a horizontal direction. What will happen? Why? Explain the experience.
4. A rope is thrown over a fixed block. A person hangs on one end of the rope, holding on with his hands, and a load on the other. The weight of the load is equal to the weight of the person. What happens if a person pulls himself up on a rope on his hands?
... an applied force is an action performed on a body in order to change its state of rest or uniform rectilinear motion.
I. Newton
Lesson 24/4. FORCE
The purpose of the lesson: develop the concept of "force" and choose a unit of force.
Lesson type: combined.
Equipment: device "Bodies of unequal mass", centrifugal machine, tripod, load, spring.
Lesson plan: 1. Introductory part 1-2 min.
2. Survey 15 min.
3. Explanation 15 min.
4. Fixing 10 min.
5. Homework 2-3 min.
II. Poll fundamental: 1. Inertness of bodies. 2. Mass of bodies.
Tasks:
1. A wagon weighing 60 tons approaches a fixed platform at a speed of 0.2 m/s and hits with buffers, after which the platform receives a speed of 0.4 m/s. What is the mass of the platform if, after the impact, the speed of the car decreased to 0.1 m/s?
2. Two bodies with masses of 400 and 600 g moved towards each other and stopped after the impact. What is the speed of the second body if the first was moving at a speed of 3 m/s?
3. Experimental task: Determine the ratio of the masses of the bodies in the "Bodies of unequal mass" device.
Questions:
1. Suggest a way to measure the mass of the moon.
2. Why is an ax leaned behind when driving a nail into thin plywood?
3. Why is it difficult to walk on loose snow (sand)?
4. The Eiffel Tower has a height of 300 m and a mass of 9000 tons. What mass will its exact copy 30 cm high have?
5. Electric coffee grinder is a closed cylinder with an electric motor. How to determine the direction of rotation of the armature of this electric motor, if the coffee grinder window is closed and it cannot be disassembled?
III. Interaction of two bodies. As a result of the interaction of the body, accelerations are obtained, and: . This is a very good formula. With its help, you can determine the mass of the second body, if the mass of the first body is known, we will transform this formula: a 1 = a 2 . It follows from it that in order to calculate the acceleration of the first body, it is necessary to know the mass m 1 , and 2 and m2. Projectile flight example. What bodies act on the projectile during flight? Earth? Air? Air resistance can be neglected. What does an artilleryman need to know in order to calculate the acceleration of a projectile?
Or = = .
Is it possible to measure the influence of the second body (Earth) on the first body (projectile)? The influence of one body on another is briefly called force ().
The text of the work is placed without images and formulas.
The full version of the work is available in the "Job Files" tab in PDF format
Introduction
Relevance
Are you familiar with the situation when, after a birthday or some other holiday, a lot of balloons appear in the house? At first, the children are happy with the balls, they play with them, but soon they stop paying attention to them and the balls only get under their feet. What to do with them so that they do not lie without any purpose, but bring benefits? Of course, use in cognitive activities!
In general, balloons are an excellent material for demonstrating various experiments and models. It would be interesting to write a book in which all physical concepts will be explained through them. In the meantime, I want to invite you to conduct more than a dozen experiments from different fields of science - from thermodynamics to cosmology - in which the props are common: balloons.
Target: Explore balloons as an invaluable material at hand for observing physical phenomena and staging various physical experiments.
Tasks:
Learn about the history of balloons.
Set up a series of experiments with balloons.
Analyze the observed phenomena and formulate conclusions.
Create a multimedia presentation.
Object of study: balloon.
Research methods:
. Theoretical: study of literature on the research topic.
. Comparative-comparative.
. Empirical: observation, measurement.
. Experimental-theoretical : experiment, laboratory experiment.
material of this study are Internet sources, teaching aids in physics, physics textbooks, problem books, archive data and other reference literature.
Practical significance: The results of the study can be used in physics lessons, conferences, elective courses and extracurricular activities.
