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Motion

Motion. There are four sections to this…. 1. Speed and Acceleration. 2. Forces. 3. Work. 4. Power. Click on the section you want. 1. Speed and Acceleration. D. distance. Speed =. time. S. T. D. x. S =. T. Speed. Speed tells you how fast something is travelling.

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Motion

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

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

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

  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 D = S x T S x T D = 700 x 9 D = 6,300 km

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

  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? D D T = S S x T 550 km T = 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. A. B. Distance (m) Distance (m) Distance (m) C. Time (s) Time (s) Time (s) Distance – Time Graphs Constant speed Constant speed (but slower than A) The gradient of the line is the speed. Stationary The steeper the line, the faster the speed!

  12. B. A. Acceleration Distance (m) Distance (m) Distance (m) C. Deceleration Time (s) Time (s) Time (s) Distance – Time Graphs Constant speed 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. = change change in speed (m/s) Acceleration = time (s) s m/s a x t Units = s = m/s2 = ms-2 = metres per second squared.

  15. s a x t 20 m/s a = 2s When the parachutist jumps from the plane his speed downwards goes from 0m/s to 20m/s in just 2 seconds. His change in speed is from 0m/s to 20 m/s So his acceleration is……. = 10 m/s2 (10 m/s2 is the acceleration due to gravity)

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

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

  18. 2. Forces

  19. push pull twist A Force is a:

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

  21. Reaction Action Forces always act in pairs.

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

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

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

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

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

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

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

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

  30. How much work is done to lift the two bricks on to the table? Work = Force x Distance moved 40N x 1.5m = 60J 1.5m 2kg 2kg Force (weight) = mass x acceleration = 4kg x 10 m/s2 = 40N

  31. How much work is done to lift the two bricks on to the table? Work = Force x Distance moved 40N x 1.5m = 60J 1.5m 2kg 2kg 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. 2kg 2kg 2kg => 20N 2kg => 20N How much work is done to lift the two bricks on to the table one at a time? 20N x 1.5m = 30 J Two bricks needing 30J of work each = 60J 1.5m The work done is the same!

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

  34. 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) 3m 10N 1.5m 20N

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

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

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

  38. For instance:

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

  40. Force = mass x acceleration Force (weight) = 350 kg x 10 m/s2 = 3,500N Work done = force x distance Work done = 3,500 N x 2.5 m = 8,750 J work done Power `= time taken 8,750 J = 4,375 W Power = 2 s A weightlifter lifts 350kg up 2.5 metres in 2 seconds. How much power does he use? END

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