Senior 1 Physics Problems Why does friction do work

There are two factors for doing work:1Force, 2, displacement in the direction of the force. As long as these two factors are present, then the force is done.

In this question, it can be divided into two processes, ascending and descending, in the ascending process, the air resistance.

Friction) is present (as long as the object is moving, it will rub against the air) and the direction of resistance is straight down, and the direction of motion is upward, so the work in this process is -h*f=-hf

In the process of descending, the same is true of the work, which is -hf, so the total work is -2hf, if there is any question, you can ask me.

If you're satisfied, please choose the answer

Because the direction of the frictional force of the air on the ball is opposite to the direction of motion of the ball, it is all negative work.

Therefore, in the process of the ball rising, the friction force direction is downward, and the work done is w1 = -fh In the process of the ball descending, the friction force direction is upward, and the work done w2=-fh, so the friction force in the whole process does the work w1+w2=-2fh

The work done by gravity is characterized by being path-independent. But not all forces are the same as gravity.

The direction of friction is opposite to the direction of relative motion, so in the process of upward movement, the friction force does negative work downward, and in the process of downward movement, the friction force goes upward, and still does negative work.

Friction is the force of air acting on an object, and the object moves in the opposite direction of friction, so friction does negative work.

When the object goes up, the friction goes down, and when it comes down, the friction goes up

The frictional force is always in the opposite direction of velocity and does negative work all the time.

So the whole process is -2fh

The frictional force is always opposite to the direction of the relative motion of the object, when the object rises, the work done is -fh, and when it falls, the work done is also -fh, so the whole work is done: -2fh

S in the calculation of the work done by friction is not displacement, it is the distance, so w fs f2h

Because the direction of air resistance is always opposite to the direction of motion, regardless of upward or downward motion, friction does negative work.

When asking questions in the future, it's best to say exactly what you're confused about.

It seems that you are one of the students who are not willing to make the effort to grasp the basic physical laws and concepts, and if you take a test of your knowledge, you probably belong to the kind of students who don't know anything.

This question is actually very simple, and it is the most basic thing. Click to enlarge

You first understand the definition of work, the calculation formula, the principle of the relationship between work and energy, and the kinetic energy theorem. If you don't have any concept in your head, you won't be able to learn these things.

1.Use the expression of constant force to do work to find the frictional force to do work.

The frictional force on the inclined plane is equal to mgcos, which is the inclination angle of the inclined plane, and the length of the bottom edge of the inclined plane is x, then the work done by friction is mgcos x cos, that is, mgx.

Friction does work on a horizontal plane mgx', where x'is the length of the horizontal plane.

It is not difficult to see l x+x'

So the work done by friction is mgl.

2.Use the kinetic energy theorem to find the frictional force to do work.

mgh-w＝0

So the frictional force does the work as mgh.

From the above analysis, it can be seen that it is easy to solve by the kinetic energy theorem.