Junior High School Physical Friction Limit, Junior High School Physical Friction

It's because there is static friction when it's stationary and sliding when it's sliding, and the two frictions aren't the same, and the maximum static friction is the same as sliding friction (note that static friction is not a fixed straight, but sliding friction is straight.

The magnitude of the sliding friction force is directly proportional to the pressure, that is, to the perpendicular force of one object to the surface of another object. The sliding friction force is calculated as f = fn

where f is equal to the sliding friction, which is the coefficient of dynamic friction, and fn is the pressure.

At the beginning of the push, the friction force and your thrust force balance f=5n, and the second uniform linear motion f=6n, although the pressure does not change, the friction coefficient changes, so the friction force also changes.

The first time the table did not move, but there was a tendency to move, and the table was subjected to static friction; The second time the table moved, and it was moving in a straight line at a constant speed, and it was affected by the balance force, and the sliding friction was equal to my thrust. The friction force is not equal twice. There is a maximum static force.

The action of the force is mutual, so the frictional force for the first time is only 5n.

And because it is a uniform linear motion, the second frictional force is equal to the force you push has 6n.

You're actually wondering about the question of static friction vs. sliding friction – the maximum value of static friction is greater than that of sliding friction. Static friction is the motive force, as long as it does not move, it is equal to the thrust, and the sliding friction is always a constant value.

Equilibrant. It's not the so-called what is the maximum friction.

The maximum friction is also not 6N

The maximum friction is a little more than the friction when moving at a constant speed... That's a very small point.

There is no such a boundary.

Factors influencing the magnitude of sliding friction - junior high school physics easy learning to share a set of interesting teaching courses, which is more fun, including all junior high school physics knowledge points, synchronous course explanation, and after-class exercises. Like friends like, favorite,**. Follow me and continue to share quality teaching every day**.

Equal. When your thrust is greater than the static friction, it moves.

Action and reaction forces!

1. Use force to pull the wooden block, and the wooden block moves in a straight line at a uniform speed.

It shows that the force of the wooden block is balanced at this time, and it can be seen that the friction force on the object is.

The sliding friction experienced by the object is independent of the state of motion, so no matter how much external force it is subjected to, or how much other external force it is, as long as the wooden block is moving, the sliding friction force is.

Sliding friction is related to two factors, one is the roughness of the contact surface and the other is the amount of pressure. In this problem, the roughness of the contact surface has not changed, and the pressure has not changed, so the sliding friction is always It's just that this is the linear motion of the wooden block at variable speed, because the tensile force is greater than the friction force, so it is not the equilibrium force, so the linear motion of variable speed is done. The known condition is that there is a wooden block of mass on the table, and the wooden block is pulled by force, and the wooden block moves in a uniform linear motion tells us that the friction force is, because the friction force and the tensile force cancel out (balance force), and become a balance force, and the wood block will continue to rely on inertia to advance, and it is a balance force, so it moves forward at a uniform speed.

In junior high school, sliding friction is related to two factors, one is the roughness of the contact surface, and the other is the amount of pressure. In this problem, the roughness of the contact surface does not change, nor does the amount of pressure, so the sliding friction is always there.

Note: The amount of friction is only related to the positive pressure and the roughness of the contact surface (i.e. the coefficient of friction).

When the wooden block moves in a uniform linear motion under the action of 6n force, it means that the object is balanced by force in the horizontal direction, that is, the tensile force and the sliding friction force are equal (6n).

When the external force becomes 7N, although it will cause the force to be unbalanced in the horizontal direction, the friction force is still 6N because the positive pressure and the contact surface do not change.

When the force is used to pull the wooden block, the wooden block moves in a uniform straight line, indicating that the force is balanced at this time, so the friction force is when the force used pulls the wooden block, the pressure does not change, and the roughness of the contact surface does not change, so the friction force is still at this time.

Because the original wooden block is made of uniform linear motion, it is in a state of equilibrium, and the force on it is a balanced force, vertically: the gravitational force it receives and the supporting force of the table on it are balanced with each other, and in the horizontal direction: the tensile force and the sliding friction force are balanced with each other, and the magnitude is equal, so the friction force is also the same.

Later, after the wooden block was removed from the tensile force, it continued to move, indicating that it was still subject to sliding friction, and the sliding friction was only related to the pressure and the roughness of the contact surface, and the conditions of these two conditions did not change, so the sliding friction did not change.

