FORCE & FRICTION

Force: push or pull all forces have size and direction measured in Newtons (N)

Science Pushes and Pulls, but it

NEVER Sucks!

An object willspeed up,

slow down,or turn

Only if something is pushing or pulling on it.

Usually, more than one force is acting on an object.

Net Force: Combination of all forces on an object

Determines motion of object (similar to total velocity)

Combining Forces

Forces in the Same Direction

When forces act in the same direction, you add the forces to determine the net force. The net force will be in the

same direction as the individual forces.

25 N20 N

Net Force25 N + 20 N = 45 N to the right

Forces in Different Directions

When two forces act in opposite directions,subtract the smaller force from the larger force. The net force will be in the same direction as the larger force.

35 N

20 N

Net Force35 N – 20 N = 15 N Up

Balanced and Unbalanced Forces

This is ZERO fun!!!

Balanced Force: Net Force = ZERONo CHANGE IN MOTION

12 N 12 N

Balanced and Unbalanced Forces

Unbalanced Force: Net Force = NOT zero CHANGE IN MOTION

Eat it!!!

Don’t wipe that on

me!

12 N

20 N

BEWARE OF THESE FORCES!

What force was missing in the video?

Friction: slows motion, can cause moving objects to slow down and stop

FRICTION—What a Drag!As force increases, friction increases.

The rougher the surface is, the greater the friction is.

Kinetic Friction: “moving”, friction between moving surfaces

Rolling and Sliding FrictionUnbalanced Force—Net Force Doesn’t = Zero

Static Friction: “not moving”Balanced Force—Net Force = ZERO

Types of Friction