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OCR Gateway Additional Science

P3: Forces for Transport. OCR Gateway Additional Science. W Richards. P3a Speed. Distance, Speed and Time. 07/01/2020. 07/01/2020. Speed = distance (in metres) time (in seconds). D. S. T. Freddie walks 200 metres in 40 seconds. What is his speed?

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OCR Gateway Additional Science

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  1. P3: Forces for Transport OCR Gateway Additional Science W Richards

  2. P3a Speed

  3. Distance, Speed and Time 07/01/2020 07/01/2020 Speed = distance (in metres) time (in seconds) D S T • Freddie walks 200 metres in 40 seconds. What is his speed? • Hayley covers 2km in 1,000 seconds. What is her speed? • How long would it take Lauren to run 100 metres if she runs at 10m/s? • Jake travels at 50m/s for 20s. How far does he go? • Izzy drives her car at 85mph (about 40m/s). How long does it take her to drive 20km? 5m/s 2m/s 10s 1000m 500s

  4. Distance, Speed and Time 07/01/2020 07/01/2020 Speed = distance (in metres) time (in seconds) D S T • Sarah walks 2000m in 50 minutes. What is her speed in m/s? • Jack tries to walk the same distance at a speed of 5m/s. How long does he take? • James drives at 60mph (about 100km/h) for 3 hours. How far has he gone? • The speed of sound in air is 330m/s. Molly shouts at a mountain and hears the echo 3 seconds later. How far away is the mountain? (Careful!) 0.67m/s 400s 300km 495m

  5. How speed cameras work After 1.5s After 0s Speed cameras work by recording the position of the car at a certain time apart. What is the speed of the trolley in the lab example done below?

  6. Average Speed u + v s = t 2 It is common to see “average speed cameras” near roadworks. They work by recording how long you take to cover a certain distance and then working out your average speed. • Two cameras are 1km apart and a car takes 50s to travel between them. What was the car’s average speed? • A car accelerates from 10 to 20m/s for 50s. How far has it gone? • How long would it take to travel 10km if you started at a speed of 30m/s and ended up at 50m/s after the 10km? 20m/s 750m 250s

  7. Distance-time graphs 2) Horizontal line = 4) Diagonal line downwards = • Diagonal line = 3) Steeper diagonal line = 40 30 20 10 0 Distance (metres) Time/s 20 40 60 80 100

  8. 40 30 20 10 0 Distance (metres) Time/s 20 40 60 80 100 • What is the speed during the first 20 seconds? • How far is the object from the start after 60 seconds? • What is the speed during the last 40 seconds? • When was the object travelling the fastest?

  9. 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

  10. 40 30 20 10 0 07/01/2020 07/01/2020 Distance (metres) Time/s 20 40 60 80 100 1.5m/s • What was the velocity in the first 20 seconds? • What was the velocity between 20 and 40 seconds? • When was this person travelling the fastest? • What was the average speed for the first 40 seconds? 0.5m/s 80-100s 1m/s

  11. P3b Changing Speed

  12. Acceleration 07/01/2020 07/01/2020 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? 2m/s2 120m/s 5s 2000m/s2

  13. Speed-time graphs 1) Upwards line = 4) Downward line = 2) Horizontal line = 3) Upwards line = 80 60 40 20 0 Velocity m/s T/s 10 20 30 40 50

  14. 80 60 40 20 0 07/01/2020 07/01/2020 Velocity m/s T/s 10 20 30 40 50 • 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? 40m/s 2m/s2 3m/s2 1700m

  15. 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

  16. 80 60 40 20 0 07/01/2020 07/01/2020 Velocity m/s T/s 10 20 30 40 50 • How fast was the object going after 10 seconds? • What is the acceleration from 20 to 30 seconds? • What was the deceleration from 40 to 50s? • How far did the object travel altogether? 10m/s 4m/s2 6m/s2 1500m

  17. 80 60 40 20 0 07/01/2020 07/01/2020 Velocity m/s T/s 10 20 30 40 50 This velocity-time graph shows Coryn’s journey to school. How far away does she live? 2500m

  18. Speed vs. Velocity 07/01/2020 07/01/2020 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”…

  19. Circular Motion 07/01/2020 07/01/2020 1) Is this car travelling at constant speed? 2) Is this car travelling at constant velocity?