The bottle is moved downward by gravity, but because the bottle body remains upright and the hand holding the bottle hinders the downward movement of the bottle, the bottle is in equilibrium at this time, so the direction of friction is correct upward (it can be seen from the balance of two forces that the two equilibrium forces acting on the same object are in opposite directions). Hold the bottle in your hand, the force of holding the bottle is not friction for the bottle, what keeps the bottle balanced in the vertical direction is the friction between the hand and the bottle and the balance of the bottle's own gravity, for example, if you go to get the glass after washing your hands, you will feel that the glass is very easy to fall down, and the force of holding the bottle also has a force effect on the bottle, making the bottle body deformed. To sum up, what keeps the water bottle balanced in the vertical direction is the balance of the friction between the hand and the bottle and the gravity of the bottle itself, and this friction is correct in the vertical direction and is not outward.

Friction is the force that hinders the movement of an object or the relative movement trend, the bottle is subject to gravity, so the movement trend is vertical downward, and the bottle remains stationary, so friction and gravity are a pair of balanced forces, so the friction force and gravity are opposite to the direction of gravity, that is, the direction is vertical.

In this case, the resistance is equal to the product of the positive pressure and the coefficient of friction, and the outward is not the frictional force, but the positive pressure.

Because there is gravity, it is straight down.

Let the sliding friction experienced by a be f1=

B moves at a constant speed, A also moves at a uniform speed, so the horizontal direction is balanced by two forces, so the tensile force of the rope to A is t=f1=4n

Therefore, the upper surface of the long plank b is subjected to friction force f1'=4n, direction to the left.

b should also have a two-force balance in the horizontal direction, and the force to the left is t+f1'+f ground, the pull to the right is f

So t+f1'+f地 =f

f ground = f-t-f1'=17-4-4=9n

That is, the frictional force experienced on the lower surface is 9n

The friction force experienced above the plank b is 4 N, the direction is horizontal to the left, and the friction force on the lower surface is 13 N, (17 N-4 N) and the direction is also horizontal to the left, and the aspect of the object that is subjected to friction is opposite to the direction of the relative motion of the object.

f=2kg*10*02=4n

Rightward. f=f=17n

Left. Two forces are balanced.

f=2kg to the left b to the right to move at a constant speed Two forces balance f=17n to the right.

Ask the landlord first, have you learned Newton's second law?

If we know this law, we should know that the direction of acceleration is the same as the direction of the resultant force.

When an object moves with rightward acceleration (the object has rightward acceleration), the frictional force is the resultant force in the horizontal direction and the direction of action on the object is to the right, since the horizontal direction is only affected by the frictional force. When decelerating to the right (the object has acceleration to the left), the friction is to the left.

Analyze the force of an object from the motion of the object, or analyze the motion of an object from the force of the object.

In addition, inertia is an intrinsic property of an object, and when the resultant external force on the object is zero, the object will move in a uniform straight line or at rest (Niu 1). The workpiece and the conveyor belt move together at a uniform speed to the right, and the reason why the friction force is zero is that it is in a state where the external force is zero.

Once an object accelerates, it proves that the net force it is subjected to is not zero, and you can judge the direction of the net force on it from its motion.

1.When doing uniform linear motion, the object has no relative tendency to motion, so it is not subject to friction.

2.When accelerating, there can only be friction in the horizontal direction The conveyor belt accelerates to the right The object is on the conveyor belt, relatively stationary with the conveyor belt, and the object also accelerates to the right The object accelerates horizontally to the right, and the object is subjected to the static friction force to the horizontal to the right.

2.The conveyor belt decelerates to the right, the moving object also decelerates to the right, and the object accelerates horizontally to the left, and the object is subjected to the static friction force of the horizontal to the left.

First of all, at a constant velocity, the object moves with the conveyor belt, relatively stationary between them, so the frictional force is 0, and then accelerates to the right, by Newton's second law f=am, the direction of the resultant external force is the same as the direction of acceleration, and the direction of friction is opposite to the direction of acceleration, if it decelerates to the right, the direction of acceleration is to the left, and the direction of friction is to the right.

Because there is the presence of static friction. A stationary object can only move if the thrust it receives exceeds the maximum static friction, and the friction after movement becomes kinetic friction. Generally, the maximum static friction will be slightly greater than the dynamic friction.

The first time, the thrust has not yet reached its maximum near friction, so it is still stationary.

The second problem is the determination of the direction of friction. The direction of static friction is related to the relative motion trend of the object. Since the thrust is horizontal, the object has a tendency to move in the direction of the force relative to the ground, and the static friction at this time is the opposite of the motion trend.

The object is in equilibrium, and in the horizontal direction, the thrust and static friction are balanced. When exercising, the dynamic friction is opposite to the relative direction of motion, that is, the dynamic friction at this time is opposite to the direction of motion and is also in the horizontal direction. The object is still in equilibrium, and in the horizontal direction, the thrust and static friction are balanced.

Well, the direction of friction and gravity are perpendicular to each other, not the opposite, and very rarely, these two forces will balance yes.

In both cases you mentioned, friction is not balanced with gravity, both are balanced with thrust.