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OCR Additional Science

OCR Additional Science. P3 Forces for Transport. AGAC. Speed vs. Velocity. This car is travelling at a speed of 20m/s. This car is travelling at a velocity of 20m/s east. Speed is simply how fast you are travelling…. Velocity is “speed in a given direction”…. Distance, Speed and Time.

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OCR Additional Science

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  1. OCR Additional Science P3 Forces for Transport AGAC

  2. Speed vs. Velocity This car is travelling at a speed of 20m/s This car is travelling at a velocity of 20m/s east Speed is simply how fast you are travelling… Velocity is “speed in a given direction”…

  3. Distance, Speed and Time Speed=distance (in m) time (in s) d t S (in m/s) Dave walks 20 metres in 4 seconds. What is his speed? Laura covers 12m in 3 seconds. What is her speed? How long would it take to run 100 metres if you run at 10m/s Steve travels at 50m/s for 20s. How far does he go? Susan drives her car at 40m/s. How long does it take her to drive 200m? 5 m/s 4 m/s s 10 1000 m 5 s

  4. Distance-time graphs • 2) Horizontal line = • 4) Diagonal line downwards = • Diagonal line = • 3) Steeper diagonal line = 40 30 20 10 0 Notmoving Constant speed… back to start Distance (metres) Time/s 2 4 6 8 10 Constant speed Faster constant speed

  5. 40 30 20 10 0 d s x t Distance (metres) Time/s 2 4 6 8 10 10/2= 5m/s • What is the speed during the first 2 seconds? • How far is the object from the start after 6 seconds? • What is the speed during the last 4 seconds? • When was the object travelling the fastest? 40m 40/4= 10m/s 4 to 6 seconds

  6. Distance-time graph for non-uniform motion Object is accelerating up to here Object is now decelerating 40 30 20 10 0 Distance (metres) Time/s 20 40 60 80 100

  7. Acceleration v-u Acceleration=change in velocity (in m/s) (in m/s2)time taken (in s) a t • A cyclist accelerates from 0 to 10m/s in 5 seconds. What is her acceleration? • A ball is dropped and accelerates downwards at a rate of 10m/s2 for 12 seconds. How much will the ball’s velocity increase by? • A car accelerates from 10 to 20m/s with an acceleration of 2m/s2. How long did this take? • A rocket accelerates from 1,000m/s to 5,000m/s in 2 seconds. What is its acceleration? 10/5= 2m/s2 10x12= 120m/s 10/2= 5s 4000/2= 2000m/s2

  8. Velocity-time graphs • 1) Upwards line = • 4) Downward line = • 2) Horizontal line = • 3) Upwards line = 80 60 40 20 0 constant acceleration constant deceleration Velocity m/s T/s 10 20 30 40 50 constant velocity constant acceleration

  9. 80 60 40 20 0 v a x t ½ x 10 x 20= clue: it’s the area under the graph! Velocity m/s 10 x 40= ½ x 20 x 60= ½ x 10x40 = T/s 10 x 40= 10 20 30 40 50 40m/s • How fast was the object going after 10 seconds? • What is the acceleration from 20 to 30 seconds? • What was the deceleration from 30 to 50s? • How far did the object travel altogether? 2m/s2 -3m/s2 200m + 400m + 400m + 100m + 600m = 1700m

  10. Speed-time graph for non-uniform motion Object’s acceleration is increasing Object’s acceleration is decreasing 40 30 20 10 0 Distance (metres) Time/s 20 40 60 80 100

  11. What is a force? A force is a “push” or a “pull”. Some common examples: ___ ________ (drag) – acts against anything moving through air ________ – pulls things downwards _____ – acts against anything moving ______ – keeps things afloat upthrust Air resistance friction weight Words –

  12. Balanced and unbalanced forces Reaction Consider a camel standing on a road. What forces are acting on it? These two forces would be equal – we say that they are BALANCED. The camel doesn’t move anywhere. Weight

  13. Balanced and unbalanced forces Reaction What would happen if we took the road away? Weight

  14. Balanced and unbalanced forces What would happen if we took the road away? The camel’s weight is no longer balanced by anything, so the camel falls downwards…

  15. Air Resistance Air resistance is a force that opposes motion through air. The quicker you travel, the bigger the air resistance: The bigger the arrow, the bigger the force The same applies to a body falling through a liquid (called “drag” or “upthrust”).

  16. Examples of Air Resistance

  17. Balanced and unbalanced forces 1 In each of these situations the car is not moving before each force is applied car accelerates car accelerates car does not move car accelerates

  18. Balanced and unbalanced forces 2 Stage 1 car accelerates Car starting off Stage 2… continuing from stage 1 (moving) car still accelerates but not as much as in Stage 1 Next slide for stage 3

  19. Balanced and unbalanced forces 2 Stage 3… continuing from Stage 2 (moving) Car moves at a steady speed Now see the next slide To see how this can be Put into a graph ….. Stage 4… continuing from Stage 3 (moving) Car decelerates

  20. Balanced and unbalanced forces Velocity constant speed accelerating decelerating accelerating Stage 1 Stage 2 Stage 3 Stage 4 Time

  21. Balanced and unbalanced forces 1) This animal is either ________ or moving with _____ _____… 2) This animal is getting _________… stationary faster constant speed 3) This animal is getting _______…. 4) This animal is… slower stationary

  22. Force and acceleration F M A If the forces acting on an object are unbalanced then the object will accelerate, like these wrestlers: Force (in N) = Mass (in kg) x Acceleration (in m/s2)

  23. Force, mass and acceleration F A M • A force of 1000N is applied to push a mass of 500kg. How quickly does it accelerate? • A force of 3000N acts on a car to make it accelerate by 1.5m/s2. What mass has the car? • A car accelerates at a rate of 5m/s2. If it has a mass of 500kg how much driving force is the engine applying? • A force of 10N is applied by a boy while lifting a 20kg mass. How much does it accelerate by? 1000 = 500 2m/s2 3000= 1.5 2000Kg 2500N 500 x 5 = 10 = 20 0.5 m/s2

  24. Stopping a car… Thinking distance Braking distance The following factors INCREASE distances Tiredness Too much alcohol Too many drugs Poor visibility = + Stopping distance Thinking distance Braking distance Wet roads Icy roads Tyres/brakes worn out Driving too fast

  25. Car Safety Features Seat belts Air bags Rigid cage Paddle controls Crumple zone

  26. Work Done 4 Each Worker needs to do the same amount of work in lifting these boxes on to the shelves 3 2 A B C A B C 1

  27. Work Done 4 3 Worker A lifts 4 boxes on to the 1st shelf 2 A B C A B C A A A A 1

  28. Work Done 4 3 Worker B lifts 2 boxes on to the 2nd shelf B B 2 A B C A B C A A A A 1

  29. Work Done Worker C lifts 1 box on to the 4th shelf C 4 3 B B 2 A B C A B C A A A A 1

  30. Work Done No. of boxes x height 1 x 4 = 4 C 4 “box” = weight or force “height” = distance moved 3 No. of boxes x height 2 x 2 = 4 B B 2 A B C No. of boxes x height 4 x 1 = 4 A B C A A A A 1

  31. Work done W F D When any object is moved around work will need to be done on it to get it to move (obviously). We can work out the amount of work done in moving an object using the formula: Work done=Forcexdistance moved in J in N in m

  32. Example questions • Bori pushes a book 5m along the table with a force of 5N. He gets tired and decides to call it a day. How much work did he do? • Alicia lifts a laptop 2m into the air with a force of 10N. How much work does she do? • Martin does 200J of work by pushing a wheelbarrow with a force of 50N. How far did he push it? • Chris cuddles his cat and lifts it 1.5m in the air. If he did 75J of work how much force did he use? • Carl drives his car 1000m. If the engine was producing a driving force of 2000N how much work did the car do? 25J 20J 4m 50N 2 000 000J

