WeightA Force Caused by Gravity

If we apply Newton’s 2nd Law to objects accelerating due to gravity

FG = mg

FG – force of gravity, commonly called weight

2nd Law and Gravity

When an object is resting on the surface of Earth, the force of gravity is still acting, even though the object is not moving

Must be another force acting to balance the force of gravity, called the Contact Force

When the contact force acts perpendicular to the surface it is referred to as the Normal Force (FN)

Normal

A 3.5kg box is resting on the floor. Draw the free body diagram

Example

A 10.0kg box is resting on a tablea) draw the free body diagramb) now it is pushed down with a force of 40N. Draw the free body diagram.c) now it is pulled up with a force of 40N. Draw the free body diagram.

Ex

What happens when the box in the previous problem is pulled up with a force of 100N?

Ex.