Hold a bottle in your hand so that it remains upright and stationary, if you increase grip strength

The bottle is always balanced by force, and gravity is equal to friction. If the friction increases, doesn't the bottle fly upwards? When holding the bottle, the friction force experienced by the bottle is static friction, which has nothing to do with pressure, only sliding friction is related to pressure.

d.The role of force is the interaction of two li. Since the bottle remains upright and stationary, gravity = friction and then hold it harder.

The bottle is also stationary. So it's still equal to gravity. So the frictional force does not change.

If the bottle has a slow sliding phenomenon. then hold it harder. Friction increases.

To make the bottle not move, it must be balanced by the force, so his friction is equal to gravity, so his mass does not change, and gravity does not change, so the friction does not change.

Because gravity has not changed, the friction force must not change, that is, d, it has nothing to do with the grip force, they do not affect, and the balance of 2 forces g=f

This question cannot be calculated using f=un.

Because static friction is different from kinetic friction.

Balanced by the force in the vertical direction, the static friction force is always equal to the gravitational force.

The horizontal equilibrium force comes from the different parts of the hand, specifically the pressure of the left and right or the corresponding parts of the hand on the bottle. Let's say, if you only have your hand touching one side of the bottle, can you pick it up? Therefore, we need to hold the bottle and rely on the corresponding parts of the left and right parts of the bottle to balance.

Unchanged gets bigger.

The bottle is always at rest, according to the knowledge of equilibrium: the static friction of the bottle by the hand and the gravity of the bottle itself are a pair of balancing forces. When the bottle's own gravity changes, the amount of static friction changes.

C. Test question analysis: the bottle remains stationary, the force is balanced, the force analysis of the bottle, the vertical direction is subject to gravity and static friction, the two forces are balanced, so the static friction is equal to gravity; After the grip force is doubled, the bottle can not fall down, it still remains stationary, gravity and static friction in the vertical direction are still balanced, and the static friction is still equal to gravity, so the size remains the same, the direction is upward, c is correct, comments: static friction has nothing to do with pressure, it changes with the change of external force, here the grip force becomes larger, but the maximum sliding friction becomes larger, and the object is subject to static friction, so the static friction remains unchanged

a. The bottle remains stationary, the force is balanced, the force analysis of the bottle, the vertical direction is subject to gravity and static friction, and the two forces are balanced, so the static friction is equal to the gravity, and the direction is upward;

After the grip force is doubled, the bottle can not fall even more, it still remains stationary, the gravity and static friction in the vertical direction are still balanced, and the static friction is still equal to gravity, but the maximum static friction between the hand and the bottle increases, so A is wrong.

B. Analyzed by A, B is correct.

C. Analyzed by A, C Error.

d. Analyzed by A, D is wrong.

Therefore, b

Because it is still in the water, the less water in the bottle, the greater the buoyancy, the more water, the smaller the buoyancy, if it is filled with water, the bottle is suspended in the water, and the opposite is the case when it is still in the air (if you let go in the air, the bottle will fall, if you let go in the water, the bottle will float; If the weight of the bottle is ignored, if it is empty in the air, then the bottle is suspended in the air, and if the water is filled with water, the bottle is suspended in the water).

So A is wrong, there should be a vertical downward friction to counteract the buoyancy. D Yes, the more water there is, the heavier it gets, and finally when it is filled with water, it is suspended, and it is still when you let go.

The tightness of the hand and the increase of the pressure of the hand on the bottle can only indicate that the potential of the friction provided by the hand to the bottle has increased, but the specific size of the friction force is only the same as the buoyancy of the bottle.

So B is wrong, C is wrong.

a Right. The greater the mass of the oil in the bottle, the greater the gravitational force received, and the greater the friction required to keep it from falling, so the positive pressure must be increased if the coefficient of friction remains the same.

b False. This is the static friction force that does not increase due to the increase of positive pressure when the object is relatively stationary, but is equal to the magnitude of the force that gives the object a relative tendency to motion.

c Right. The reason is the same as b

d Right. The maximum static friction is equal to the coefficient of static friction multiplied by the positive pressure.

c.The bottle is stationary. So in the vertical direction the bottle is balanced by force, so the total gravity = the static friction experienced by the bottle, because the gravity is not the same, so the friction is not the same. Choose C

Hold a bottle in your hand, the mass of the bottle does not change, and the gravity does not change

If the holding force is increased, the bottle is also stimulated to be static in the hand, and the vertical direction of the bottle is subjected to the friction of the vertical upward stove and the vertical downward gravity, and the gravity remains unchanged, so the friction remains unchanged

Therefore, choose D

There is a pair of equilibrium forces in the vertical direction, namely: the vertical downward gravitational force and the vertical upward static friction force

So:

Select C

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The static friction of the hand against the bottle is equal to the gravitational force experienced by the bottle.

In the vertical direction, the bottle is at rest and must be affected by the equilibrium force. The vertical upward frictional force and the vertically downward gravity force are a pair of balancing forces.

Hold the bottle with your hand, the bottle is still in your hand, the following statement is correct A is right, the rest is balanced by the force, the friction is equal to the gravity of the bottle B is wrong, the reason is the same as a

c Yes, the maximum static friction is proportional to the positive pressure.

D is false, and the reason is the same as A