How do you determine friction in some situations? Expedited .

1.Opposite to the direction of motion, at the place where the two objects come into contact.

2.It should be the active part, that is, the force point. The whole doesn't say anything, only the position where the force is applied.

3.If you don't need a force analysis diagram, you should grasp the concept, for example: the direction of friction is always opposite to the direction of motion, etc., and you should pay attention to reality and pay more attention to the details of life; If there is a picture, it is necessary not only to have a concept, but also to draw the picture accurately and make correct judgments.

The trick is not very good, do the questions appropriately, and be able to summarize the good method by yourself.

The direction of friction has to be judged according to the relative object, that is, the relative friction, and the direction of friction is different for different reference objects! That's why friction can also act as a driving force for the motion of an object!

It's actually quite simple.

Friction is the force that involves between two objects.

Taking one of the objects as a reference, to see in which direction the other object is moving relative to this object or in which direction it has a tendency to move, the direction of friction is the opposite direction of relative motion.

1 The direction of friction is opposite to the relative direction of motion, such as the rear wheel of the car is the driving wheel, and the frictional force received by the front wheel is forward, and the front wheel is the frictional force received by the driving wheel backward.

2 There are two ways to find friction Friction There are two ways to find friction: the integral method and the isolation method which vary depending on the problem.

3 Do more questions, and it's good to do more.

The magnitude of friction is related to the following three factors:

1. The roughness of the contact surfaceThe roughness of the contact surface is greater, the greater the friction between objects.

2. Cavity pressure of the contact surface: the greater the pressure of the contact surface, the greater the friction.

3. Whether it is rolling friction, static friction or sliding friction: sliding friction and static friction are more frictional than rolling friction.

When two objects in contact with each other are in relative motion or have a tendency to move relatively, a force that hinders the relative motion or tendency to move on the contact surface is called friction. The direction of friction is opposite to the direction of the relative motion of the object (or relative motion tendency). There are three types of friction: static friction, rolling friction, and sliding friction.

Factors that affect friction are: the amount of pressure, the roughness of the contact surface. Moreover, the relationship with these two quantities is "proportional."

Friction is the force of two objects that are in contact with each other and squeezed against each other, and if there is or is about to occur "relative motion" between them, there will be a kind of friction force on the contact surface that prevents this relative motion.

In its large wheel, the frictional force that causes relative motion is sliding friction, and vice versa.

Similarly, the scientific method used is the "control variables" method. That is, when studying the relationship between friction and pressure, it is necessary to ensure that the roughness of the contact surface is constant, and the conclusion is drawn by changing the pressure.

It is judged by whether there is a relative displacement between the study subjects.

Let's look at a more complex case, as shown in Figure 2. If m is at rest with respect to the ground and m is at rest with respect to m under the action of f, then both forces are static friction; If m is displaced relative to the ground under the action of f, and m is stationary relative to m, then the friction between m and the ground is dynamic friction, and the friction between m and m is static friction; If m is displaced relative to the ground under the action of f, and m is displaced relative to m, then the friction between m and the ground is dynamic friction, and the friction between m and m is also dynamic friction.

Formula for friction: f= fn (fn: positive pressure (not necessarily equal to the gravitational force of the object) Friction is the opposite force produced by the relative translation or relative translation tendency of the object on an unsmooth surface, and the magnitude of the frictional force is determined by two values.

Vertical pressure and coefficient of friction.

1. Sliding friction: f= m f

Note: Fn is the elastic force between the contact surfaces, which can be greater than g; It can also be equal to g; It can also be less than g

m is the sliding friction factor, which is only related to the material and roughness of the contact surface, and has nothing to do with the size of the contact area, the relative motion of the contact surface and the positive pressure n.

2. Static friction: its magnitude is related to other forces, which is solved by the equilibrium conditions of the object or Newton's second law, and is not proportional to the positive pressure.

Size range: o f static fm (fm is the maximum static friction and is related to the positive pressure).

Description: a. The friction force can be the same as the direction of motion, or it can be opposite to the direction of motion.

b. Friction can do positive work, negative work, or no work.

c. The direction of friction is opposite to the direction of relative motion between objects or the direction of relative motion tendency.

d. Stationary objects can be affected by sliding friction, and moving objects can be affected by static friction.

3. Rolling friction.

When an object rolls on the surface of another object, the obstruction effect on the rolling caused by the deformation of the two objects under pressure on the contact part is called rolling friction.

Rolling friction is the frictional force experienced by the object when the contact surface is constantly changing when the object is rolling. It is essentially static friction. The contact surface is soft, and the greater the shape change, the greater the rolling friction.

In general, the rolling friction between objects is much less than the sliding friction. Rolling bearings are widely used in the transportation and mechanical engineering industries to reduce friction. For example, the friction of the driving wheels of a train is the driving force that pushes the train forward.

The static friction of the driven wheels is the rolling friction that hinders the progress of the train.

To put it simply, friction is the opposite force caused by the relative translation or relative translation tendency of an object on an unsmooth surface, and the magnitude of friction is determined by two values. Vertical pressure and coefficient of friction. Pin one of the values.

The other value is linearly proportional to the frictional force. The direction is always parallel to the contact surface and prevents the relative motion from taking place.

There are rolling friction and sliding friction, but the formula is f= n