P3: Forces for Transport

P3a: Speed
1. Speed = How fast an object is moving
2. To work out speed, you must know
  1. Distance travelled
  2. Time Taken
3. Speed= Distance/Time
4. Average Speed= (u=v)/2
  1. Distance= Average speed * Time
P3b: Changing Speed
1. Acceleration
  1. Acceleration= Change in speed per second
    1. Acceleration= Speeding up
    2. Deceleration= Slowing down
  2. To work out acceleration, you must know:
    1. Time taken for change in speed
    2. Change in speed
  3. Acceleration= Change in speed/ Time taken for change
2. Relative Velocity
  1. Relative Velocity = Velocity 1 - Velocity 2
P3c: Forces and Motion
1. Forces are pushes and pulls
2. Forces are measured in Newtons (N)
3. They can be:
  1. Gravity
  2. Friction
  3. Air Resistance
4. Force = Mass * Acceleration
5. Stopping distance
  1. Stopping Distance = Thinking Distance + Braking Distance
  2. Stopping Distance Depends on:
    1. Thinking distance
      1. Increased if:
        Vehicle is travelling fast
        Driver is:
        Ill
        Tired
        Under influence of Drugs
        Driver is distracted
        There is poor visibility
    2. Braking Distance
      1. Increased if:
        Vehicle is travelling fast
        Poor weather or road conditions
        Wet
        Icy
        Friction between tyres and road decreased
        Mass of vehicle increased
        Breaking force applied is decreased
  3. As speed of car increases:
    1. Thinking distance increases linearly
    2. Breaking distance increases as square of the speed:
      1. eg if speed doubles, then breaking distance increases by 2 squared
P3d: Work and Power
1. Work is done when a force moves an object
2. Work done = Energy transferred
3. Amount of work done depends on:
  1. Size of force (in newtons)
  2. Distance object is moved in metres (in the direction of the force)
4. Work done = Force * Distance
5. Weight
  1. Weight = Mass * Gravitational field strength
6. Fuel Consumption
  1. Fuel consumption depends on
    1. Engine size
    2. Force required to work against friction
    3. Driving style and speed
    4. Road conditions
    5. Tyre pressure
7. Power
  1. Measure of how quickly work is done
  2. Power = Work done/Time
P3e: Energy on the Move
1. Kinetic energy
  1. Kinetic energy is energy an object has due to its movement
  2. Depends on:
    1. Mass of object
    2. Speed of object
  3. Kinectic energy = 0.5 * Mass * Speed squared
2. Fuels
  1. Biodiesel = Liquid fuel made from plants
    1. Although do not affect Carbon dioxide in atmosphere, transporting them usually has to use some sort of fossilfueled vehicle
  2. Electricity
    1. Solar power
      1. Unreliable in UK as there is little sunlight
    2. Batteries
  3. Hydrogen fuel cells
P3f: Crumple Zones
1. Momentum
  1. Momentum = Mass * Velocity
2. Force
  1. Force = Momentum change / Time
  2. Force = Mass * Acceleration
3. Car Safety features
  1. To Protect Passengers
    1. Crumple Zones
    2. Collapsible Steering Colums
    3. Airbags
    4. Seat Belts
    5. Safety Cage
  2. To Prevent Accidents
    1. Anti-Locking Brake System
      1. Pump on and off when skidding
        Increases area of tyres in contact with road
        Gives driver better control of the car
    2. Traction Control
      1. No skidding during acceleration
    3. Electric Windows
    4. Paddle Shift Controls
      1. Keep both hands on steering wheel when changing gear and adjusting radio
P3g: Falling Safely
1. Frictional forces reduce objects kinetic energy, acting against its movement and therefore slowing it down
  1. We can stop this by:
    1. Changing shape of an object
    2. Adding a lubricant
  2. Drag
  3. Friction
  4. Air resistance
2. Terminal Speed
  1. Falling objects experience two forces:
    1. Weight
      1. Downward
      2. Stays same always on earth
      3. Due to pull of the Earths gravity
      4. Objects fall due to weight
        Weight is a force pulling towards the centre of the planet
        Strength of this force depends on the gravity of the planet
    2. Air Resistance/Drag
      1. Upward
      2. Increases the faster an object falls
      3. If there is no atmosphere, there can be no air resistance/drag
      4. Larger and faster objects will have larger air resistance/drag forces
      5. If an objects drag force equals its driving force, then it will reach its terminal velocity
  2. Gravity
    1. The Earths gravitational field strength is unaffected by atmospheric changes, but can be slightly different in different places of the Earth
P3h: The Energy Of Games And Theme Rides
1. Gravitational Potential energy
  1. Gravitational potential energy is the energy an object has due to its position on the Earths gravitational field
    1. If an object can fall, it has GPE
      1. A heavier object has a higher GPE than a lighter object
      2. A higher up object has a higher GPE than a lower down object
    2. GPE = Mass * Gravitational Field Strength * Vertical Height
  2. Gravitational Field Strength is constant
2. Gravitaitonal Potential Energy and Kinetic Energy
  1. When an object falls, its GPE is transferred into KE
    1. See phys revsion guide for good diagram on this, pg 52
  2. If mass is doubled, KE is doubled
  3. If speed is doubles, KE is quadrupled
  4. Increase in GFS will increase the GPE, but to do this, you would need to move to anther planet
  5. mgh = 0.5 * m * v squared
  6. When an object is falling at terminal speed, speed does not change, so no change in KE, however, GPE decreases as the object is still working againstfriction or air resistance

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P3: Forces for Transport

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	Created by PatrickNoonan about 12 years ago

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