Theoretical part
The history of the creation of balloons
Looking at modern balloons, many people think that this bright, pleasant toy has become available only recently. Some, more knowledgeable, believe that balloons appeared somewhere in the middle of the last century, simultaneously with the beginning of the technical revolution. Actually it is not. The history of balloons filled with air began much earlier. Only the ancestors of our balls looked completely different from what they are now. The first references to the manufacture of balloons flying in the air that have come down to us are found in Karelian manuscripts. They describe the creation of such a ball, made from the skin of a whale and a bull. And chronicles of the 12th century tell us that in the Karelian settlements almost every family had a balloon. Moreover, it was with the help of such balls that the ancient Karelians partially solved the problem of off-road - the balls helped people overcome the distances between settlements. But such journeys were quite dangerous: the shell of animal skins could not withstand air pressure for a long time - that is, in other words, these balloons were explosive. And so, in the end, only legends remained of them. But less than 7 centuries have passed since that semi-mythical era, when rubber balloons were invented in London by Professor Michael Faraday. The scientist studied the elastic properties of rubber - and built two "cakes" from this material. In order for the "cakes" not to stick together, Faraday treated their inner sides with flour. And after that, with his fingers, he glued their raw, remaining sticky edges. The result was something like a bag that could be used for experiments with hydrogen. About 80 years after that, the scientific hydrogen bag turned into a popular pastime: rubber balls were widely used in Europe during city holidays. Due to the gas that filled them, they could rise up - and this was very popular with the public, which had not yet been spoiled by either air flights or other miracles of technology. But these balloons were somewhat similar to their legendary predecessors: they used hydrogen (and, as you know, it is an explosive gas). But, nevertheless, everyone got used to hydrogen - fortunately, there were no special troubles from balloons with this gas until 1922. Then in the USA, at one of the city holidays, a joker blew up the decoration of the holiday for fun - that is, balloons. As a result of this explosion, an official was injured, and therefore law enforcement agencies reacted quite quickly. Fun that turned out to be dangerous enough
finally stopped by banning filling balloons with hydrogen. Nobody suffered from this decision - the place of hydrogen in the balloons was instantly taken by much safer helium. This new gas lifted the balloons just as well as hydrogen did. In 1931, Neil Tylotson released the first modern, latex balloon (polymer latex is obtained from aqueous dispersions of rubber). And since then, balloons have finally been able to change! Before that, they could only be round - and with the advent of latex, for the first time, it became possible to create long, narrow balls. This innovation immediately found application: holiday designers began to create compositions from balloons in the form of dogs, giraffes, airplanes, hats ... Neil Tylotson's company sold through the mail millions of balloon sets designed to create funny figures. The quality of balloons at that time was far from the same as now: when inflated, the balloons lost some of their brightness, they were fragile and quickly burst. Therefore, balloons slowly lost their popularity - the fact that they can fly in the air did not seem so wonderful and interesting in the twentieth century. Therefore, long before the end of the 20th century, balloons began to be bought up only for city and children's holidays. But the inventors did not forget about balloons, they worked to improve them. And the situation has changed. Now the industry produces such balloons that do not lose color when inflated - and in addition they have become much more durable and durable. Therefore, now balloons have again become very popular - designers are willing to use them when decorating various holidays, concerts, presentations. Weddings, birthdays, citywide celebrations, PR campaigns, shows… - updated, bright balloons are everywhere in place. Here is such an interesting, long-standing history of a simple fun we have known since childhood.
Practical part
Experiment #1
Qualitative comparison of the densities of water - hot, cold and salty
If you investigate liquids that do not mix and do not enter into a chemical reaction, then it is enough just to pour them into one transparent vessel, for example, a test tube. The density can be judged by the arrangement of the layers: the lower the layer, the higher the density. Another thing is if the liquids are mixed, such as hot, cold and salt water.
We compare the behavior of balloons filled with hot, cold, and salted water in hot, cold, and salted water, respectively. As a result of the experiment, we can draw a conclusion about the densities of these liquids.
Equipment: three balls of different colors, a three-liter jar, cold, hot and salt water.
Experiment progress
Pour three portions of different water into balls - blue hot,
in green cold and in red salty water.
2. Pour hot water into the jar, put the balls there in turn (Appendix No. 1).
3. Pour cold water into the container, again place all the balls there in turn.
4.Pour salt water into the jar, observe the behavior of the balls.
Conclusion:
1. If the density of liquids is different, then a liquid with a lower density floats above a liquid with a higher density, that is
hot water< холодной воды < соленой воды
2. The greater the density of the liquid, the greater its buoyancy force:
F A=Vg; since V and g are constant F Adepends on the size.
Experiment #2
Slimming and fattening ball. The fact that various bodies and gases expand from heat and contract from cold can be easily demonstrated using the example of a balloon. In frosty weather, take a balloon with you for a walk and inflate it tightly there. If you then bring this ball into a warm house, then it will most likely burst. This will happen due to the fact that from the heat the air inside the ball will expand dramatically and the rubber will not withstand the pressure.
Equipment: balloon, tape measure, refrigerator, hot water pot
Experiment progress
Task number 1 1. Inflate a balloon in a warm room.
2. Using a centimeter tape, we measured its circumference (we got 80.6 cm).
3. After that, put the ball in the refrigerator for 20-30 minutes.
4. Again measured its circumference. We found that the ball "lost" almost a centimeter (in our experiment, it became 79.7 cm). This happened due to the fact that the air inside the balloon was compressed and began to occupy a smaller volume.
Task number 2
1 With the help of a centimeter tape, we measured the circumference of the balloon (we got 80.6 cm).
2. Put the ball in a bowl and pour hot water from a jar over it.
3. We measure the new volume of the ball. We found that the ball "thickened" by almost a centimeter (in our experiment it became 82 cm). This happened due to the fact that the air inside the balloon expanded and began to occupy a larger volume.
Conclusion: the air contained in the balloon contracts when cooled, and expands when heated, which proves the presence of thermal expansion. Gas pressure depends on temperature. When the temperature decreases, the air pressure in the ball decreases, i.e. the volume of the ball decreases. With an increase in temperature, the air pressure in the ball increases, which proves the dependence of the volume and pressure of gases on temperature.
Experiment #3
"Ball in the Bank"
Equipment: ball, three-liter jar, hot water.
The progress of the experiment.
1. Pour water into the balloon so that it does not pass into the neck of the jar.
2. Pour hot water into a jar, chat and pour it out. Leave the jar for 5 minutes.
3. We put a ball filled with water on a jar. We are waiting 20 minutes. The ball falls into the jar
Conclusion: since the ball, filled with water and larger in diameter than the neck of the jar, fell inward, it means that there is a pressure difference: warm air inside the jar has a lower density than atmospheric air, the pressure inside is less; therefore, more atmospheric pressure encourages the ball to penetrate the can.
