Asking a junior high school physics question has been very tangled, and I hope the masters will answ

A: I think the root cause of your problem is a lack of understanding of sliding friction and static friction.

One. We say that the magnitude of friction is related to the magnitude of pressure, which is based on the study of sliding friction. That is: the magnitude of the sliding friction is related to the magnitude of the pressure (specifically, the friction is proportional to the pressure when the roughness is the same);

Two. Under the premise of static friction, the static friction is independent of the magnitude of the pressure. This frictional force is only related to that force that causes the relative tendency of the object to move.

Three. In this example, the static friction is always equal to its gravitational force (both are equilibrium forces), regardless of the amount of pressure.

If you are attentive, you must understand!

1) The static friction varies between 0 and the maximum static friction, and the specific values are analyzed by the balance of two forces.

2) It is true that sliding friction is related to the roughness and pressure of the contact surface. But the first pressure in this problem is not the pressure in the sliding case, and the second pressure is the pressure in the sliding case.

3) Both the state of rest and the state of uniform linear motion are in equilibrium, and the two forces are balanced by the equilibrium force, and the static friction force and the sliding friction force are equal to gravity, and the direction is equal to gravity.

Because he is still so balanced, the resultant force is zero, of course, it does not change. Otherwise, if you have a lot of pressure, the friction is very strong, and the gravity is the same, so will the object be pressed up by you? The horizontal moving object has a frictional force greater than the pulling force, and it will slow down and move to zero, then you have a lot of pressure and a lot of friction, and once you stop, then there is no friction and it becomes zero.

The object is stationary, and the pressure and support are balanced. When the car brakes, the wheels do not rotate, it is friction and deceleration, and finally it stops, the same reason.

Because friction is divided into dynamic friction and static friction, it is true that they are all related to pressure, but the nature of the front and rear friction has changed, and the object is subjected to static friction when it is stationary, and with the increase of static friction, the maximum object moves, then it is dynamic friction, which is smaller than the maximum static friction, and the dynamic friction coefficient is also less than the static friction coefficient. ok

In the stationary state, the pressure changes the maximum static friction, and does not change the actual friction of the object, so it is 5N

The two equilibrium states of an object at rest and in a uniform linear motion will reach a two-force equilibrium in the equilibrium state. Gu will be the same as gravity.

Because of the balance of forces, you say that pressure is related to friction, and you understand that in the case of the motion of an object, I understand it, and I agree with it.

f= n refers to the sliding friction force, and the pressing is the static friction force, and the static friction force is usually analyzed from the physical force balance

is the maximum static friction. Target.

Summary. It is not right to convert electrical energy into internal energy, it is mainly converted into light energy, which is the role of lighting, and secondly, it will generate heat in the process of its conversion, which is heat energy.

Ask a junior high school physics question.

Does the light bulb convert all the electrical energy into internal energy, and then part of the internal energy into light energy?

Does the light bulb convert all the electrical energy into internal energy, and then part of the internal energy into light energy?

Most of the electrical energy of the light bulb is converted into heat.

There is also light energy, light energy is the main one, and heat energy is secondary.

It is not right to convert electrical energy into internal energy, it is mainly converted into light energy, which is the role of lighting, and secondly, it will generate heat in the process of its conversion, which is heat energy.

Then why can light bulbs use Joule's law.

It is not all converted into internal energy.

Why? The reason for kissing is that he first converts all of it into internal energy, and then continues to convert it outward into light and heat.

So he can use Joule's law.

Good. The light bulb is a pure electrical resistor that emits light by generating heat, while joules are used to calculate heat, so Joule's law is used.

Answer: The correct one is A.

a.The nature of microwaves is closer to that of light waves, and they probably propagate in a straight line (at the beginning of the second paragraph on page 108 of the second volume of the second volume of the Physics Textbook).

b.By evenly deploying 3 synchronous satellites around the earth, global communication can be realized, (false!) Because there are many satellites, not all satellites can do, and they must be communication satellites, so it is changed to "3 synchronous [communication] satellites" (the fourth line of the last paragraph of page 108 of the second volume of the physics textbook).

c.Optical fiber communication is to use ordinary light sources to transmit information in optical cables (false!). If the ordinary light source is not good, it must be a single frequency.

1. Lasers with a high degree of concentration in the direction) (the penultimate line of the first paragraph on page 109 of the second volume of the physics textbook of the People's Education Edition).

d, the most commonly used form of network communication is e-mail (false!). It's just often used.,It's not "the most commonly used".,It's not the same with one more word.,Hehe)(The beginning of the second paragraph on page 112 of the second volume of the physics textbook of the People's Education Edition)

I'm a teacher, I hope I can help you, thank you!

Well, I'm in the second year of junior high school, but we learned power in the second year of junior high school. However, I can tell you that microwaves are electromagnetic waves, and the speed of electromagnetic waves is as fast as the speed of light traveling in a vacuum, so microwaves are close to light.

c is not using an ordinary light source, it is a laser beam.

Personally, I think d, because the metal ball will float in B.

Not the same f=g=mg s= different volume, others are the same, so they are different, but the pressure on the ground is the same p liquid = f s = g s = mg s= liquid vg s= liquid shg s= liquid hg= liquid gh h is the depth.

It should be noted that the difference between pressure and pressure is that of the same liquid, one is the volume determines the size, and the other is the depth determines the size. The misunderstanding of your problem is that many people use pressure to calculate the pressure, and the pressure must be the same, but it is the liquid vg that determines the pressure

Hehe, many people say the same thing, if you don't believe me, you can ask your teacher.

The pressure at the bottom of the bottle is p=egh, that is, p (pressure) = e (density of the liquid) * g (constant = depth immersed in the liquid), from the meaning of the title: h and e are the same, g is constant, so the pressure on the bottom of the last two bottles is equal.

Equal. According to the liquid pressure formula P=PGH, the pressure at the bottom of the bottle is equal due to their equal height. And because the pressure f=ps,s is equal, the pressure on the bottom of the SO bottle is equal.

The pressure is the same.

Because f=mg=density volume g density s h g,s is the same, h is the same, density and g are also the same, so the pressure is the same.

The same f=p*s=p, water, gh*s, can be seen from this equation, independent of volume.

f. Pressure: p. Pressure: s, bottom area, p. Water, water density, g, gravitational acceleration, h. Water height.

Equal. Pressure f=ps=p, water, ghs

P water is equal, g is certain, h is equal, and s is equal.

So the pressure f is equal.

If Xiao Ming closes the switch without checking the circuit, the phenomenon that will occur is a short circuit.

The current in the two lamps is, in addition to the error in (1), there is also a deficiency or error in the range selection.

Burn out ammeter A1, A2. The range of ammeter A1 and A2 is too large, and the gear should be selected. Now the circuit is in series, not in parallel.

1. There is a short circuit and the power supply is burned.

2. The range of the A1 meter is selected incorrectly, and the application, the ammeter should not be connected in parallel with the electrical appliance, and should be replaced with a voltmeter.