# How do weight and normal cancel each other out when they act on different bodies? [closed]

If a body is kept on the surface then it applies its weight on the surface and the surface applies the normal force on the body. Both are being applied to different bodies, then how do they cancel each other out? And what about other forces like reaction to weight and reaction to normal, how do they affect the body?

• By Newton's 3rd law, the normal force is also equal in magnitude to the force the surface exerts upward on the body. Commented Aug 30, 2023 at 10:44

If the body is kept on the ground => contact surface normal to ground

The body has a = 0

By Newton's Second Law, (for constant mass)

F = ma


As a = 0, F = 0

Only two forces are acting on the body: Weight mg downward, and N vertically upward.

Therefore,

 N-mg = 0


or

N = mg


If the contact surface is not normal to the ground, then it has some acceleration and so the net force will not be zero.

The reactions to normal and weight are not applied on the body, and so they have no effect on the body.

(Weight is the force by which the earth attracts a body. Therefore the reaction to weight is the force by which the body attracts the earth.

Normal is exerted by the surface on the body, and so its reaction is applied by the body on the surface.)

• Thanks, the second last paragraph clears my doubt. Commented Aug 30, 2023 at 10:56
• You're welcome! Commented Aug 30, 2023 at 10:56