How are gravity, weight and normal force related

Gravitation

• It’s the force that acts on a body, attracting it towards a second body. Usually the second body is the Earth.

$$F_g=mg$$

Weight

• Weight is the magnitude of net force one would need to apply to prevent a body from freely falling.
• This is the same as the gravitational force, but in the opposite direction. $W=-mg$

Normal Force

• When a body is pushed against another body, each of the bodies exert some force on the other body.
• This force is called the normal force and it is perpendicular to the surface of the exerting body.

Example:

• When an box is kept on a table the body is pulled toward the earth with $mg$.
• The amount of force required to hold this up would be $mg$.
• The table holds up the body without breaking ⇒ the normal force exerted by the table on the box is $mg$.