Net Forces

Force

• A push or pull on an object

• Able to change the motion of an object

• Gravity, friction, and air resistance are three

common forces on Earth

Air Resistance

Friction

Gravity

Net Force

•The overall force exerted on an object; measured in
Newtons (N)

•If the net force is 0, then a change in motion will not
occur

•NOTE: This does not mean that the object is stationary.

•If the net force is greater than 0, then a change in
motion will occur

5 N + 7 N = 12 N

Net Force

Net Force

•Subtract the forces if the arrows are pointed
toward each other or pointed away from each
other

•Add the forces together if the arrows are all
pointed the same direction

How to calculate net force from a picture or diagram

OR

OR

Practice problem(s) on checkpoint at the end.

Balanced Forces

•Equal forces that do not cause a change in an
object’s motion (Net Force = 0 Newtons)

•The net force on an object must be calculated in
order to determine if it is balanced or unbalanced

50 N

50 N

Balanced Forces

•Equal forces that do not cause a change in an
object’s motion (Net Force = 0 Newtons)

•The net force on an object must be calculated in
order to determine if it is balanced or unbalanced

50 N

50 N

50 N – 50 N = 0 N
BALANCED

Balanced Forces Examples

• A cell phone resting on the counter

• Tying an arm wrestling match

• A picture hanging on the wall

• Any object with no motion

• Any object moving at a constant speed

Forces are balanced when the net force = 0 Newtons

Unbalanced Forces

•Unequal forces that cause a change in an
object’s motion

•Cause a change in speed and/or direction of an
object – moves the direction of the greater force

100 N

50 N

Unbalanced Forces

•Unequal forces that cause a change in an
object’s motion

•Cause a change in speed and/or direction of an
object – moves the direction of the greater force

100 N – 50 N = 50 N

100 N

50 N
UNBALANCED

Unbalanced Forces Examples

• A football player tackling a quarterback

• Pushing a lawnmower across the yard

• A skydiver falling toward the ground

• Any object that is speeding up, slowing down,

or changing direction (accelerating)

Forces are unbalanced when the net force

does not equal 0 Newtons

Checkpoint

• 5 checkpoint questions

• Discuss each question with a partner

• Write a complete answer to each question on

your notes page