  20. P3c Forces and Motion

  21. Force and acceleration 07/01/2020 07/01/2020 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)

  22. Force, mass and acceleration 07/01/2020 07/01/2020 F M A • 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. How heavy is the car? • A car accelerates at a rate of 5m/s2. If it weighs 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? 2m/s2 2000kg 2500N 0.5m/s2

  23. Stopping a car… 07/01/2020 07/01/2020 What two things must the driver of the car do in order to stop in time?

  24. Stopping a car… 07/01/2020 07/01/2020 Thinking distance (reaction time) Braking distance Tiredness Too much alcohol Too many drugs Poor visibility Wet roads Icy roads Tyres/brakes worn out Driving too fast Total Stopping Distance = Thinking Distance + Braking Distance

  25. Stopping Distances This diagram (taken from drivingtestsuccess.com) shows the thinking and braking distances for different speeds. What patterns do you notice? Thinking distance increases linearly Braking distance increases in a squared relationship

  26. P3d Work and Power

  27. Weight vs. Mass 07/01/2020 07/01/2020 W M g Earth’s Gravitational Field Strength is 10N/kg. In other words, a 1kg mass is pulled downwards by a force of 10N. Weight = Mass x Gravitational Field Strength (in N) (in kg) (in N/kg) 20N • What is the weight on Earth of a book with mass 2kg? • What is the weight on Earth of an apple with mass 100g? • James weighs 700N on the Earth. What is his mass? • On the moon the gravitational field strength is 1.6N/kg. What will James weigh if he stands on the moon? 1N 70kg 112N

  28. Work done 07/01/2020 07/01/2020 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

  29. Example questions 07/01/2020 07/01/2020 • Jessie pushes a book 5m along the table with a force of 5N. She gets tired and decides to call it a day. How much work did she do? • Hayley lifts a laptop 2m into the air with a force of 10N. How much work does she do? What type of energy did the laptop gain? • James does 200J of work by pushing a wheelbarrow with a force of 50N. How far did he push it? What type of energy did the wheelbarrow gain? • Jack cuddles his cat and lifts it 1.5m in the air. If he did 75J of work how much force did he use? • Freddie drives his car 1000m. If the engine was producing a driving force of 2000N how much work did the car do? 25J 20J, GPE 4m, KE 50N 2MJ

  30. A Practical Example of Doing Work 07/01/2020 Consider a rocket re-entering the Earth’s atmosphere: The rocket would initially have a very high _______ energy. This energy would then _____ due to friction caused by collisions with _______ in the atmosphere. These collisions would cause the rocket to ____ up (_____ is “being done” on the rocket). To help deal with this, rockets have special materials that are designed to lose heat quickly. Words – work, kinetic, particles, heat, decrease

  31. Energy and Power 07/01/2020 E P T The POWER RATING of an appliance is simply how much energy it uses every second. In other words, 1 Watt = 1 Joule per second E = Energy (in joules) P = Power (in watts) T = Time (in seconds)

  32. Some example questions 07/01/2020 • 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? • Tanner runs up the stairs in 5 seconds. If he transfers 1,000,000J of energy in this time what is his power rating? • How much energy does a 150W light bulb transfer in a) one second, b) one minute? • Pierre’s brain needs energy supplied to it at a rate of 40W. How much energy does it need during a 50 minute physics lesson? • Levi’s brain, being more intelligent, only needs energy at a rate of about 20W. How much energy would his brain use in a normal day? 60W 2KW 0.2MW 150J, 9KJ 120KJ 1.73MJ

  33. An example with cars Citroen Saxo, 60bhp Audi R8, 423 bhp What are the advantages and disadvantages of each car?

  34. Power 07/01/2020 W P = W t W = FxD Also, using our “work done” equation: P t P = W = FxD t t P = Fv …therefore Power (in watts) is “the rate of doing work”:

  35. Random questions on work and power 07/01/2020 50N • Jordan pushes Tom in the direction of a cliff. If he uses a force of 40N and he moves Tom 10m in 4s calculate the work done and Jordan’s power rating. • Chris runs up some stairs and has a power rating of 600W while he does so. If he does it in 5 seconds and his weight is 750N calculate how high the stairs are. • A man pulls a block of wood and uses a force of 50N. If the distance travelled horizontally is 5m calculate the work done by the man and his power if the journey lasted 10 seconds. 400J, 100W 4m 250J, 25W

