Why does the rubber band heat up when it is pulled, from the perspective of force.

To understand this, one must look at it at the micro level. The first thing to do is to understand the structure of matter. For example, metals, for example, are microscopically composed of lattice of metal cations arranged and free electrons around the cations.

Why is such a structure stable? It is because the electrostatic repulsion between the cations maintains the distance between the cations and prevents the structure from collapsing; The electrons surround the cation to form a diffuse electron sea, which pulls the cation and prevents the structure from collapsing. Therefore, the main force that sustains this structure is the Coulomb force, which is the electromagnetic force in terms of the four basic forces.

Of course, gravitational force exists, but it is insignificant compared to electromagnetic force.

The mechanism by which elasticity is generated. Why does the metal undergo elastic deformation when extruded, resulting in elastic force? It is because under the external pressure, the above-mentioned metal structure is compressed, and the distance between metal cations in the direction of pressure decreases, which breaks the balance of the original Coulomb gravitational repulsion, and the repulsion between cations becomes larger, so the macroscopic trend shows a tendency to resist external pressure and return to its original shape, which is elastic force.

So in essence, the elastic force of the metal is the coulombic repulsion between the cations on the microscopic level, that is, the electromagnetic force in the four basic functions.

As for friction, the mechanism of occurrence is slightly different. When two metals come into contact with each other, some cations of one metal on the interface will come into contact with the electron sea of the other metal, so that Coulomb gravity occurs, as if they were one metal in this region (they didn't really fuse into one metal because the surface of the metal is uneven on the microscopic level, like a badly matched sawtooth, only a few areas are in contact with each other), so that if there is a shear force in the direction parallel to the interface, these mutually contacting regions will be misaligned, The overlapping area of the electron sea and the metal cation decreases, as if the negative charge is removed from the positive charge, so there is a reverse stress, which is the static friction. Dynamic friction is the elastic force caused by the deformation of the protruding part of the metal surface caused by the relative motion on the interface, so it is also an electromagnetic force.

As for other substances, the internal structure is different, not necessarily a simple interaction between cations and electrons, but broadly speaking, it must be the action of chemical bonds, and elastic force and friction are caused by twisting chemical bonds. And what is the essence of chemical bonds? It is the positive nucleus of the electronegative electron cloud surrounding the two bonded atoms, that is, the essence is the electromagnetic force.

When the rubber band is pulled, the external force does work on the rubber band, the energy of the rubber band increases, and the molecular movement speed accelerates, so that the rubber band will heat up. It is the internal energy that is converted into a rubber band.

You apply force to a rubber band, and the force does work on the object, and the heat generated by doing the work.

The main component of rubber bands is rubber, natural rubber is a long chain structure of polyisoprene (Figure 1), synthetic rubber is also a linear polymer with a similar structure, and the elasticity of rubber is the result of the performance of these chain link structures in different degrees of tension and contraction.

Entropy is a physical quantity used to measure the degree of molecular chaos, and when the degree of molecular chaos increases, the change in entropy output s is a positive number. When the rubber band changes between the stretched and contracted states, the entropy also changes: the structure is more ordered in the stretched state - the entropy value becomes smaller, and when it is contracted, it returns to a more chaotic state - the entropy value becomes higher (as shown in Figure 2), so the change in entropy (s) is a negative number when stretched.

When there is a change from one state to another, the energy exchange with the environment also occurs, and when the energy is transferred to the environment in the form of heat energy in a certain process under a certain pressure, the enthalpy change is negative. When the rubber band is stretched and touches the forehead very quickly, you will feel a noticeable heat, and when the tensed rubber band is held in the air for a few seconds, it will suddenly contract and quickly touch the forehead, and there will be a noticeable coolness. This is because the stronger intermolecular attraction makes the molecular arrangement more neat and orderly in the tensile state of the rubber band, and the process of forming this attraction is exothermic, so when the rubber band is tightened, there is heat transfer to the surrounding environment, that is, the enthalpy change (h) is negative when stretched.

For a spontaneous process at a certain temperature and pressure, the change in Gibbs free energy g = h t s ( g is the Gibbs free energy; t is the thermodynamic temperature or absolute temperature; h is the enthalpy change; s is the entropy change) must be a negative number because the temperature is always positive, and a negative enthalpy change and a positive entropy change (i.e., by releasing energy to the environment and entropy becomes larger) can support the spontaneous process. Of course, both factors do not have to be beneficial to the spontaneous process at the same time, and one of them can provide sufficient support at the right temperature. When the rubber band is stretched, it needs external force to provide energy, which is a non-spontaneous process (g 0), in which the entropy change and enthalpy change are negative. The contraction of the rubber band is a spontaneous process (g 0) in which both the entropy and enthalpy changes are positive.

Le Chatre's principle is the principle of balanced movement, which is an effective tool to balance the direction of movement. When an external force acts on the rubber band to make it "tight" and the balance tends to be tight, the balance will cause it to contract to slow down the degree of tension, that is, it is more and more difficult to stretch; At the same time, since the rubber band is exothermic (the enthalpy change decreases) during stretching, it will promote its contraction when it heats up. During the activity, an object of about 150 g that was stretched by a rubber band was gently placed on an electronic balance with a mass of about 20 g, and when the rubber band was heated by a high-illumination incandescent lamp, the mass was significantly reduced after about 40 seconds to 50 seconds, indicating that the tensed rubber band contracted when heated.

