1. Day 2 1-5-11 Topic: Newton’s 3rd Law
Objective: I will recognize force pairs.
Science Starter: Draw a simple sketch & explain why the skater moves forward.
The skater moves
forward because . . .
the GROUND PUSHES
BACK on the SKATER with
an EQUAL and OPPOSITE
REACTION FORCE

2. Identifying ACTION and REACTION forces
FORCE PAIR Guidelines
1. Forces ‘come’ in PAIRS
2. Each force has the same strength (=).
3. Force Pairs act in opposite directions.
4. Force Pairs act on different objects.
EXAMPLE: The Skateboarder
ACTION FORCE: on the GROUND by the FOOT
REACTION FORCE: on the FOOT by the GROUND

3. HOMEWORK REVIEW
Who wins this contest?
Imagine a skateboard contest between Newton and an elephant. They can only push against each other, not against the ground. The fastest one wins. The elephant knows it is much stronger and pushes off Newton with a huge
force thinking it will surely win. But who does win?

4. Action and Reaction forces. 2. Given: One force in Newtons; 500 N down
EXAMPLE:
A woman with a weight of 500 N is sitting on a chair. Describe an action-reaction pair of forces.
1. Looking for:
Action and Reaction forces.
2. Given:
One force in Newtons; 500 N down
3. Relationships:
Action-reaction forces are equal and opposite, and act on different objects.
4. Solution:
ACTION: The 500N force on the chair by the woman
REACTION: The EQUAL 500 N force on the woman by the chair

5. ACTION FORCE
A baseball player hits a ball with a bat. Describe an action-reaction pair of forces.
LOOKING FOR:
GIVEN:
RELATIONSHIP:
SOLUTION:
REACTION FORCE
Force Pairs
A bat hits a ball
Force Pairs are EQUAL & OPPOSITE
& act on DIFFERENT objects
ACTION FORCE: Force on the ball by the bat
REACTION FORCE: Force on the bat by the ball

6. The force of the bat on the ball accelerates the ball
The force of the bat on the ball accelerates the ball. The force of the ball on the bat (reaction) slows down the swinging bat (action).

7. List one action / reaction pair shown in the picture below.
Why don’t action and reaction forces cancel?
L: Force Pairs G: R: S:
Write this
Q & A
please
ANSWER: The FORCES are acting on DIFFERENT OBJECTS

8. List action/reaction force pairs
L: Force Pairs G: R: S:

9. The players foot kicks the ball.
L: Force Pairs G: R: S: