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Physics 2

Interaction between objects. GCSE Additional Science. Chapter 15. Physics 2. Forces working in Pairs.

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Physics 2

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  1. Interaction between objects GCSE Additional Science Chapter 15 Physics 2

  2. Forces working in Pairs It doesn’t matter what direction you place the force on the trolley, the trolley will place a force of the same magnitude, but in the opposite direction. The forces don’t cancel each other out, as the two forces act on different bodies. Force ‘A’ that you exert on the trolley. Force ‘B’ exerted by the trolley (on you) – it is equal and opposite to force ‘A’. Force A Force B Constant speed GCSE Additional Science Chapter 15

  3. Work Done Force (N) W F × d Distance Force moved (m) As an object is moved, you do WORK and you have to use energy. To calculate the work done, you must use: GCSE Additional Science Chapter 15 Work (J) = Force (N) x Distance Force moved (m)

  4. Example Questions • Sion pushes a block 5m across a table with a force of 5N. He tires and stops. How much work did Sion do? • Anna lifts her school bag 2m up in the air with a force of 10N. How many times did she do it? • Mathew does 200J worth of work whilst pushing a box with the force of 50N. What distance did he move the box? • Cai lifts his cat 1.5m into the air. If he had done 75J worth of work, how much force did he use? • Carl drives a car over 1000m. If the engine exerts a force of 2000N, how much work is done by the car? GCSE Additional Science Chapter 15 ANSWERS

  5. Kinetic Energy Higher Every moving body has Kinetic Energy. It is possible to calculate a moving body’s kinetic energy by using: Kinetic Energy = mass (kg) x speed squared (m/s)2 2 Kinetic Energy =m x v2 2 GCSE Additional Science Chapter 15 For a diver weighing 70kg travelling at 54m/s……… Kinetic Energy = ½ × 70 × 542 = 102,060J = 102kJ

  6. Exemplar Questions • Megan drives her car at a speed of 30m/s. If the total mass is 1000kg what is her kinetic energy? • Sioned’s speed on her bike is 10m/s. The total mass of Sioned and her bike is 80kg, so what is her kinetic energy? • Dan runs with a kinetic energy of 750J. His mass is 60kg; what’s his speed? • Geraint walks to school. His kinetic energy is 150J and his speed is 2m/s, so what is his mass? GCSE Additional Science Chapter 15 ANSWERS

  7. Potential Energy HIGHER Potential energy is the energy that every object has due to its position. It is possible to calculate an object’s potential energy by using: Potential Energy = mass x gravitational strength x height (J) (kg) (m/s2) (m) Potential Energy = mgh GCSE Additional Science Chapter 15 For the book on top of the pile, it has a mass of 0.7kg and it’s 2m from the floor, so ……… Potential energy = 0.7 × 10 × 2 = 14J

  8. Friction • What is friction? • Give 3 examples where friction can be a problem. • Give 3 examples where friction can be useful. • What effect does friction have on surfaces? GCSE Additional Science Chapter 15

  9. Braking Distances for a car… • A car’s braking distance is composed of two elements: • The thinking distance – this is the distance you travel whilst reacting. • Braking distance – this is the distance travelled whilst braking. Thinking distance Braking distance Total 14m 9m 23m 13m/s (30 m.p.h.) 38m 15m 53m 22m/s (50 m.p.h.) 21m 75m 31m/s (70 m.p.h.) 96m GCSE Additional Science Chapter 15 You do not need to learn the above figures for the exam, but they show how the car’s speed affect its stopping distance. What else affects a car’s stopping distance?

  10. A Car’s Stopping Distance … Thinking distance Braking distance High speed Tiredness Alcohol Drugs Impaired vision Ice on the road Wet road surface Chapter 15 GCSE Additional Science Worn tyres or brakes High speed

  11. Car’s Stopping Distance Visit the website below to see video clips on the effects of speed, tiredness, alcohol misuse etc. on the stopping distance. http://www.thinkroadsafety.gov.uk/mediacentre/mediapage.htm GCSE Additional Science Chapter 15

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