Tasks: 1. After processing on the grinding wheel, the chisel becomes hot. The chisel taken out of the forge is also hot. Is the reason for the increase in temperature of the chisels the same? 2. When the match head rubs against the box, the match ignites. Explain the phenomenon. 3. The match lights up when it is rubbed against the box. It also flares up when you bring it into the flame of a candle. What are the similarities and differences in the reasons that led to the ignition of the match in both cases. 4. Give examples of change internal energy bodies in the process of performing work under: friction, impact, compression. 5. Why does the saw heat up when you cut with it? long time? 6. Why can you burn your hands if you quickly slide down a pole or rope?
7. Why do skates glide easily on ice, but it is impossible to skate on glass, whose surface is smoother? 8. Why, when driving a nail, does its head heat up weakly, but when the nail is already driven in, a few blows are enough to heat up the head strongly? 9. What is the reason for the strong heating and combustion of artificial Earth satellites when they enter the lower dense layers of the atmosphere?
676. Is rotation a thermal motion? artificial satellite around the Earth?
No is not. Thermal motion is the random movement of the molecules and atoms that make up a body.
677. Can the movement of gas molecules be called thermal movement?
Thermal motion is a process of chaotic movement of particles. Gas molecules move chaotically, so their movement can be called thermal. 678. Can we say that the phenomenon of diffusion is caused by thermal motion?
Thermal motion is the process of chaotic movement of particles in a substance. Diffusion is the process of mutual penetration of atoms and molecules of one substance into another. The process of mutual penetration is caused by the chaotic movement of atoms and molecules, therefore, the phenomenon of diffusion is caused by thermal movement.
679. What happens to thermal motion as the temperature increases?
As the temperature increases, the speed of movement of molecules increases.
680. Will the kinetic and potential energies of water molecules in a tightly sealed jar of cold water change if it is immersed in hot water?
The temperature in the jar will increase due to the phenomenon of heat exchange, thereby increasing the kinetic energy. The potential energy will remain unchanged, since it depends on the distance between the molecules, and it does not change.
681. A freely falling ball, hitting the asphalt, jumps again, but never rises to the initial height from which it fell. Why?
Because the kinetic energy of the ball is spent on overcoming air resistance and gravitational forces.
682. A coin is tossed up. What energy transformations occur when a coin is raised? when she falls? at the moment of impact on the asphalt?
As the height of the coin's rise increases, its potential energy increases, and its kinetic energy decreases. At the highest point, potential energy is maximum and kinetic energy is minimum. As the fall begins, kinetic energy increases and potential energy decreases. At the moment before impact, kinetic energy is maximum and potential energy is minimum. Upon impact, part of the energy is converted into heat, as well as into deformation energy.
683. Why does a coin heat up when it hits the asphalt?
Because part of the coin’s energy turns into heat.
684. Hot water is poured into one glass, and cold water the same mass. In which glass does the water have more internal energy?
In a glass of hot water, molecules move faster than in cold water. Therefore, hot water has more internal energy.
685. Give examples of changes in the internal energy of bodies during their compression.
Heating the air in the pump piston.
686. How does the internal energy of bodies change during friction? Give examples.
Increasing. Sharpening a knife on a whetstone; friction of car tires when braking.
687. Does the internal energy of bodies change upon impact? Give examples.
Upon impact, the internal energy of bodies increases. Hammer operation; rebound of the ball from the floor.
688. Why does the internal energy of a spring change when it is compressed?
When a spring is compressed, its potential energy increases. Consequently, internal energy increases.
689. Does the internal energy of a gas change when it expands?
When expanding, a gas produces work against external forces, and its internal energy decreases.
690. What happens to the internal energy of liquid and solid bodies when they are heated?
There is an increase in internal energy due to an increase in the speed of particle movement.
691. Does the internal energy of ice change when it melts?
When ice melts, internal energy increases due to the supply of heat by radiation and heat transfer.
692. The friction force does work on the body. What signs indicate a change in the internal energy of the body?
When friction work is performed, the body heats up, the kinetic energy increases and causes an increase in internal energy.
How to change mechanical energy bodies? Yes, very simple. Change its location or speed it up. For example, kick a ball or lift it higher off the ground.
In the first case, we will change its kinetic energy, in the second, potential energy. What about internal energy? How to change the internal energy of the body? First, let's figure out what it is. Internal energy is the kinetic and potential energy of all the particles that make up the body. In particular, kinetic energy particles is the energy of their movement. And the speed of their movement, as is known, depends on temperature. That is, the logical conclusion is that by increasing body temperature, we will increase its internal energy. The easiest way to increase body temperature is through heat exchange. When bodies with different temperatures come into contact, the colder body heats up at the expense of the warmer one. In this case, the warmer body cools down.
A simple everyday example: a cold spoon in a cup of hot tea heats up very quickly, but the tea cools down a little. Increasing body temperature is possible in other ways. What do we all do when our face or hands get cold outside? We three them. When objects rub, they heat up. Also, objects heat up when subjected to impacts, pressure, that is, in other words, when interacting. Everyone knows how fire was made in ancient times - either by rubbing pieces of wood against each other, or by hitting flint on another stone. Also in our time, silicon lighters use friction of a metal rod against flint.
So far we have been talking about changing internal energy by changing kinetic energy its constituent particles. What about potential energy these same particles? As is known, potential energy particles is the energy of their relative positions. Thus, to change the potential energy of the particles of the body, we need to deform the body: compress, twist, and so on, that is, change the location of the particles relative to each other. This is achieved by influencing the body. We're changing speed individual parts body, that is, we do work on it.
Examples of changes in internal energy
Thus, all cases of influencing the body in order to change its internal energy are achieved in two ways. Either by transferring heat to it, that is, heat transfer, or by changing the speed of its particles, that is, doing work on the body.
Examples of changes in internal energy- these are almost all processes occurring in the world. The internal energy of particles does not change in the case when absolutely nothing happens to the body, which, you see, is extremely rare - law of energy conservation works. Something is happening around us all the time. Even with objects with which at first glance nothing happens, in fact various changes occur that are imperceptible to us: minor changes in temperature, slight deformations, and so on. The chair bends under our weight, the temperature of the book on the shelf changes slightly with each air movement, not to mention the drafts. Well, as for living bodies, it is clear without words that something is happening inside them all the time, and the internal energy changes almost at every moment of time.