Experiment #4
"Air Paradox"
This experience confuses many.
Equipment: two identical balloons, a tube 10-30 cm long and 15-20 mm in diameter (the ball should be tightly put on it). two balloons, differently inflated, plastic tube, stand.
The progress of the experiment.
1. Slightly and NOT EQUALLY inflate the balls.
2. We stretch the balls on opposite ends of the tube. To prevent the balls from being blown away, we twist their necks.
3. We open the necks for free communication of air between the balls.
observation. Air flows from one balloon to another. But ... a small balloon inflates a big one!
Explanation. Many believe that since the mass of air is greater in a larger balloon, then this balloon will deflate and inflate a small balloon. But such reasoning is erroneous. The reason for the observed phenomenon is the pressure inside the ball. (Recall communicating vessels - water flows not from the vessel where there is less water, but from the one where the pressure is greater.) In addition, everyone knows how difficult it is to start inflating a balloon, but when the “dead” point is overcome, then it inflates easily. Therefore, the elasticity of rubber plays an important role.
Conclusion: The pressure of the gas inside the sphere is the greater, the smaller its radius.
Experiment #5
Ball - yoga
We are so accustomed to the fact that an inflated balloon, hitting the tip, bursts with noise,
that a ball on nails under the weight of a load is perceived by us as a supernatural phenomenon. Nevertheless, this is a fact.
Equipment: a board with nails, a balloon, a board, a weight, two tripods.
The progress of the experiment.
1. Put a balloon on a board with nails and press it with your hand from above.
2. We press on the ball with a previously measured load.
3. We observe the behavior of the ball.
Observations: the ball remains intact. And it's all about the footprint! The more nails, the more points of support for the body (i.e. more surface area on which the body rests). And all the force is distributed over all the nails in such a way that there is too little force on a single nail to pierce the ball.
Conclusion: pressure is distributed evenly over the entire surface of the ball, and up to a certain point this pressure is harmless for the ball.
Experiment #6
Electrostatic field indicator
Information. It is convenient to study electrostatic fields with the help of indicators that allow one to estimate the direction and magnitude of the Coulomb force at each point of the field. The simplest point indicator is a light conducting body suspended on a thread. Previously, it was recommended to use the core of an elder branch to make a light ball. At present, it is advisable to replace elderberry with foam plastic. Other solutions to the problem are also possible.
Exercise. Design and manufacture the simplest indicator of the electrostatic field. Experimentally determine its sensitivity.
The progress of the experiment.
1. From a piece of rubber from a children's balloon we blow out a rubber ball 1 with a diameter of 1-2 cm. Tie the ball to a silk thread 2 , which is reinforced to a rubber stopper.
2. We rub the surface of the ball to a characteristic metallic sheen with graphite powder from the lead of a soft simple pencil.
3. The ball was loaded from an ebonite stick worn with fur.
4. Enter the indicator in the field of a spherical charge and evaluate the sensitivity of the indicator by the magnitude of the acting force.
Conclusion: a small rubber ball covered with a conductor is a point indicator of the electric field.
Experiment #7
Ball and boat
Equipment: paper boat, metal plastic cover,
vessel with water.
The progress of the experiment.
1. We make a paper boat and put it on the water.
2. We electrify the ball and bring it to the boat.
observation. The ship will follow the ball.
3. We lower the metal cover into the water.
4. We electrify the ball and bring it to the lid without touching it.
observation. The metal cover floats towards the ball.
5. We lower the plastic cover into the water.
6. We electrify the ball and bring it to the lid without touching it.
observation. The heavy lid floats behind the ball.
Conclusion: In the electric field of the ball, paper and plastic are polarized and attracted to the ball. A charge is also induced in the metal cover. Since the friction force on the water is negligible, the boats easily set in motion.
Experiment #8
jumpers
Equipment: balloon, finely cut metal foil, cardboard sheet.
The progress of the experiment.
1. Pour finely chopped metal foil onto a sheet of cardboard.
2. We electrify the ball and bring it to the foil, but do not touch it.
observation. Sequins behave like living jumping grasshoppers. They jump, touch the ball and immediately fly off to the side.
Conclusion: Metallic sequins are electrified in the field of the ball, but at the same time remain neutral. The sequins are attracted to the ball, bounce, charge when touched and bounce as if they were charged with the same name.
Experiment #9
Air kiss according to Bernoulli's law
Equipment: 2 balloons, 2 threads 1 m long.
The progress of the experiment.
1. We inflate the balls to the same size and tie a thread to each.
2. We take the balls by the thread with the right and left hands so that they hang at the same level at some distance from each other.
3. Without touching the balls with your hands, try to connect them.
Explanation. From Bernoulli's law it follows that the pressure in the air stream is lower than atmospheric pressure. The force of atmospheric pressure from the sides will bring the balls together.
Experiment #10
Thermal strength test
Equipment: ball and candle
The progress of the experiment.
Pour water into the ball and bring the ball of water into the flame of the candle.
observation. The rubber is just smoky.
Explanation. The temperature of the shell, as long as there is water in it, will not rise above 100 °C, i.e. will not reach the combustion temperature of the rubber.
Experiment #11
How do the lungs work?
Equipment: plastic bottle, balloon number 1, balloon number 2 (I used a plastic bag instead), scotch tape.
