1. I NERTIA AND N EWTON ’ S F IRST L AW OF M OTION

2. DEMO TIME History of Physics: http://vimeo.com/69381331

3. ARISTOTLE Lived in Greece Born 384 BC Died: 322 BC Believed that unequal masses Reach the ground at different time All movement required forces Proper state was of rest – all objects will eventually come to rest. Stood for 2000 years

4. GALILEO Lived in Italy Born: 1564 Died 1642 Believed unequal masses fell at the same time

5. G ALILEO ’ S THOUGHT EXPERIMENT Galileo observed objects return to original position regardless of incline Therefore, object’s “natural” state is not of rest They resist changes in motion - inertia

6. Observed that inclines change velocity The smoothness of surface directly effected motion With no friction (surface or air), how does speed change on a level surface?

7. I NERTIA A property of matter that causes an object to resist changes in its state of motion; it is directly proportional to the mass of the object. Inertia = laziness = an object’s resistance to change

9. N EWTON ’ S FIRST LAW / LAW OF INERTIA : Objects at rest or moving with a constant velocity maintain their state of rest or constant velocity unless acted upon by an external, unbalanced force.

10. I NERTIA AND CAR CRASHES This law of inertia helps us to understand the principles behind using seatbelts and air bags. Once an object is moving, it tends to keep moving at a constant velocity because of its inertia. Air bags and seatbelts help to slow us down safely.

11. E XAMPLES OF I NERTIA pulling tablecloth out from under dishes card and glass Coin into cup

12. N EWTON ’ S S ECOND

13. S HOW M E State Newton’s first law of motion

14. N EWTON ’ S SECOND LAW The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object. F net = ma Force: Any influence that causes an object to undergo a certain change, either concerning its movement, direction, or geometrical construction.

15. D ERIVING THE N EWTON The unit of Force is the N (Newton) N = kgm/s

16. F NET = VECTOR SUM OF ALL FORCES

17. E XAMPLE : A mass of 6 kg is accelerated to 3.2 m/s 2. What force was applied? A 14 N [left] force is applied to a 5 kg mass. What is the acceleration? A force of 250 N [right] is applied to an object that causes it to accelerate to 4.5 m/s 2. What is the mass of the object?

18. P RACTICE In Motion: Newton’s Laws Practice Booklet Pages 3-4

19. S HOW M E What is Newton’s Second Law?

20. N EWTON ’ S THIRD L AW

21. For every action there is an equal and opposite reaction. http://www.youtube.com/watch?v=JGO_ zDWmkvk

22. M ASS VS. W EIGHT Mass never changes Weight is the force of gravity acting on a mass. Measured in Newtons (N) Weight = (mass) x (acceleration due to gravity) W = mg

23. Sally has a mass of 60 kg. What is her weight on Earth? What is her mass on Mars? What is her weight on Mars? What is her mass on Jupiter? What is her weight on Jupiter?

24. Joshua weighs 100 N on Earth. He wants to bulk up so he goes to the Venus. Is this a good idea? 1) What is his mass on Earth? 2) What is his mass on Venus? 3) What will his weight be on Venus?

25. R ECAP N EWTON ’ S L AWS http://www.youtube.com/watch?v=mn34mnnDnKU

26. MOMENTUM

27. Which scenario will cause the bigger dent in your car? A sports car travelling at 50 km/h crashes into your car? A tank travelling 50 km/h crashes into your car?

28. The tank will cause more damage because it has more momentum

29. Which scenario will cause the most damage to you? A 5 g bullet travelling at 30 m/s hits you in the leg? (fired from a gun) Your friend tosses you a 5 g bullet at a speed of 1 m/s.

30. Obviously the bullet fired from the gun will cause you greater pain. In this case the bullet from the gun has a greater momentum.

31. Momentum depends on two factors, mass and velocity p = mv p = momentum m = mass v = velocity momentum is a vector (it has magnitude and direction)

32. E XAMPLES Example: Calculate the momentum of a 1000 kg car travelling at 6m/s to the right

33. C ONSERVATION OF STUFF

34. COLLISION EXAMPLE A 1000 kg car travelled at 6 m/s to the right collides with a 1500 truck travelling at 5 m/s to the left. 1) What is the momentum of the car? 2) What is the momentum of the truck 3) What is the total momentum of the system before the collision? 4) What is the total momentum of the system after the collision ?

35. T HE ONLY RULE Energy is always conserved The total amount of energy before an event will be equal to the energy after an event This concept applied to momentum MOMENTUM BEFORE A COLLISION = MOMENTUM AFTER A COLLISION

36. I NELASTIC COLLISIONS Inelastic = objects collide and stick together Example: A 1000 kg car travelled at 7 m/s to the right collides with a 2000 kg semi travelling at 5 m/s to the left. If the collision in inelastic, 1) What is the total momentum of the system after the collision 1) What is the velocity of the system after the collision

37. ELASTIC COLLISIONS Elastic = the objects do not stick together Example: Jenny (mass = 80kg) is skating with a velocity of 2m/s to the right. She runs into Justice (mass=70 kg) who was too busy texting to move (thus he was stationary) 1) What is the total momentum of the system after the collision? 2) What is the momentum of Jenny after the collision? 3) What is the momentum of Justice after the collision?

38. HOMEWORK In Motion: Newton’s Laws Practice Booklet: Pages 5-6 ***Add in*** What is Paul’s final velocity? 7) A car with mass 1500 kg, travelling at 10m/s collides inelastically into a stationary smart car (m= 500 kg). a) What is the initial momentum of both cars b) What is the initial momentum of the system? c) What is the final momentum of the system? d) What is the final velocity of the system after the collision? Paul (mass = 90kg) is running 5 m/s [Right] and collides with Laura (mass = 70 kg) running 5 m/s [Left]. After the collision Laura is moving with a velocity of 2 m/s [right]

39. I MPULSE

40. I MPULSE = I Objects in motion stay in motion unless you apply a force against the motion for a period of time The greater the momentum of an object, the harder it is to stop the object’s motion. To stop an object with a large momentum, you will need to either apply a large force or apply a force for a long period of time

41. F ANCY DERIVATION Inpulse causes a change in momentum I = Δp = p final – p initial I = F net Δt

42. Example: In football, the defensive player applies a force for a given amount of time to stop the momentum of the offensive player with the ball. Impulse causes a change in momentum.

43. EXAMPLES A water skier lets goof the tow rope and coasts to a stop. If the water exerts an average force of 280 N on her, and she stops in 5.0 seconds, what is the impulse that the water exerts on the skier?

44. A pool ball of mass 0.125kg rolls toward the cushion at 3 m/s and bounces back at 2 m/s a) What is the initial momentum of the ball? b) What is the final momentum of the ball? c) What is the change in momentum of the ball d) What is the impulse of the ball?

45. T RY IT OUT In Motion: Newton’s Laws Practice Booklet Pages 6-7