  33. Work and Power W P T The POWER RATING of an appliance is simply how much work it does (i.e. how much energy it transfers) every second. In other words, 1 Watt = 1 Joule per second W = Work done (in joules) P = Power (in watts) T = Time (in seconds)

  34. Some example questions • What is the power rating of a light bulb that transfers 120 joules of energy in 2 seconds? • What is the power of an electric fire that transfers 10,000J of energy in 5 seconds? • Isobel runs up the stairs in 5 seconds. If she transfers 1,000,000J of energy in this time what is his power rating? 60W 2000W 200 000W

  35. Kinetic energy Any object that moves will have kinetic energy. The amount of kinetic energy an object has can be found using the formula: Kinetic energy = ½ x mass x velocity squared in J in kg in m/s KE = ½ mv2

  36. Example questions KE =1/2mv2 • Emily drives her car at a speed of 2m/s. If the combined mass of her and the car is 1000kg what is her kinetic energy? • 2) Max rides his bike at a speed of 10m/s. If the combined mass of Max and his bike is 80kg what is his kinetic energy? KE =1/2 mv2 KE = 0.5 x 1000 x (2)2 KE = 2000 J KE =1/2 mv2 KE = 0.5 x 80 x (10)2 KE = 4000 J

  37. Terminal Velocity Consider a skydiver: • At the start of his jump the air resistance is _______ so he _______ downwards. small accelerates 2) As his speed increases his air resistance will _______ increase 3) Eventually the air resistance will be big enough to _______ the skydiver’s weight. At this point the forces are balanced so his speed becomes ________ - this is called TERMINAL VELOCITY equal constant Words – increase, small, constant, equal, accelerates

  38. Terminal Velocity Consider a skydiver: • 4) When he opens his parachute the air resistance suddenly ________, causing him to start _____ ____. increases slowing down 5) Because he is slowing down his air resistance will _______ again until it balances his _________. The skydiver has now reached a new, lower ________ _______. decrease weight terminal velocity terminal velocity, weight, decrease, increases, slowing down Words:

  39. Velocity-time graph for terminal velocity… Parachute opens – diver slows down Speed increases… Terminal velocity reached… On the Moon New, lower terminal velocity reached Diver hits the ground Velocity No air resistance ! Time

  40. Gravitational Potential Energy To work out how much gravitational potential energy (GPE) an object gains when it is lifted up we would use the simple equation… GPE = Mass xAcceleration of free-fall x Change in height (Joules) (newtons)(=10N/kg)(metres)

  41. Gravitational Potential Energy GPE On Earth g = 10N/kg. This means that every kilogram on Earth experiences a downwards weight of 10N h m g To work out how much gravitational potential energy (GPE) an object gains when it is lifted up we would use the simple equation… GPE = Mass xgravitational field strength x Change in height (Joules)(kg)(N/kg)(metres) Now let us consider an earlier problem….

  42. Work Done GPE= mxgxh C 1x10x4=40J In this example the work done produces an increase in potential energy 4 3 GPE= mxgxh B B 2x10x2 = 40J 2 GPE= mxgxh A B C 4x10x1 = 40J A A A A 1 Each box has a mass of 1Kg and the shelves are 1m apart Each worker has transferred 40J into GPE for the boxes

  43. Example questions GPE mxgxh • How much gravitational potential energy have the following objects gained?: • A brick that has a mass of 1kg and is lifted to the top of a house (10m), • A 1,000kg car lifted by a ramp up to a height of 2m, • A 70kg person lifted up 50m by a ski lift. • How much GPE have the following objects lost?: • 4. A 0.2kg football dropping out of the air after being kicked up 30m, • 5. A 50g egg falling from a nest 10m above the ground • 6. A 1,000kg car falling off its 2m ramp. 3. GPE=70x10x50= 35000J 1. GPE = 1x10x10= 100J 2. GPE=1000x10x2= 20 000J 4. 60J 5. 5J 6. 20 000J

  44. Roller Coasters 1) Electrical energy is transferred into gravitational potential energy 3) Kinetic energy is transferred back into gravitational potential energy 2) Gravitational potential energy is transferred into kinetic energy

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