The progress of the experiment.
1. Cut off the bottom of the plastic bottle
2. We place the balloon inside the bottle and pull it over the neck.
3. Tighten the cut off part with a fly from another balloon (or a plastic bag) and secure with tape.
4. We pull the film - the ball is inflated, we press on the film - the ball is deflated.
Explanation. The volume of air inside the bottle is isolated. When the film is pulled back, this volume increases, the pressure decreases and becomes less than atmospheric. The balloon inside the bottle is inflated with atmospheric air. When pressing on the film, the volume of air in the bottle decreases, the pressure becomes greater than atmospheric pressure, and the balloon is deflated. Our lungs do the same.
Experiment #12
Balloon as a jet engine
Equipment: balloon, straw, stationery gum, adhesive tape, car.
The progress of the experiment.
1. The balloon must be fixed at one end of the tube with a rubber band.
2. The second end of the tube must be fixed on the body of the machine with adhesive tape so that it is possible to inflate the ball through the tube.
3. The model is ready, you can run! To do this, you need to inflate the balloon through the tube, pinch the opening of the tube with your finger and put the machine on the floor. As soon as you open the hole, the air from the balloon will fly out and push the car. -12-
Explanation. This visual model demonstrates how jet engines work. The principle of its operation is that the jet of air escaping from the balloon, after it has been inflated and released, pushes the machine in the opposite direction.
3.Conclusion
On balloons, you can study the laws of pressure of bodies and gases, thermal expansion (compression), thermal conductivity, density of liquids and gases, Archimedes' law; electrification of bodies, it is even possible to construct instruments for measuring and studying physical processes.
The experiments carried out in this research work prove that the ball is an excellent tool for studying physical phenomena and laws. You can use this work at school in the classroom when studying the sections "Initial information about the structure of matter", "Jet propulsion", "Pressure of solids, liquids and gases", "Thermal and electrical phenomena". The collected historical material is applicable in the classroom in physics and extracurricular activities.
A computer presentation created on the basis of the practical part will help schoolchildren to quickly understand the essence of the physical phenomena being studied, and will cause a great desire to conduct experiments using the simplest equipment.
Obviously, our work contributes to the formation of genuine interest in the study of physics.
4.Literature
www.demaholding.ru
[Electronic resource]. Access mode: www.genon.ru
[Electronic resource]. Access mode: www.brav-o.ru
[Electronic resource]. Access mode: www.vashprazdnik.com
[Electronic resource]. Access mode: www.aerostat.biz
[Electronic resource]. Access mode: www.sims.ru
Turkina G. Physics on balloons. // Physics. 2008. No. 16.
MOU secondary school No. 5
Multi-level independent work in physics.
Grade 9
City of Zheleznodorozhny. 2011
FIRST LEVEL - the level of mandatory minimum training. Successful completion of tasks at this level indicates the compliance of this student with the state requirements of the standard for the course of physics in grades 7 and 8. They are required by all students. At this level, the student should be able to solve problems using 1 basic formula.
SECOND LEVEL - somewhat difficult level.
It is focused mainly on the achievement by students of the required level of training in physics. Along with tasks aimed at developing basic skills, it contains simple tasks that require ingenuity and ingenuity.
Tasks of this level make it possible to reveal the ability of students to apply knowledge according to the model, to solve calculation problems according to a rule or algorithm using 1-2 basic formulas.
THIRD LEVEL - elevated level.
It is designed for students with a good background in physics, which gives them the opportunity to quite intensively master the basic knowledge and skills and learn how to apply them in a variety of complicated situations.
Tasks of this level make it possible to reveal the ability of students to apply knowledge in a changed, non-standard situation, to solve calculation problems using more than 2 basic formulas.
"Material point. Trajectory, path, movement.
First level .
No. 1. In which of the following cases can a body be considered a material point?
A. The moon revolves around the earth.
B. The spacecraft makes a soft landing on the Moon.
Q. Astronomers observe an eclipse of the moon.
No. 2. The girl threw the ball up and caught it. Assuming that the ball has risen to a height of 2 m, find the modulus of the ball's displacement.
A. 2 m.
B. 4 m.
V. 0 m.
No. 3. Indicate what is taken as the body of reference when they say that the conductor is walking along the car at a speed of 3 km / h.
No. 4. According to a given trajectory of the body
find its displacement,
If the starting point of the trajectory is A, and the end point is C.
Solve the problem graphically.
Second level.
№ 1. Does the trajectory of the body's motion depend on the frame of reference?
No. 2. The helicopter, flying in a horizontal flight in a straight line for 30 km, turned at an angle of 90 and flew another 40 km. Find the path and movement module of the helicopter.
No. 3. Draw schematically the trajectory of the movement of the points of the propeller of the aircraft relative to the pilot.
No. 4. The ball fell from a height of 4 m, bounced off the ground and was caught at half the height. What is the path and modulus of the ball.
Third level.
No. 1. Draw the trajectory of movement, in which the displacement module is 10 cm, and the path is 30 cm.
No. 2. The motorboat passed along the lake in the north-east direction for 2 km, and then in the northern direction for another 1 km. Find the module and the direction of movement by geometric construction.
№ 3. Give an example of movement, the trajectory of which in one frame of reference is a straight line, and in another - a circle.
No. 4. The tourist went from village A to village B. First, he walked 3 km to the north, then turned west and walked another 3 km, and the last kilometer he moved along a country road going north. What path did the tourist travel and what is his module of movement? Draw a trajectory of movement.
Independent work on the topic
"Rectilinear Uniform Motion".
First level.
No. 1. A train 240 m long, moving uniformly, passed the bridge in 2 minutes. What is the speed of the train if the bridge is 360 m long?
No. 2. The car traveled 900 m in the first 10 minutes. What distance will it cover in 0.5 hours, moving at the same speed?
Second level.
No. 1. When moving along the OX axis, the coordinate of the point changed in 5 s from the value x 1 \u003d 10 m to the value x 2 \u003d - 10 m. Find the velocity module of the point and the projection of the velocity vector on the OX axis. Write down the dependence formula x( t ). Consider the speed constant.
No. 2. Two bodies move along the OX axis, the coordinates of which change according to the formulas: x 1 \u003d 10 +2 t and x 2 \u003d 4 + 5 t . How do these bodies move? At what point in time will the bodies meet? Find the coordinate of the meeting point.
Third level.
No. 1. The movement of a material point in the XOY plane is described by the equations x=2 t , y=4-2 t . Find the starting coordinates of the moving point. Build a trajectory.
No. 2. The distance between two piers is 10 minutes downstream and 30 minutes upstream. How long will it take for a lifebuoy that has fallen into the water to float downstream?
Independent work on the topic
"Rectilinear uniformly accelerated motion".
First level.
No. 1. With what acceleration does a tram starting off move if it picks up speed of 36 km / h in 25 s?
No. 2. The train, moving away from the station, picks up a speed of 15 m / s in 1 minute. What is its acceleration?
Second level.
No. 1. After 10 seconds, the car acquires a speed of 20 m / s. With what acceleration was the car moving? After what time will its speed become equal to 108 km/h if it moves with the same acceleration?
No. 2. The body moves with uniform acceleration. How long will it take to move in the same direction. What and at the initial moment, if 0x \u003d 20 m / s, and x \u003d -4 m / s 2?
Third level.
No. 1. The body moves in a straight line. At the beginning and at the end of the movement, the speed modulus is the same. Could the body move with constant acceleration?
No. 2. Two trains go towards each other: one will accelerate in the direction to the north; the other slows down in a southerly direction. How are train accelerations directed?
Independent work on the topic
"Displacement in rectilinear uniformly accelerated motion."
First level.
No. 1. A cyclist moving at a speed of 3 m/s starts downhill with an acceleration of 0.8 m/s 2 . Find the length of the mountain if the descent took 6 s.
No. 2. The car increased its speed from 36 km / h to 54 km / h in 4 s. How far did the car travel during this time?
Second level.
No. 1. The car, having stopped in front of a traffic light, then picks up a speed of 54 km / h on a path of 50 m. With what acceleration should it move? How long will the acceleration take?
No. 2. A bullet flying at a speed of 400 m / s hits an earthen rampart and penetrates it to a depth of 36 cm. How long did the bullet move inside the rampart? With what acceleration? What was its speed at a depth of 18 cm?
Third level.
No. 1. With uniformly accelerated movement, the point passes in the first two equal consecutive periods of time, 4 s each, the paths are 24 m and 64 m. Determine the initial speed and acceleration of the moving point.
No. 2. Having noticed the traffic inspector, the driver brakes sharply. The car passed point A at a speed of 144 km / h, and point B - already at a speed of 72 km / h. At what speed was the car moving in the middle of segment AB?
Independent work on the topic
"Newton's Laws".
Option 1.
First level.
No. 1. There is a bar on the table. What forces are acting on it? Why is the block at rest? Draw forces graphically.
No. 2. What force imparts an acceleration of 4 m / s 2 to a body weighing 5 kg?
No. 3. Two boys pull the cord in opposite directions, each with a force of 200N. Will the cord break if it can withstand a load of 300 N?
Second level.
No. 1. With the help of two identical balloons, different bodies are lifted from rest. On what basis can one conclude which of these bodies has a large mass?
No. 2. Under the action of a force of 150N, the body moves in a straight line so that its coordinate changes according to the law x \u003d 100 + 5 t +0.5 t2 . What is the body weight?
No. 3. An incomplete glass of water is balanced on the scales. Will the balance of the balance be disturbed if a pencil is immersed in water and held in the hand without touching the glass?
Third level.
No. 1. The frame of reference is connected to the car. Will it be inertial if the car moves: 1) evenly and straight on a horizontal highway; 2) accelerated along a horizontal highway; 3) evenly turning; 4) evenly uphill; 5) evenly from the mountain; 6) accelerated from the mountain?
No. 2. A body at rest with a mass of 400 g under the action of a force of 8 N acquired a speed of 36 km / h. Find the path that the body has traveled.
No. 3. A horse pulls a loaded cart. According to Newton's third law, the force with which the horse pulls the cart is equal to the force with which the cart pulls the horse. Why does the cart follow the horse?
Independent work on the topic
"Newton's Laws".
Option 2.
First level.
No. 1. What will happen to the bar and why, if the trolley on which it stands is sharply pulled forward? Stop abruptly?
No. 2. Determine the force under the influence of which a body of mass 500 g receives an acceleration of 2 m / s.
№ 3. What can be said about the acceleration that the Earth receives when interacting with a person walking on it? Justify the answer.
