What should friction do to a body

1. According to the kinetic energy theorem, the work done by an object to overcome friction is equal to the change of the kinetic energy of the object. This is because when you apply the kinetic energy theorem, the object of study is an object
the change of the total kinetic energy of the system is equal to the work done by a pair of sliding friction forces, that is, the internal energy generated in the process

experts provide:

2. The proceres for handling the registration certificate are as follows: 1. The employment proceres of graates are generally handled by the school to the provincial department in charge of the employment of graates, and are carried out in the form of centralized handling and by stages and batches. Before graation, if the employment unit signs the employment agreement, the school employment center will go to the provincial employment center to apply for the registration certificate, and the centralized processing time is generally from June to early July. Graates who sign the "employment agreement" within the period of employment stipulated by the state after graation should first hand over the "employment agreement" to the school employment center, and the school should regularly go to the provincial employment center to handle the "registration certificate". 2. Graates who are employed in provincial institutions should hold the personnel increase plan card of government organs and institutions at the same time of applying for the registration certificate; Graates from non-state-owned units directly under the provincial government can be directly introced to the receiving units by the provincial employment center. If personnel agency is needed, the employing units shall go through relevant proceres at the provincial, municipal and county talent exchange centers. 3. The excellent fresh graates who are transferred from colleges and universities to work in township (town) organs shall apply for the "registration certificate" with the employment notice of the provincial transferred students from the Organization Department of the provincial Party committee; Graates who have been admitted as civil servants shall apply for the "registration certificate" with the certificate of the receiving unit and the employment proceres of the state civil servants. 4. After receiving the "registration card", the graates can apply to the employing unit only when they get the residence migration card from the school security office. 5. Graates who have not signed the employment agreement at the time of graation can directly apply for the registration certificate back to the place of origin for self employment according to their personal application; They can also continue to choose jobs within the period of employment stipulated by the state, and their registered permanent residence and personal files can be temporarily stored in the school for two years. However, before the graates leave the school, they should sign the "agreement on keeping the registered permanent residence and archives" with the school, so that the school can continue to provide employment services for the graates. If the employment unit has not been established at the end of the employment period, the school will directly transfer the graates' files and registered permanent residence to the talent exchange center of the personnel department of the county (city) level government where the students come from. If the employer is contacted, the local personnel department shall handle the employment proceres in accordance with relevant regulations. Graates should take the initiative to contact with the employment center of the university after the employment period, so as to provide employment services

3. Multiply by the distance
because friction does work, as long as the object is moving, it does negative or positive work.
and the distance can represent the work done all the time. Displacement is only related to the initial and final position, and has nothing to do with time
of course, if it is moving in a straight line, it is better understood. Multiply by the distance

4. The calculation method of friction force is different between sliding friction force and static friction force. When calculating the friction force, we must distinguish between static friction force and sliding friction force= μ FN calculation. (1) according to the force on the object, calculate the positive pressure on the object FN. (2) according to the formula F= μ 2. Two force balance method: the object is in a state of equilibrium (uniform velocity, static positive), and it is solved according to the two force balance condition. 2. Calculation of static friction. 1. Balance condition method is used to solve the static friction. As shown in figure 3-3-19, a static object is placed on the horizontal plane. When a person pushes the object with horizontal thrust, the object is still, According to the balance condition of the two forces, the static friction is equal to the thrust. 2. The static friction is a passive force, which changes with the change of the external force; F ≤ Fmax is independent of the positive pressure between objects, so the formula F cannot be used= μ 3. Maximum static friction Fmax The value is equal to the external force along the contact surface when the object is just sliding, which is the maximum value of static friction and greater than sliding friction. Generally speaking, they are equal, and the maximum static friction is Fmax.. The formula is Fmax= μ Static FN, μ Static is the static friction coefficient and specific dynamic friction coefficient between objects μ As shown in figure 3-3-20, the dynamic friction coefficient between the object and the ground is 0.5, and the maximum static friction and sliding friction are regarded as equal, giving the object a horizontal thrust. (G is taken as 10N / kg) (L) when the thrust is 5N, how much is the friction between the ground and the object 2) When the thrust is 12n, how much is the friction force between the ground and the object? Comments: when calculating the friction force, we should first

5. The power of work done by friction requires the amount of work first. The power of work done by friction is obtained by multiplying the friction by the distance of moving in the direction of friction, and then dividing the work by time

6. The answer is B and C
when you push the car and the car doesn't move, the static friction of the car does negative work, and the static friction of the elevator (that kind of slant) in the shopping mall does positive work. B is correct '
sliding friction is relative movement, and friction is generally the force to keep the object moving. Then the original object should be relatively static and sliding friction under the action of other forces, So sliding friction can only do negative work.

7. The formula w = f * s

requires the displacement of the object under the action of force, that is, the generation of active work, When does the static friction force proce displacement?

two books are stacked on the table and only pull the books below to cause movement?
there is friction between the two books.
if the books on the upper side move together, there will be relative stillness. At this time, static friction is actually at work.
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the static friction force is consistent with the tensile force and also proces displacement. In this case, the static friction force is used to do work