1. CHAPTER 6
NEWTON’S THIRD LAW

2. FORCE A FORCE IS A PUSH OR A PULL IT IS PART OF AN INTERACTION
IT DOES NOT EXIST ALONE; IT MUST EXIST IN PAIRS

3. NEWTON’S THIRD LAW
WHENEVER ONE OBJECT EXERTS A FORCE ON A SECOND OBJECT, THE SECOND OBJECT EXERTS AN EQUAL AND OPPOSITE FORCE ON THE FIRST OBJECT.

4. WHAT ARE THE FORCES?
ACTION FORCE
REACTION FORCE

5. NEWTON’S LAW RESTATED
TO EVERY ACTION THERE IS ALWAYS AN EQUAL OPOSING REACTION

6. DOES A STICK OF DYNAMITE CONTAIN FORCE?
NO! FORCE IS NOT SOMETHING AN OBJECT HAS, LIKE MASS. FORCE IS AN INTERACTION BETWEEN ONE OBJECT AND ANOTHER.

7. A CAR ACCELERATES ALONG A ROAD
A CAR ACCELERATES ALONG A ROAD. STRICTLY SPEAKING, WHAT IS THE FORCE THAT MOVES THE CAR?
THE ROAD! THE ROTATING TIRES PUSH BACK ON THE ROAD AND THE ROAD PUSHES FORWARD ON THE TIRES.

8. IDENTIFYING ACTION/REACTION
ACTION: OBJECT A EXERTS A FORCE ON OBJECT B.
REACTION: OBJECT B EXERTS A FORCE ON OBJECT A.

9. WE KNOW THAT EARTH PULLS ON THE MOON
WE KNOW THAT EARTH PULLS ON THE MOON. DOES THE MOON ALSO PULL ON THE EARTH? IF SO, WHICH PULL IS STRONGER?
YES! THEY PULL EQUALLY.

10. ACTION AND REACTION ON DIFFERENT MASSES
F=MA
IF THE FORCES ARE EQUAL, BUT THE MASSES ARE DIFFERENT THE ACCELERATION WILL VARY.

11. HOW DOES A HELICOPTER FLY
THE BLADES PARTICIALLY FORCE AIR DOWN(ACTION) THE AIR FORCES THE BLADES UP. WHEN THE UPWARD REACTION (LIFT) IS GREATER THAN THE WEIGHT THE HELICOPTER FLIES.

12. CAN YOU IDENTIFY THE ACTION AND REACTION FORCES.
FIRST IDENTIFY THE PAIR OF INTERACTING OBJECTS INVOLVED.
SECOND IDENTIFY ONE FORCE AS ACTION AND THE OTHER AS REACTION.

13. DO ACTION/REACTION FORCES CANCEL EACH OTHER
IF THE INTERACTION IS BETWEEN A SYSTEM AND SOMETHING EXTERNAL THE FORCES DO NOT CANCEL
IF THE INTERACTION IS WITHIN THE SYSTEM THE ACTION/REACTION FORCES DO CANCEL.

14. QUESTION
SUPPOSE A FRIEND WHO HEARS ABOUT NEWTON’S THIRD LAW SAYS THAT YOU CAN’T MOVE A FOOTBALL BY KICKING IT BECAUSE THE REACTION FORCE BY THE KICKED BALL WOULD BE EQUAL AND OPPOSITE TO YOUR KICKING FORCE. THE NET FORCE WOULD BE ZERO, SO NO MATTER HOW HARD YOU KICK, THE BALL WOUN’T MOVE! WHAT DO YOU SAY TO YOUR FRIEND?

15. SOLUTION
IF YOU KICK A FOOTBALL, IT WILL ACCELERATE. YOUR KICK ACTS ON THE BALL. NO OTHER FORCE HAS BEEN APPLIED TO THE BALL.THE REACTION FORCE ACTS ON YOUR FOOT AS IT MAKES CONTACT WITH THE BALL. SO THE FORCES DO NOT CANCEL EACH OTHER.

16. QUESTION
DOES THE HORSE PULL THE WAGON OR DOES THE WAGON PULL THE HORSE?
WHY DOES THE CART MOVE?

17. SOLUTION
THE WAGON DOES PULL BACK EQUAL AND OPPOSITE ON THE HORSE, BUT IN ADDITION TO THAT THE HORSE IS PUSHING ON THE GROUND AND THE GROUND IS PUSHING BACK ON THE HORSE WHICH IS WHAT ALLOWS THE HORSE TO MOVE FORWARD PULLING THE WAGON!

18. ACTION EQUAL REACTION
AN OBJECT CAN ONLY REACT BY THE MAXIMUM AMOUNT OF FORCE IT CAN ENDURE.