1. NEWTON’S LAWS

2. NEWTON’S 1st LAW

3. INTRODUCTION
The ancient Greeks, in about 300 BC, were said to have believed that objects have natural resting places, and objects will move towards those places. For example, a rock falls to the ground.

4. INTRODUCTION
A puff of smoke rises into the air.

5. INTRODUCTION
The Greeks also thought that once an object was in motion, that an outside force was needed to keep it moving.

6. INTRODUCTION
In the early 1600’s, an Italian astronomer, Galileo Galilei questioned the idea that force is needed to keep an object moving. He suggested that once an object is moving, no push or pull is needed to keep it moving.

7. INTRODUCTION
He said that force is only needed to change the motion of an object. But whether it is moving or at rest, every object resists any change to its motion.

8. INTRODUCTION
This resistance is called inertia. Inertia means that all objects have a tendency to resist a change to their motion.

9. INTRODUCTION
Galileo’s ideas paved the way for the English mathematician Sir Isaac Newton. Newton discovered the three basic laws of motion in the 1680s. The first of his three laws restates Galileo’s idea.

10. INTRODUCTION Newton’s first law of motion states:
An object at rest will stay at rest, and an object in motion will stay in motion, unless it is acted upon by an outside force.
Newton’s 1st law is also called the law of inertia.

11. INTRODUCTION
Inertia explains many common events. For example: If you are in a car that suddenly stops, inertia causes you to continue to move forward.

12. INTRODUCTION
Passengers in a moving car have inertia. To prevent people from flying out of the car, a force is required to change their motion. That force is exerted by the safety belt. If the safety belt is not worn, that force may be exerted by the windshield instead!

13. NEWTON’S 2nd LAW

14. INTRODUCTION
You decide to take your two little brothers for a ride in a wagon. You find them yelling “Faster, faster!” Soon you are out of breath.

15. INTRODUCTION
You set in the wagon and one of the boys tries to pull you in the wagon, but he can’t get it going very fast.

16. INTRODUCTION
How can you increase the acceleration of the wagon?

17. INTRODUCTION
One way would be to change the force. Acceleration and force change in the same way. An increase in force results in an increase in acceleration. So both boys needs to pull you.

18. INTRODUCTION
F = ma
Another way is to change the mass. Acceleration and mass change in opposite ways. This means that an increase in mass causes a decrease in acceleration. It also means that a decrease in mass causes an increase in acceleration.

19. INTRODUCTION
Try pulling only one boy instead of two to go faster.

20. INTRODUCTION Less mass = more speed More mass = less speed
Newton’s second law explains how force, mass, and acceleration are related. Basically to make an object move faster you apply more force, or you reduce the mass. So as mass increases, acceleration decreases, and as mass decreases acceleration increases. The second law is also called the law of acceleration.
Less mass = more speed
More mass = less speed

21. NEWTON’s THIRD LAW

22. INTRODUCTION
If you pushed against a wall, what would happen?

23. INTRODUCTION
What would happen if you had skates on?

24. INTRODUCTION A
What would happen if you pushed harder?

25. INTRODUCTION
For every force there is an equal and opposite force.

26. INTRODUCTION
Example: When you walk, your foot pushes on the ground and the ground pushes back on your foot. The result is that you move forward.

27. INTRODUCTION
Forces always happen in pairs. There is never a single force acting by itself. Something is always acting against any force. We call this action reaction pairs. Also, the two forces are exactly the same magnitude, just in opposite directions.

28. INTRODUCTION
Important note: When objects act and react, it happens at the exact same moment. Just because it says action or reaction doesn’t mean that one happens and then the other happens. Like this ball hitting the bat. The action and the reaction happen at the same time.

29. OBJECTIVE
Memorize Newton’s 3 laws of motion.

30. VOCABULARY Inertia – resistance to a change in motion.
Mass – How much material is in something.
Acceleration – Change in speed or direction.

31. IN QUESTION
Fred spends most Sunday afternoons at rest on the sofa, watching pro football games and consuming large quantities of food. What effect (if any) does this practice have upon his inertia?
Fred’s inertia will increase as his mass increases.

32. NOTES Newton’s 3 laws explain how and why objects move.
1st law – objects in motion stay in motion, objects at rest stay at rest unless acted on by an unbalanced force.
It’s also called the Law of Inertia.

33. NOTES
2nd law - for any force, the acceleration of an object is proportional to the net force and inversely proportional to the mass of the object.  (As mass increases acceleration decreases and vice versa.)
F = ma force = mass x acceleration
It’s also called the Law of Acceleration.

34. NOTES
3rd law – for every action there is an equal and opposite reaction.
Action /reaction pairs happen at the same time.
Forces always work in pairs.
It’s also called the Law of Action/Reaction.

35. OUT QUESTION
While driving down the road, an unfortunate bug strikes the windshield of a bus. The bug hit the bus, and the windshield hit the bug. Did the bug strike the bus with more force, or did the bus strike the bug with more force?
They strike with the same amount of force.