Sophomore Physics Thermal, about Sophomore Thermal, thank you

Analysis: (1) Although the rate of molecular thermal motion is large, the collision between molecules is very frequent, because the frequent collision makes the movement of molecules no longer uniform linear motion, the molecules have gone through a tortuous journey before reaching the nostrils, and a certain amount of molecules is required to cause people's sense of smell; The propagation rate of sound waves is about the same as the rate of molecular thermal motion, and the propagation distance is also equal, but sound waves travel in a straight line in the air and take a shorter time to reach the receiver, so the noise is heard for a longer time before the smell is smelled

2) Friction welding is the use of molecular gravity The two contact surfaces of the weldment rotate in opposite directions at high speed and add a lot of pressure, so that the two contact surfaces can be melted, so that the distance between most molecules reaches the range of obvious molecular force, and a large number of molecular distances reach the distance range of gravity by friction melting, so that the two weldments become a whole

The direction of the thermal motion of the molecule is indefinite, and although it is very fast, it actually makes many, many detours, like getting lost and turning around. Just as a classroom buys something delicious and puts it at the door, it will not say that the whole teacher is a taste for a moment, reflecting the disorder of molecular thermal movement.

Friction welding uses high pressure to achieve molecular forces at the distance between the two contact surfaces"Spheres of influence"Through a strong molecular attraction, the two contact surfaces become a whole.

The first problem is that the thermal motion of the molecules is chaotic and directionless, one moment in one direction, the next moment in the other direction, and generally the smell is due to the convective diffusion of the gas.

The second problem is that a large amount of heat is generated in high-speed friction, which makes the weldment molecules permeate and fuse each other with vigorous movement, and the welding is successful after the temperature is reduced.

We hope you are satisfied!!

Why the speed is the same at this time, it is completely a problem of kinematics, the conservation of momentum is the method of solving the final velocity, at the beginning the two cars are close to each other, after a period of time, the speed of car A is reduced to zero, and then it begins to accelerate to the left, B is still to the left, deceleration, at this time it is a catch-up problem, as long as the speed of car B is still greater than the speed of car A, the two are approaching, when the speed of the two is the same, the closest, and then the speed of car A begins to be greater than the speed of car B, and begins to move away from each other.

The calculation is a theorem for the conservation of momentum, which stipulates that to the left is positive m B * v B - m A * v A (m A + m B) * v ' to solve v' 4 3 (m s).

This question doesn't need to be solved, it won't be tested, this model is wrong, and the teacher is afraid of being laughed at.

First question: The Coulomb force acts as a centripetal force to find the kinetic energy of the electrons.

The second question: In fact, it is to find the period when the electron moves in a circle.

Question 3: Use i=q t to find the current.

This problem is obviously solved using the nuclear model of the atom.

The electrons move in a uniform circular motion around the nucleus, and the centripetal force is the Coulomb force experienced by the electrons.

1) Ke (squared) r (squared) mv (squared) r, so the kinetic energy of the electron e 1 2 mv (squared) = ke(squared) 2r

2) f=v 2 r= under the root number: .1 2 r(3) electrons move in a circular motion on the track, which is equivalent to a current passing through the electronic track, and the amount of charge passing through it per second is q=ef

So the current i=q t=ef t=ef= under the root number:. e/2πr（t=1s）

For option a, the following explanation is given: the repulsion between gas molecules is negligible, because the spacing between gas molecules is very large, and the situation of gas is different from liquid and solid, when the temperature increases, it is because the energy of the molecule becomes larger, and the kinetic energy increases, so the pressure increases.

Option b explains as follows: when the temperature increases, it is because the energy of the molecule increases, the kinetic energy increases, so the pressure increases.

Option C explains as follows: During the exposure to the sun before the burst, the gas absorbs heat, and because the temperature increases, its internal energy must increase, keeping in mind that the energy absorbed is greater than the energy released.

Option D is explained as follows: at the moment of sudden burst of the tire, the temperature does not change from the outside world, but the volume increases, the temperature does not change, the volume increases, and the internal energy decreases.

That's it.

