THE ACCELERATION OF AN OBJECT IS DEPENDENT UPON TWO VARIABLES - THE NET FORCE ACTING UPON THE

OBJECT AND THE MASS OF THE OBJECT.

Newton’s Second Law of Motion

Law of Acceleration, Force. and Mass

Acceleration, Force, and Mass

Newton determined that Acceleration is affected by Force directly and Mass inversely. So….

Check for Understanding

How can both of these objects under free fall conditions accelerate at the same rate?1. The elephant has

more force applied to it.

2. The boy has more force applied to him.

3. The forces on the objects are the same.

Newton’s Third Law of Motion

Law of Action-Reaction

Newton’s Third Law of Motion

If one object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction on the first object

“For every action there is an equal but opposite reaction”

Action – Reaction Pairs

Do Action – Reaction Forces “Balance”?

Action – Reaction forces do not “balance” out because they are acting on 2 different objects – therefore, can cause a change in motion!

Detecting Motion

You can’t always detect motion when paired forces are in action.

If one of the pairs is much more massive, you will only see the less massive object move

Example – When you push down on the Earth, you won’t see the Earth move, only you jumping in the air

Force

Unbalanced

Objects motion changes in the same direction as the force.

Fnet≠0

a≠0

Balanced

Object remains at rest or

uniform motion.

Fnet=0

a=0

Summation Equations

Forces are often represented using Free Body Diagrams so we can quickly determine if there is an unbalanced force present.

Balanced or Unbalanced?

Use a summation equation to determine if forces are balanced or unbalanced.

FNET=F1+F2+F3+F4….

Check for Understanding

Write the summation equation for each of the following. Which has the greatest net force?