Ch. 3

1
Ch. 3 4Motion Forces

• VI. Action and Reaction
• Newtons Third Law
• Momentum
• Conservation of Momentum

2
A. Newtons Third Law

• Newtons Third Law of Motion
• When one object exerts a force on a second
  object, the second object exerts an equal but
  opposite force on the first.

3
A. Newtons Third Law

• Problem

• How can a horse pull a cart if the cart is
  pulling back on the horse with an equal but
  opposite force?

• Arent these balanced forces resulting in no
  acceleration?

4
A. Newtons Third Law

• Explanation

• forces are equal and opposite but act on
  different objects
• they are not balanced forces
• the movement of the horse depends on the forces
  acting on the horse

5
A. Newtons Third Law

• Action-Reaction Pairs

• The hammer exerts a force on the nail to the
  right.
• The nail exerts an equal but opposite force on
  the hammer to the left.

6
A. Newtons Third Law

• Action-Reaction Pairs

• The rocket exerts a downward force on the exhaust
  gases.
• The gases exert an equal but opposite upward
  force on the rocket.

7
A. Newtons Third Law

• Action-Reaction Pairs

• Both objects accelerate.
• The amount of acceleration depends on the mass of
  the object.

• Small mass ? more acceleration
• Large mass ? less acceleration

8
JET CAR CHALLENGE

• CHALLENGE
• Construct a car that will travel as far as
  possible (at least 3 meters) using only the
  following materials.

• scissors
• tape
• 4 plastic lids
• 2 skewers

• 2 straws
• 1 balloon
• 1 tray

How do each of Newtons Laws apply?