When will a Normal Force be equal to the product of mass and gravity? and Why?

Question

Thank you, sorry for the bad english

When will Fn = Mg ? thanks

Answer 1

what do you mean by 'normal'??

what do you mean by 'gravity'??

A mass when placed in a gravitational field will experience a force equal to its mass times the magnitude of the field. The direction of the force will be the same as the direction of the gravitational field. A gravitational field being an example of a vector field.

Answer 2

I think that by normal force, you mean the reaction that a hard surface put on an object in the direction normal to the surface of contact, like when you push on a vertical wall, the normal force is the horizontal force with which the wall reacts to your push to stop your hand from penetrating it.

Since you mention gravity and mass, this normal force must be the reaction to a weight. Well, that normal force is equal (and of opposite direction) to the the weight mg when the surface which the body rests on is a fixed horizontal plane. If that surface is an incline making an angle α with the horizontal, then the normal force is equal (and in opposite direction) to the projection of mg on the normal of the incline: Fn = mgcosα.

If the horizontal surface said above is moving up or down with acceleration a, the normal force will be less or more than mg by an amount ma depending on the direction of the acceleration and of the motion.

Side note

The use of the term normal force is correct in English, but in other language, like in French, people prefer more precise terminology. They call Fn normal component of the reaction.