Second level.
No. 1. A fox, running away from a dog chasing her, often saves herself by making sharp sudden movements to the side just at the moment when the dog is ready to grab her with her teeth. Why does the dog miss?
No. 2. A skier weighing 60 kg, having a speed of 10 m/s at the end of the descent from the mountain, stopped 40 s after the end of the descent. Determine the modulus of the force of resistance to movement.
No. 3. Is it possible to sail on a sailboat by directing air flow from a powerful fan on the boat to the sails? What happens if you blow past the sail?
Third level.
No. 1. The car moves uniformly along the ring road. Is the frame of reference associated with it inertial?
No. 2. A body weighing 400 g, moving in a straight line with a certain initial speed, acquired a speed of 10 m/s in 6 s under the action of a force of 0.6 N. Find the initial speed of the body.
No. 3. A rope is thrown over a fixed block. A person hangs on one end of the rope, holding on with his hands, and a load on the other. The weight of the load is equal to the weight of the person. What happens if a person pulls himself up the rope on his hands?
Independent work on the topic
"Free fall".
Option 1.
First level.
No. 1. A body falls without initial velocity. What is its speed after 2 seconds of fall?
№ 2. How long will it take the ball, which began its fall without initial speed, to cover a distance of 20 m?
Second level.
No. 1. How long did the body fall without initial speed, if in the last 2 s it has traveled 60 m?
No. 2. A body falls from a height of 100 m without initial velocity. What is the distance traveled by the body during the first and last seconds of its fall?
Third level.
No. 1. A body falls freely from a height of 27 m. Divide this height into three parts so that the passage of each of them takes the same time.
No. 2. Two loads were dropped from a helicopter without an initial speed, and the second one was 1 s later than the first. Determine the distance between the loads after 2 s and 4 s after the start of the movement of the first load.
Independent work on the topic
"Free fall".
Option 1.
First level.
No. 1. A ball was fired vertically upwards from a spring pistol, which rose to a height of 5 m. With what speed did the ball fly out of the pistol?
No. 2. The ball is thrown vertically upwards with a speed of 18 m/s. What movement did he make in 3 seconds?
Second level.
No. 1. The boy threw the ball vertically upwards and caught it after 2 s. What is the height of the ball and what is its initial speed?
No. 2. Throwing the ball vertically upwards, the boy tells him the speed is 1.5 times greater than the girl. How many times higher will the ball thrown by the boy rise?
Third level.
Two balls are thrown vertically upwards with an interval of 1 s. The initial speed of the first ball is 8 m/s, and the second - 5 m/s. At what height will they meet?
No. 2. Two balls are simultaneously thrown from a tower 20 m high: one is thrown up at a speed of 15 m/s, the other is thrown down at a speed of 5 m/s. What is the time interval separating the moments of their fall to the ground?
Independent work on the topic
"Gravity and free fall acceleration".
№ 1. What is the force of gravitational attraction between two identical billiard balls at the moment of collision? The mass of each ball is 200 g, the diameter is 4 cm.
№ 2. At what distance will the force of attraction between two bodies weighing 1000 kg each be equal to 6.6710 -9 N?
Second level.
No. 1. At what distance from the surface of the Earth is the force of attraction of the spacecraft to the Earth 100 times less than on its surface?
No. 2. Determine the acceleration of free fall at a height equal to the radius of the Earth.
Third level.
No. 1. The mass of the orange planet is 5 times the mass of the Earth. What is the radius of this planet if the free fall acceleration on its surface is the same as on Earth?
No. 2. A body weighing 1 kg is attracted to the moon with a force of 1.7 N. Assuming that the average density of the moon is 3.510 3 kg / m 3, determine the radius of the moon.
Independent work on the topic
"The movement of artificial satellites".
First level.
No. 1. Calculate the orbital speed of the satellite at an altitude of 300 km above the Earth's surface.
No. 2. Calculate the first escape velocity for Venus. Consider the radius of Venus equal to 6000 km, and the acceleration of free fall 8.4 m/s 2 .
Second level.
No. 1. The moon moves around the Earth in a circular orbit at a speed of 1 km / s, while the radius of its orbit is 384,000 km. What is the mass of the earth?
No. 2. Can a satellite revolve around the Earth in a circular orbit at a speed of 1 km / s? Under what condition is this possible?
Third level.
No. 1. The spacecraft went into a circular orbit with a radius of 10,000,000 km around the star he discovered. What is the mass of the star if the period of revolution of the ship is 628000 s?
No. 2. An artificial satellite revolves in a circular orbit around the Earth at a speed of 6 km / s. After the maneuver, it moves around the Earth in another circular orbit at a speed of 5 km/s. How many times have the radius of the orbit and the period of revolution changed as a result of the maneuver?
Independent work on the topic
"The Law of Conservation of Momentum".
First level.
No. 1. The movement of a material point is described by the equation: x=20+2t-t 2 . Its mass is 4 kg, find the impulse after 1 s and 4 s after the start of the time countdown.
No. 2. A car weighing 30 tons. Moving horizontally at a speed of 1.5 m / s, it automatically couples on the move with a stationary car weighing 20 tons. At what speed does the hitch move?
Second level.
