What is static friction, let s talk about the concept, and give a few more examples of static fricti

The two objects have a tendency to move relative to each other, but there is no friction when they are in relative motion.

Conditions for the generation of static friction:

The contact surface is rough;

Two objects are in contact with each other and have forces acting on each other;

There is a tendency for objects to move relative to each other;

The two objects are relatively stationary.

Direction of static friction:

Determination of the direction of the relative motion trend: Assuming that the contact surface is smooth and there is no friction, the relative motion direction of the object is looked at, and the direction of the relative motion trend is determined.

Example: Applying a push force to a box on the ground, but the box does not move; Hold the glass in your hand so that it doesn't fall off.

Static friction: the friction between people walking, pushing boxes, shoes and the ground, the friction between hands and pens when writing, and the friction between hands and bottles when holding bottles;

Sliding friction: skating, ball sliding on the ground, spring dynamometer pulling block, friction between the ball and the bearing in the bearing, friction between the car sliding and the ground.

The difference between static friction and dynamic friction is:

1. The concept is different.

When an object has a relative tendency to move on the surface of another object, the force that hinders the relative tendency of the object is called static friction.

The phenomenon that hinders the relative motion of two objects that are in contact with each other is called "kinetic friction".

2. The force object is different.

Static friction is only a moving object, which is at rest; Whereas, the object of dynamic friction is different from the moving object.

3. The production conditions are different.

The conditions for static friction to arise are: the contact surface is rough; Two objects are in contact with each other and have forces acting on each other; There is a tendency for objects to move relative to each other; The two objects are relatively stationary.

The conditions for dynamic friction are: two objects are in contact with each other; Objects move relative to each other.

4. The direction of friction is different.

The direction of static friction is always along the contact surface, but when the contact surface is curved, it is tangent to the contact surface and opposite to the direction of the object's relative motion trend.

The direction of kinetic friction is opposite to the relative sliding direction of the block.

5. The determinants of friction are different.

The magnitude of the static friction force is not a fixed value, and the static friction force varies with the actual situation, and the magnitude is between zero and the maximum static friction fm. Its value can be determined by the state of motion of the object. The maximum static friction is proportional to the pressure of the contact surface, and the maximum static friction increases with the increase of pressure and decreases with the decrease of pressure.

The magnitude of the kinetic friction force is directly proportional to the positive pressure between the two objects. If the object is already moving when the thrust is 10n (whether it is acceleration, deceleration or constant velocity), then as long as it moves, then its friction force is a certain f= n So, how much force you push the effect is the same.

1. The reasons for the two are different.

Static friction is due to the tendency of one object to move relative to the surface of another non-smooth object. For example, if you hold a shovel in your hand and keep the shovel in a vertical direction, and the shovel does not fall to the ground, it is the result of static friction between the shovel and the palm of your hand. At this time, the gravitational force experienced by the shovel and the static friction force experienced by it are a pair of balancing forces.

Sliding friction is due to the relative sliding of one object on the surface of another non-smooth object. For example, in the example above, if the grip of the hand decreases to a certain level, the shovel handle will slide down the palm of the hand, and a sliding friction will be created between the shovel handle and the palm of the hand.

2. The factors affecting the size of the two are not exactly the same.

The magnitude of the sliding friction between two objects is only related to the pressure and kinetic friction factor between the surfaces of the two objects, and has nothing to do with the magnitude of other external forces. For example, if a wooden block is pulled with a horizontal force on a horizontal tabletop, no matter how large the pulling force is, as long as the wooden block is sliding, the sliding friction between the wooden block and the horizontal tabletop is constant.

When there is no relative motion between the object and the contact surface, the friction that exists is called static friction, such as an object stationary on an inclined plane, a car parked on a ramp, etc.; Or if an object is pushed forcefully without pushing, the friction between the object and the contact surface is static friction.

Static friction usually has a maximum value, and when the thrust does not exceed this maximum, the frictional force balances with the thrust.

It's like pushing a table with a force of 1n, it doesn't move, the friction force is 1n, and the friction force of 2n pushes it, and it doesn't move, and the friction force is 2n

Sliding friction is the friction that occurs when an object has a relative motion with a contact surface, such as ice skating, playing on a slide, wiping a blackboard, etc. It is only related to the roughness of the contact surface and the amount of pressure. If these two conditions are constant, the frictional force is usually constant.

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Maximum static friction = maximum static friction coefficient of the most clump bend pressure on the friction surface.

The influencing factors are divided into two:

1. It is related to the material and surface condition of the contact object, such as roughness, temperature, humidity, etc., and has nothing to do with the size of the contact surface. Under certain conditions, the dynamic friction factor can be replaced by the static friction factor generation.

2. The magnitude of the maximum static friction is proportional to the positive pressure between the two objects, that is, the normal binding force, i.e., fmax=f*fn. where f is the proportional constant, which is called the static friction factor, which is the quantity of dimension one. It is also an approximate theoretical value commonly used in engineering.