What are the forces?

Question

If there is an apple sitting on a table, what are the forces acting on it? I know that there is gravity pushing in a downwards direction. I also know that there is a second force pushing up on it. Would that be the table exerting a force on the apple in an upwards direction?

Answer 1

Because of the gravitational force the apple should go down. But it is not going down. Therefore we infer that there must be an upward force equal to the gravitational force.

The apple is exerting a force on the table. If we call it as action,then as per Newton's third law there must be an equal but opposite force ( reaction) on the apple by the table. This we call it as normal reaction force.

Therefore there are two forces acting on the apple.

1. The gravitational force acting down ward.
2. The normal force given by the table on the apple.

These two forces need not be equal in magnitude.

But since the apple is at rest we infer that these two forces are equal and opposite and hence the net force on the apple is zero.

Imagine that the table top is made of thin paper. Then the paper will depress down and due to elasticity the paper tries to regain its original shape and hence gives an upward force. this force is the normal reaction. The motion of the apple depends on the net force on the apple.

Answer 2

There are only two forces,

Gravity (which attempts to accelerate it down)

The Normal force (which produces an exactly opposite force in the upwards direction, the normal force is actually a fake force. it's really a combination of the electro-weak forces which are preventing the atoms of the apple from penetrating the potential barriers of the atoms in table).

Answer 3

Hi. There are several. Friction, momentum, inertia, acceleration (opposing gravity). The table exerts acceleration of 1 g.

Answer 4

It is the electromagnetic force of the atoms of the table that is pushing up on the apple.