  36. P3e Energy on the Move

  37. Kinetic energy 07/01/2020 07/01/2020 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

  38. Example questions 07/01/2020 07/01/2020 • Shannon drives her car at a speed of 30m/s. If the combined mass of her and the car is 1000kg what is her kinetic energy? • Issy rides her bike at a speed of 10m/s. If the combined mass of Issy and her bike is 80kg what is her kinetic energy? • Will is running and has a kinetic energy of 750J. If his mass is 60kg how fast is he running? • Josh is walking to town. If he has a kinetic energy of 150J and he’s walking at a pace of 2m/s what is his mass? 450,000J 4000J 5m/s 75kg

  39. Stopping Distances revision Recall the patterns we observed in this data: Thinking distance increases linearly Braking distance increases in a squared relationship

  40. Stopping a car… 07/01/2020 07/01/2020 What happens inside the car when it stops? In order to stop this car the brakes must “do work”. This work is used to reduce the kinetic energy of the vehicle and the brakes will warm up – this is why the braking distance depends on speed2

  41. An example question… 07/01/2020 07/01/2020 This car can apply a maximum braking force of 10,000N. If the car’s mass is 1000Kg how far is its stopping distance when it is travelling at a speed of 15m/s (roughly 30mph) and 30m/s (roughly 60mph)? 15m/s = 11.25m stopping distance 30m/s = 45m stopping distance (4 times greater)

  42. Different ways of fuelling cars What are the advantages and disadvantages of each of the following fuels?

  43. Fuel consumption Having an aerodynamic shape Having a roof box Having a “deflector” Having a window open How do the following features help or hinder fuel economy?

  44. P3f Crumple Zones

  45. Momentum 07/01/2020 07/01/2020 Momentum = Mass x Velocity P (in kgm/s)(in kg)(in m/s) M V Any object that has both mass and velocity has MOMENTUM. Momentum (symbol “p”) is simply given by the formula: What is the momentum of the following? • A 1kg football travelling at 10m/s • A 1000kg Ford Capri travelling at 30m/s • A 20g pen being thrown across the room at 5m/s • A 70kg bungi-jumper falling at 40m/s 10kgm/s 30,000kgm/s 0.1kgm/s 2800kgm/s

  46. Force and momentum mv Force = Change in momentum (in kgm/s) (in N) Time (in s) F T Also called “impulse” Newton’s second law of motion says that the force acting on an object is that object’s rate of change of momentum. In other words… For example, Rooney takes a free kick by kicking a stationary football with a force of 40N. If the ball has a mass of 0.5kg and his foot is in contact with the ball for 0.1s calculate: • The change in momentum of the ball (its impulse), • The speed the ball moves away with

  47. Example questions 07/01/2020 • Paddy likes playing golf. He strikes a golf ball with a force of 80N. If the ball has a mass of 200g and the club is in contact with it for 0.2s calculate a) the change in momentum of the golf ball, b) its speed. • Courtney thinks it’s funny to hit tennis balls at Kit. She strikes a serve with a force of 30N. If the ball has a mass of 250g and the racket is in contact with it for 0.15s calculate the ball’s change in momentum and its speed. • Tom takes a dropkick by kicking a 0.4kg rugby ball away at 10m/s. If his foot was in contact with the ball for 0.1 seconds calculate the force he applied to the ball. • Jenny strikes a 200g golf ball away at 50m/s. If she applied a force of 50N calculate how long her club was in contact with the ball for. 16Kgm/s, 80m/s 4.5Kgm/s, 18m/s 40N 0.2s

  48. Safety features 07/01/2020 07/01/2020 mv F T How do air bags and crumple zones work? Basically: • The change in momentum is the same with or without an airbag • But having an airbag increases the time of the collision • Therefore the force is reduced

  49. Car Safety Features These objects all help reduce injury by basically absorbing energy. Cars also have ABS brakes which prevent them from skidding by automatically pumping off and on to avoid the brakes locking.

  50. P3g Falling Safely

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