1. Motion

2. There are four sections to this…. 1. Speed and Acceleration 2. Forces 3. Work 4. Power Click on the section you want.

3. 1. Speed and Acceleration

4. Speed S D T x S = Speed = distance time D T Speed tells you how fast something is travelling

5. A turtle travels 2 metres in 300 seconds. What speed is it travelling? S D Tx S = D T 2 m 300 s S = 0.007 m/s

6. Distance S D T x S = Speed = distance time D T Distance =speed x time D = S x T

7. A 747 travels from L.A. to Auckland at 700 km/hr. The trip takes 9 hours. How far has the plane travelled? D = S x T S D Tx D = 700 x 9 D = 6,300 km

8. Time S D T x S = Speed = distance time D T Distance =speed x time D = S x T Time = distance speed T = D S

9. A train travels from Wellington to Auckland at an average speed of 110 km/hr. The distance it covers is 550km. How long does the trip take? S D Tx T = D S 550 km 110 km/hr T = 5 hours

10. Units The Standard units are : distance = metres = m time = seconds = s speed = metres per second = m/s Be careful! Look at the units given to you in a question. Convert all parts of a question into the same units. Remember to include the units in your answer.

11. Distance – Time Graphs Time (s) Distance (m) A. Time (s) Distance (m) B. Time (s) Distance (m) C. Constant speed Constant speed (but slower than A) Stationary The gradient of the line is the speed. The steeper the line, the faster the speed!

12. Distance – Time Graphs Time (s) Distance (m) A. Constant speed Time (s) Distance (m) B. Acceleration Time (s) Distance (m) C. Deceleration If the line on a distance – time graph is curved then the object must be changing speed. i.e. getting faster or slower.

13. Acceleration

14. Acceleration = change in speed (m/s) time (s) a s t x Units = m/s s = metres per second squared. = change = m/s 2 = ms -2

15. When the parachutist jumps from the plane his speed downwards goes from 0m/s to 20m/s in just 2 seconds. 20 m/s a = 2s = 10 m/s 2 a s t x His change in speed is from 0m/s to 20 m/s So his acceleration is……. (10 m/s 2 is the acceleration due to gravity)

16. Speed – Time graphs speed m/s Time (s) Increasing speed = acceleration Steady speed = no acceleration Decreasing speed = deceleration

17. Acceleration can also be shown on distance – time graphs: Distance (m) Time (s) Acceleration Deceleration

18. 2. Forces

19. A Force is a: push pull twist

20. Forces may be: Contact Non-contact (field) friction upthrust buoyancy air-resistance magnetic electrical gravitational

21. Forces always act in pairs. Action Reaction

22. ThrustDrag Gravity Buoyancy (Upthrust) If the forces are balanced the object will not change its speed, direction or shape

23. Unbalanced forces however…. Gravity buoyancy … will make an object change speed, shape or direction.

24. The Stages of a Parachute Jump 2. Freefall 3. Deployment 4. Descent There are different forces acting at each stage. Try to work them out before going to the next slide. 1. Exit

25. Exit The force pulling the man down is his weight. At first this is far more than the upthrust (air resistance) pushing him upwards … so he accelerates downwards!

26. Freefall As he accelerates down his weight stays the same … but the upthrust (air resistance) increases rapidly. Once they are the same he stops accelerating and falls at a steady speed (terminal velocity).

27. Deployment As he opens his parachute his weight is still the same. … but the upthrust due to air resistance is suddenly huge! So he decelerates rapidly.

28. Descent Once again, his weight hasn’t changed … but as he slows the upthrust decreases until it equals his weight again. So, once again he descends at a steady (but slower) speed.

29. 3. Work Work done = Force x Distance Moved W F x D Work is actually measuring the amount of energy that has been converted from one form to another…… ….. So its units is JOULES

30. 1.5m 2kg How much work is done to lift the two bricks on to the table? Work = Force x Distance moved Force (weight) = mass x acceleration = 4kg x 10 m/s 2 = 40N 40N x 1.5m = 60J

31. 1.5m 2kg How much work is done to lift the two bricks on to the table? Work = Force x Distance moved40N x 1.5m = 60J It takes 1 joule of energy to do move a force of 1N for 1 metre So in this example the work done is 60Joules

32. 1.5m How much work is done to lift the two bricks on to the table one at a time? 2kg 2kg => 20N 20N x 1.5m = 30 JTwo bricks needing 30J of work each = 60J The work done is the same!

33. 1.5m 2kg Lifting the bricks separately means less force each time, but twice as much distance moved overall. 2kg 1.5m Some machines work this way ….. ….. Using a small force over a large distance to move a larger force over a smaller one. 60J

34. 1.5m 3m The ramp is an inclined plane. It increases the distance moved so it decreases the force needed. (small force, big movement  big force, small movement) 20N 10N

35. Levers Levers are usually used as force multipliers. A small force moving a long distance Lifts a large force a short distance

36. Here are some more force multipliers. (small force, big movement  big force, small movement)

37. ….. Alternatively levers can be distance multipliers Big force, small distance Small force, big distance

38. For instance:

39. 4. Power (Watts) Power measures how fast work is being done. P w t Power = work done time taken

40. A weightlifter lifts 350kg up 2.5 metres in 2 seconds. How much power does he use? Force (weight) = 350 kg x 10 m/s 2 = 3,500N Force = mass x accelerationWork done = force x distance Work done = 3,500 N x 2.5 m = 8,750 J Power `= work done time taken Power = 8,750 J 2 s = 4,375 W END