The simplest explanation is that friction occurs between molecules during stretching.

When he pulls, in fact, the person gives him a certain amount of energy. This energy can only be dissipated by means of heat. This is an experiment with a very obvious law of conservation of energy.

Because when you stretch the band, the molecules inside it will deform, cause friction, and eventually become hot.

Mechanical energy is converted into internal energy. When a person pulls a rubber band, he is doing work on him, and most of this energy is lost in the form of heat.

This is actually a classic thermodynamics classroom experiment that teachers usually use to help students understand concepts such as entropy, enthalpy, Gibbs free energy, etc. However, I estimate that there may be far fewer people who have heard of both than those who have heard of entropy, and it is more complicated to introduce so many new concepts, so the following is just a rough analogy to help you understand.

One (I think) easier way to understand this is to use the relatively familiar equation of state of an ideal gas. It can be assumed that elastomers and gases such as rubber bands have similar properties in this regard. Stretching rubber bands and compressed gas, the thermodynamic laws of these two processes can be compared.

The high elasticity of rubber belongs to entropy elasticity. There are a lot of long chains of polymer molecules in the rubber band, and there are some cross-links between them. In the relaxed state, the molecular chains have more room to "move freely" and can twist out a variety of different conformations.

When stretched by an external force, these molecular chains are more neatly arranged, the room for "free movement" decreases, and the entropy of this process is reduced. When the external force is removed, what causes the rubber band to rebound is the increase in entropy. The elasticity of the gas is actually entropic elasticity, but the process of reducing the entropy of the gas is compression rather than stretching.

Think of the process of rapidly stretching a rubber band as adiabatic compressing a mass of gas, both of which use external forces to reduce the entropy of the system while the temperature rises. (It's too late to exchange heat when pulling quickly, so it's considered to be an adiabatic process).

The same is true when heated. The contraction of the rubber band in the tensile state can be regarded as a change in the direction of order and disorder, and the entropy of the system increases, which can be compared to the process of expansion of gas by heat. If the tensile length is kept constant, a stronger tensile force is required to resist rebound after heating, similar to the higher pressure of a gas with higher temperatures under isochoric conditions.

Pull the rubber band hard and the rubber band will become longer because the rubber band is elastic. If you pull to a certain extent, it will become very difficult, so he will still have a certain limit, but when you let go, it will return to its original form.

The rubber band will become longer due to the tension on both sides.

Pull the rubber band hard, the rubber band will gradually become longer and longer, and the rubber band will become very elastic, and slowly pull the rubber band will break.

The rubber band will be stretched, the thickness will be thinned, and the length will be multiplied, and it will really help you look forward to adoption

It will become thinner, always in a high-intensity tensile force, and may break after a long time.

Using the properties of rubber bands that shrink when heated, a small device can also be made: rubber band heat engine. Symmetrically fasten the "spokes" made of rubber bands on a ring frame, with a hinge in the middle.

Then the side of the wheel is heated, and the heated position "spokes" shrink, so that the center of gravity of the entire "wheel" is offset, so that the wheel will move.

The tension of the rubber band will increase if you pull it hard, and if you continue to pull it, he will definitely break, and the bounce force of the break will make your hands hurt.

The rubber band was tightened a little tighter, and when I plucked it again, the sound of the rubber band became a little louder.

Pull the rubber band hard, and the rubber band will elongate and have a change in shape.

The rubber band will grow long due to the force until it can no longer withstand the tension and eventually break.

Pull the rubber band hard, and the only change in the rubber band is that it becomes longer.

Pull the rubber band hard, and the rubber band will break, and that's all.

You pull the rubber band, and the rubber band gets thinner and thinner.

Analysis: There are two effects of force: (1) force can change the shape of an object (2) force can change the state of motion of an object, including a change in the speed of motion of the object and a change in the direction of motion Answer:

Solution: When the rubber band is pulled by hand, the rubber band is elongated, indicating that the shape of the rubber band has changed, indicating that the tensile force has deformed it;

1. The rubber band will become longer.

2. The fluctuation of the rubber band will change the vibration frequency when the rubber band is elongated.

3. The rubber band converts potential energy into kinetic energy when it lets go.

If you pull hard, the rubber band will become longer.

Needless to say, it is also known that it is elongated because of elasticity.

The skin becomes longer and thinner, and it becomes more elastic.

Pull the rubber band hard, and the rubber band will definitely become longer and thinner. What else could change?

Pull the rubber band hard, and it will get longer and thinner.

First of all, your question, 1. The rubber band does the work of the opponent, just like the push and friction force when pushing the object, one does positive work and the other does negative work.

2. What is the internal energy, which is the macroscopic performance of the kinetic energy of the molecule, that is, the performance of temperature. When the elastic potential energy of the rubber band is released, it is converted into internal energy.

It has already been said. I also said ...

When the rubber band is pulled by hand, the stable molecular structure of the rubber band is destroyed, and the molecular spacing becomes larger due to deformation, which is the increase of the potential energy between the molecules, and the macroscopic performance is the increase of the elastic potential energy. After the hand is released, because the molecules tend to stabilize the structure, the molecular spacing becomes smaller, the molecular force does positive work, the molecular kinetic energy becomes larger, the internal energy increases, and the temperature becomes higher. That's about it.