As Level Physics

1. As Level Physics Mechanics

2. The Key concepts

3. Vectors • These have direction as well as size (Magnitude) • They include • Forces,Velocity,weight,Displacement,acceleration etc

4. Scalars • These only have size or magnitude • They include • Energy, speed, mass, distance etc.

5. Addition of Vectors • You can add vectors by using a parallelogram:- Resultant

6. Components • A component is part of a force that has been split into two e.g. a Horizontal or vertical component.

7. Splitting a force into components • What is the horizontal component of F? F A

8. Horizontal component of F = F Cos A F F A A Hotizontal Component = F Cos A

9. Splitting a force into components • What is the Vertical component of F? F A

10. Vertical component of F = F Sin A Vertical Component = F Sin A F F A A

11. Two components or forces at right angles can be added using Pythagoras

12. E.g. Adding Forces F and P R F F P P

13. R2 = P2 + F2 Tan A = F/P R F F A P P

14. The Centre of Mass • This is where all of the mass of an object appears to act. • E.g. If an object is balanced it will be in line with the centre of mass of the object.

15. The Centre of Gravity • This is where all of the weight of an object appears to act. • E.g. If an object is balanced it will be in line with the centre of gravity of the object.

16. Balanced Centre of mass Balanced

17. Not Balanced! Centre of mass

18. Moments • This wont take very long!

19. Moment = Force x Perpendicular distance (of the line of action) F Hinge D Moment = F x D

20. Moment = Force x Perpendicular distance (of the line of action) F A Hinge D Moment = F (SinA) x D

21. Example of moment 35N 40o Hinge 30m Moment = F SinA x D = 35 (Sin40) x 30 =675 Nm

22. Velocity • What is it? • In words and equation!

23. Velocity Is the rate of change of displacement It is a vector (speed is scalar) V = Change in s = s Change in t t

24. Direction of velocity • The object is travelling in an ellipse The arrows show the direction of the Velocity

25. Acceleration • What is acceleration • In words and equation!

26. Acceleration Is the rate of change of velocity It is a vector A = Change in v = v Change in t t

27. Direction of acceleration • An object is travelling in a circle: What is the direction of the acceleration?

28. Direction of acceleration • The object is travelling in a circle The arrows show the direction of the acceleration I.e. Towards the centre!

29. Velocity and acceleration for projectile • Acceleration is Always………….? • The velocity is at a T……… to the path. • The Horizontal velocity is C………… • The vertical velocity is C………… • The shape is p………..

30. Velocity and acceleration for projectile • Acceleration is Always downwards • The velocity is at a Tangent to the path. • The Horizontal velocity is Constant • The vertical velocity is Changing (due to gravity) • The shape is Parabolic

31. Shape of parabola • Small arrows velocity (tangent to curve) • Large arrows acceleration (always down)

32. Displacement time graph Displacement D C B Time A What is happening with each section?

33. Displacement time graph • Setion A-B is straight so steady velocity • Section B-C is horizontal so no velocity • Section C-D is getting steeper so it is accelerating. • The steepness or gradient of a displacement time graph is the velocity.

34. Displacement time graph Displacement D Accelerating Constant velocity C B Stationary Time A

35. Velocity Time Graph • What does the gradient tell us? • What about the area under the graph?

36. Velocity Time Graph • The gradient is the acceleration • The area under the graph is the distance travelled • Now look at the following graph and try to work out what is happening in each section

37. Velocity time graph Velocity D C B A Time Area 2 Area 1

38. Gradient of velocity time graph • Section A-B Steep so accelerating • Section B-C Horizontal so steady velocity • Section C-D getting steeper so acceleration getting bigger • THE GRADIENT OF v – t GRAPH IS THE ACCELERATION

39. Gradient of Velocity time graph Velocity Increasing acceleration Steady Velocity D Constant acceleration C B A Time Area 2 Area 1

40. Area under velocity time graph • THE AREA UNDER A VELOCITY TIME GRAPH IS THE DISTANCE (OR DISPLACEMENT) TRAVELLED

41. Velocity time graph Velocity Increasing acceleration Steady Velocity D Constant acceleration C B Time Area 2 = distance from B to C A Area 1 = distance from A to B

42. Momentum • What is this?

43. Momentum • Momentum is the mass multiplied by the velocity • Momentum = m x v • It is a vector and has units Kg m s-1

44. All collisions (or explosions!) • What is always conserved? • (Unless an external force acts)

45. All collisions (or explosions!) • Momentum is always conservedunless an external force acts. • ( a collision is when anything hits anything else!)

46. Elastic and Inelastic • What is the difference between these types of collision?

47. Elastic and Inelastic • With an elastic collision: • BOTH energy and momentum are conserved • With an Inelastic collision: • ONLY momentum is conserved

48. Examples of Elastic and Inelastic collisions • The only really good example of a perfectly elastic collisions is a gas molecule. • A snooker ball gives a good approximation but you can hear energy loss and with an infra red camera you can ‘see’ a hot spot where the collision has occurred!

49. Newton’s Laws of motion • You need to remember them all I will help you a bit! But try to work them out before you carry on!

50. Newton's laws of Motion • 1 Every body con………. • 2 Force equals the ra…….. • 3 For every action ……….