1. Why do these crates just sit there? Why don’t they start moving?

2. Why will the ball stop rolling?

3. Forces

4. Force: A push or a pull – Newtons (N)

5. Are there forces acting on the crates? GravitySurface

6. What is the sum of the (net) forces? Zero

7. What forces act on the ball? Gravity Surface Friction

8. What is the net force on the ball? Friction

9. Why do these crates just sit there? Why don’t they move? No Net Force

10. Why will the ball stop? A Net Force

11. What is the net force on the wagon? Zero How many forces are acting on the wagon?

12. What is needed to change the motion of an object? A Net Force

13. Is the net force zero? Almost

14. Force Addition Forces add like displacements. They are vectors. One plus one can equal anything from zero to two depending on the direction.

15. Friction Forces There are four general types of friction – Static – Sliding – Rolling – Fluid

16. Force of Gravity All matter attracts all other matter 1642 to 1720 Isaac Newton

17. Force of Gravity 1665 Law of Gravity Calculus Laws of Motion

18. Universal Law of Gravity

19. Weight vs. Mass Weight: a measure of the force of gravity on an object Mass: – How much stuff an object is made of – How much an object resists a change in motion Inertia

20. When you first jump out of the plane people Gravity a = 9.8 m/s 2

21. As you fall you go faster and faster Gravity The Air Resistance Force grows larger until it is the same size as the Gravity Force Air Resistance

22. Which makes the net force get smaller Net Force

23. And the acceleration zero a = 0

24. What happens when something falls on the Moon? Moon Lab

25. The Laws of Motion If no net force acts on an object, the object will not change its motion A net force causes an object to accelerate – Change magnitude and/or direction

26. Example A man pushes on a refrigerator of mass 250kg with a force of 500N. – A) What is its acceleration? – B) What is its speed after 2s?

27. Third Law For every action there is an equal and opposite reaction Forces always come in pairs. They are equal in size, opposite in direction but do not cancel because they are on different objects

28. Third Law The runner pushes on the starting blocks, they push back on the runner

29. Momentum

30. I do not know what I may appear to the world, but to myself I seem to have been only like a boy playing on the sea-shore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me