No. 1. An icebreaker with a mass of 5000 tons. Moving with the engine turned off at a speed of 10 m / s, it collides with a stationary ice floe and moves it ahead of itself. The speed of the icebreaker at the same time decreased to 2 m/s. Determine the mass of the ice.
No. 2. A grenade flying in a horizontal direction at a speed of 10 m / s. Exploded into two fragments weighing 1 kg and 1.5 kg. The speed of the larger fragment remained horizontal after the explosion and increased to 25 m/s. Determine the magnitude and direction of the velocity of the smaller fragment.
Third level.
No. 1. A rope is selected from the boat, fed to the longboat. The distance between them is 55 m. Determine the paths traveled by the boat and longboat before they meet. The mass of the boat is 300 kg, the mass of the launch is 1200 kg. Ignore water resistance.
No. 2. Can it be argued. What is the momentum of a body relative? Justify the answer.
Independent work on the topic
"Propagation of Waves".
Option 1.
No. 1 The period of oscillation of water particles is 2 s. And the distance between adjacent wave crests is 6 m. Determine the propagation speed of these waves.
No. 2. At what distance from a sheer cliff is a person. If I clap my hands, after 1 second he heard the echo of the clap?
Second level.
No. 1. Why can transverse and longitudinal waves propagate in solids?
No. 2. 6 crests of waves passed by a stationary observer in 20 s, starting from the first one. What is the wavelength and period of oscillation if the wave speed is 2 m/s?
Third level.
No. 1. Why are the bass strings of guitars braided with wire?
No. 2. An explosion was made in the ocean at a shallow depth. The hydroacoustics of the ship, located at a distance of 2.25 km from the explosion site, recorded two sound signals, the second one 1 s after the first. What is the depth of the ocean in this area?
Option 2.
First level.
#1 What is the wavelength of a 200 Hz sound wave in air?
No. 2. A thunderclap sounded 15 seconds after the lightning flash. At what distance from the observer did the lightning discharge occur?
Second level.
№ 1. What is the relationship between the wavelength, the speed of wave propagation, the frequency of oscillations?
No. 2. The sound of an explosion produced in the water near the surface, the instruments installed on the ship and receiving sound in the water, were registered 45 s earlier than it came through the air. At what distance from the ship did the explosion occur?
Third level.
№ 2. When the boat moves in the direction of wave propagation, the waves hit the hull with a frequency of 1 Hz, and when moving towards the waves - with a frequency of 3 Hz. With what speed does the boat move relative to the shore if the water particles oscillate with a frequency of 1 Hz, and the distance between the wave crests is 5 m?
Independent work on the topic
"A magnetic field. Vector of magnetic induction.
First level.
No. 1. A straight conductor with a current perpendicular to its magnetic lines is placed in a magnetic field. How will the modulus of the magnetic induction vector change with an increase in current strength by 2 times? With a decrease in the length of the conductor by 1.5 times?
№ 2. What can be judged by the pattern of magnetic field lines?
Second level.
No. 1. What is the induction of the magnetic field in, in which a force of 0.05 N acts on a conductor with a current of 25 A? The length of the active part of the conductor is 5 cm. The direction of the induction and current lines are mutually perpendicular.
No. 2. A magnetic field with an induction of 10 mT acts on a conductor in which the current strength is 50 A, with a force of mN. Find the length of the conductor if the field induction lines and the current are mutually perpendicular.
Third level.
No. 1. Current flows in two parallel conductors. The direction of which is indicated by arrows. How do conductors interact? Prove the correct answer.
No. 2. Between the poles of an electromagnet in a horizontal magnetic field there is a straight conductor located horizontally and perpendicular to the magnetic field. What current must flow through the conductor to destroy the tension in the flexible wires supporting it? The magnetic field induction is equal to 0.01 T, the mass per unit length of the conductor=0.01 kg/m.
Solve the problem graphically.
When completing tasks 2–5, 8, 11–14, 17–18 and 20–21, write down one number in the answer field, which corresponds to the number of the correct answer. The answer to tasks 1, 6, 9, 15, 19 is a sequence of numbers. Write down this sequence of numbers. Answers to tasks 7, 10 and 16 write down as a number, taking into account the units indicated in the answer.
1
The load is lifted using a movable block with a radius R. Establish a correspondence between physical quantities and the formulas by which they are determined. For each concept in the first column, select the appropriate example from the second column.
2
A ball rolls down an inclined plane with uniform acceleration from rest. The initial position of the ball and its position every second after the start of movement are shown in the figure.
What distance will the ball cover in the fourth second from the start of the movement?
3
Three solid metal balls of the same volume, lead, steel and aluminum, fall from the same height with no initial velocity. Which ball will have the maximum kinetic energy at the moment it hits the ground? Consider air resistance to be negligible.
1) lead
2) aluminum
3) steel
4) the values of the kinetic energy of the balls are the same
4
The figure shows the dependence of the amplitude of the steady harmonic oscillations of a material point on the frequency of the driving force. At what frequency does the resonance occur?
5
Water is poured into two glass cylindrical vessels to the same level.
Compare the pressures (p 1 and p 2) and the pressure forces (F 1 and F 2) of water at the bottom of the vessel.
1) p 1 \u003d p 2; F 1 = F 2
2) p1< p 2 ; F 1 = F 2
3) p 1 = p 2; F1 > F2
4) p 1 > p 2; F1 > F2
6
A tied inflated rubber ball was placed under the bell of the air pump. Then, under the bell, they began to additionally pump air. How do the volume of the balloon and the density of the air in it change during the pumping of air?