I'll just say what's wrong?

aThe distance between the molecules of a gas is very large, and no repulsion is generated.

b molecular irregular motion intensifies, kinetic energy increases, the force per unit time unit area of the tire increases c gas heat absorption, molecular irregular motion increases, kinetic energy increases, potential energy is still zero, so the internal energy increases d tire burst, gas overflow, molecular weight decreases, thermal motion weakens, internal energy decreases.

Internal energy is the embodiment of the irregular motion of the molecules of an object.

Friction can be understood as the interaction force between the molecules on the lower surface of the object and the upper surface of the table, which hinders the movement of the object, and this part of the energy becomes the irregular motion of the molecules on the lower surface of the object and the upper surface of the table, that is, it becomes the internal energy of the object and the tabletop.

In addition, even if only the temperature increase in the object can be increased, the heat can be transferred to the tabletop Q: Isn't it only the friction of the desktop that does work on the object?

Answer: From a microscopic point of view, the friction of the object on the table is also doing work on the molecules on the surface of the table, causing them to vibrate more violently near the equilibrium position and increase the internal energy.

The energy is conserved, and some of the energy is transferred to the internal energy of the table.

It's friction that does it.

What is involved here is the phenomenon of heat. Hence there is also the part that is converted into the internal energy of the molecule.

When the air is heated, the rapid movement of air molecules will accelerate, which makes the volume of air increase with the increase of temperature. When the table tennis ball is placed in hot water, the air in the table tennis ball is heated, and the molecular thermal motion of the air in the table tennis ball intensifies, and the number of times the molecules hit the inner wall of the ball becomes larger per unit time, so the pressure will become larger

Assuming the piston does not move:

p0= pa, t0=300 k

p1, t1=400 k

p0/t0=p1/t1

p1=p0t1/t0= pa

Then the friction that the piston should provide = (P1-P0)S = >5N, so the piston cannot provide such a large friction, it must slide, the temperature is added slowly, so the piston is also moving slowly, and the final state friction is 5N.

The pressure p2 and volume v2 of the real Yu Xinji friend are good to dig the core

p2-p0)s=f

p2=p0+f/s= pa

p0v0/t0=p2v2/t1

v2= m^3=127 cm^3

Gas volume 127 cm3

From the title, it can be known that the internal resistance of the ammeter and the current flowing through the voltmeter can be ignored. Assuming that the electromotive force and internal resistance are u,r, when the switch is disconnected, the voltmeter measures the electromotive force of the power supply, so the electromotive force u=6 volts.

When the switch is closed, Ohm's law is applied to the whole circuit: u = u = 6, so r = 1 ohm.

The voltmeter resistance is very large, and the ammeter wire resistance is very small, then they see that the circuit has no effect.

When the switch is disconnected, the voltmeter measures the voltage of the power supply, which is equal to the electromotive force of the power supply.

The switch is closed, the voltmeter reads is, the current is, this current can also be seen as the current flowing through the power supply, the voltage divided by the current.

According to the meaning of the title, the internal resistance of the ammeter is ignored, and the internal resistance of the voltmeter is infinity.

If the electromotive force of the power supply is 6 volts, the resistance of the resistance is 4 ohms, and the voltage is divided by the current, and the internal resistance of the power supply is volts divided by amperes of 1 ohm.

It is important to note that after the circuit is closed, the voltage measured by the voltmeter is the voltage of the external circuit, not the voltage of the power supply. When the switch is turned on, the voltage of the voltmeter is the power electromotive force.

The electromotive force of the power supply is 6V, and the internal resistance value is (

In closed conditions, the pressure possessed by a vapor that is in phase equilibrium with a liquid or solid at a certain temperature is called saturation vapor pressure. The same substance has different vapor pressures at different temperatures and increases as the temperature increases. The saturated vapor pressure of different liquids is different, and the saturated vapor pressure of the solute is greater than the saturated vapor pressure of the solution. For the same substance, the saturated vapor pressure of the solid state is greater than that of the liquid state.

For example, at 30, the saturated vapor pressure of water is and ethanol is. And at 100, the saturated vapor pressure of water increases to , ethanol is. Saturation vapor pressure is an important physical property of liquids, such as the boiling point of liquids, the relative volatility of liquid mixtures, etc.

Saturated vapor pressure is a function of temperature and is independent of volume.

Wrong, saturated vapor pressure is only related to temperature.