For each value, determine the appropriate nature of the change:
1) increases
2) decreases
3) does not change
Write down the selected numbers for each physical quantity. Numbers in the answer may be repeated.
7
1 m 3 of water was slowly pumped out of the well with a pump. The work done in this case is 60 kJ. What is the depth of the well?
Answer: ______ m
8
Hot water is being poured into a thin glass beaker. Which of the available spoons (aluminum or wooden) is recommended to be lowered into the glass before pouring water so that the glass does not crack?
1) aluminum, since the density of aluminum is greater
2) wooden, since the density of the tree is less
3) aluminum, since the thermal conductivity of aluminum is greater
4) wooden, since the thermal conductivity of wood is less
9
The figure shows graphs of the time dependence of the temperature of two different substances that release the same amount of heat per unit time. Substances have the same mass and are initially in a liquid state.
From the statements below, choose two correct ones and write down their numbers.
1) The crystallization temperature of substance 1 is lower than that of substance 2.
2) Substance 2 completely passes into the solid state when the crystallization of substance 1 begins.
3) The specific heat of crystallization of substance 1 is less than that of substance 2.
4) The specific heat capacity of substance 1 in the liquid state is greater than that of substance 2
5) During the time interval 0-t 1, both substances were in a solid state.
10
Mixed two portions of water: 1.6 liters at a temperature of t 1 = 25 ° C and 0.4 liters at t 2 = 100 ° C. Determine the temperature of the resulting mixture. Neglect heat exchange with the environment.
Answer: _____ °C
11
Which of the following substances is a conductor of electric current?
1) sugar solution
3) sulfuric acid solution
4) distilled water
12
The figure shows a diagram of connecting three identical lamps to a DC voltage network.
Lamp(s) will be lit at maximum intensity
13
A magnet is inserted into a coil connected to a galvanometer. The magnitude of the inductive current depends
A. from whether a magnet is brought into the coil or taken out of it
B. on which pole the magnet is inserted into the coil
The correct answer is
1) only A
2) only B
4) neither A nor B
14
Rays a and b from the source S are incident on the lens. After refraction in the lens, the rays
1) will go parallel to the main optical axis
2) intersect at point 1
3) intersect at point 2
4) intersect at point 3
15
The nickel-plated coil of the hot plate was replaced with a nichrome coil of the same length and cross-sectional area. Establish a correspondence between physical quantities and their possible changes when the tile is connected to the electrical network.
PHYSICAL QUANTITY
A) electrical resistance of the coil
B) the strength of the electric current in the spiral
B) electric current power consumed by the tiles
NATURE OF THE CHANGE
1) increased
2) decreased
3) has not changed
| BUT | B | AT |
16
Two resistors connected in series are connected to the battery. The resistance of the first resistor is 4 times the resistance of the second resistor: R 1 = 4R 2. Find the ratio of the amount of heat released on the first resistor to the amount of heat released on the second resistor in the same period of time.
Answer: _____
17
What chemical element is formed during a nuclear reaction
18
Record the measurement of atmospheric pressure with an aneroid barometer. The measurement error is taken equal to the scale division.
1) (107 ± 1) kPa
2) (100.7 ± 0.1) kPa
3) (750 ± 5) kPa
4) (755 ± 1) kPa
19
Using a glass of hot water, a thermometer and a clock, the teacher in the lesson conducted experiments to study the temperature of cooling water over time. The table presents the results of the research.
From the proposed list, select two statements that correspond to the experiments. List their numbers.
1) The change in the temperature of the cooling water is directly proportional to the observation time.
2) The rate of cooling of water decreases as the water cools.
3) As the water cools, the rate of evaporation decreases.
4) Water cooling was observed for 46 minutes.
5) In the first 5 minutes, the water cooled down to a greater extent than in the next 5 minutes.
Read the text and complete tasks 20–22.
Superfluidity
Superfluidity of liquid helium is another unusual quantum mechanical phenomenon that occurs at temperatures close to absolute zero. If you cool gaseous helium, then at a temperature of -269 ° C, it will liquefy. If this liquid helium continues to be cooled, then at a temperature of -271 ° C, its properties will suddenly change. In this case, macroscopic phenomena occur that do not fit into the framework of conventional ideas. For example, a vessel partially filled with this strange modification of liquid helium (called helium II) and left uncovered will soon empty itself. This is explained by the fact that liquid helium rises along the inner wall of the vessel (regardless of its height) and overflows over the edge outward. For the same reason, the opposite phenomenon can also occur (see Fig.). If an empty glass is partially immersed in liquid helium, it will quickly fill the glass to the liquid level outside. Another strange property of pure liquid helium II is that it does not transfer forces to other bodies. Could a fish swim in liquid helium II? Of course not, because she would freeze. But even an imaginary ice-free fish would not be able to swim, because it would have nothing to push off from. She would have to rely on Newton's first law.
Formulating these amazing properties of liquid helium II in the language of mathematics, physicists say that its viscosity is zero. It remains a mystery why the viscosity is zero. Like superconductivity, the amazing properties of liquid helium are now under intense investigation. Significant progress has been made towards a theoretical explanation of the superfluidity of liquid helium II.
20
At what temperature does helium go into a superfluid state?
4) is fluid at any temperature
