P3: Forces for Transport

P3: Forces for Transport

1. P3a: Speed

   • Speed = How fast an object is moving
   • To work out speed, you must know
     • Distance travelled
     • Time Taken
   • Speed= Distance/Time
   • Average Speed= (u=v)/2
     • Distance= Average speed * Time

2. P3b: Changing Speed

   • Acceleration
     • Acceleration= Change in speed per second
       • Acceleration= Speeding up
       • Deceleration= Slowing down
     • To work out acceleration, you must know:
       • Time taken for change in speed
       • Change in speed
     • Acceleration= Change in speed/ Time taken for change
   • Relative Velocity
     • Relative Velocity = Velocity 1 - Velocity 2

3. P3c: Forces and Motion

   • Forces are pushes and pulls
   • Forces are measured in Newtons (N)
   • They can be:
     • Gravity
     • Friction
     • Air Resistance
   • Force = Mass * Acceleration
   • Stopping distance
     • Stopping Distance = Thinking Distance + Braking Distance
     • Stopping Distance Depends on:
       • Thinking distance
         • Increased if:
           • Vehicle is travelling fast
           • Driver is:
             • Ill
             • Tired
             • Under influence of Drugs
           • Driver is distracted
           • There is poor visibility
       • Braking Distance
         • 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
     • As speed of car increases:
       • Thinking distance increases linearly
       • Breaking distance increases as square of the speed:
         • eg if speed doubles, then breaking distance increases by 2 squared

4. P3d: Work and Power

   • Work is done when a force moves an object
   • Work done = Energy transferred
   • Amount of work done depends on:
     • Size of force (in newtons)
     • Distance object is moved in metres (in the direction of the force)
   • Work done = Force * Distance
   • Weight
     • Weight = Mass * Gravitational field strength
   • Fuel Consumption
     • Fuel consumption depends on
       • Engine size
       • Force required to work against friction
       • Driving style and speed
       • Road conditions
       • Tyre pressure
   • Power
     • Measure of how quickly work is done
     • Power = Work done/Time

5. P3e: Energy on the Move

   • Kinetic energy
     • Kinetic energy is energy an object has due to its movement
     • Depends on:
       • Mass of object
       • Speed of object
     • Kinectic energy = 0.5 * Mass * Speed squared
   • Fuels
     • Biodiesel = Liquid fuel made from plants
       • Although do not affect Carbon dioxide in atmosphere, transporting them usually has to use some sort of fossilfueled vehicle
     • Electricity
       • Solar power
         • Unreliable in UK as there is little sunlight
       • Batteries
     • Hydrogen fuel cells

6. P3f: Crumple Zones

   • Momentum
     • Momentum = Mass * Velocity
   • Force
     • Force = Momentum change / Time
     • Force = Mass * Acceleration
   • Car Safety features
     • To Protect Passengers
       • Crumple Zones
       • Collapsible Steering Colums
       • Airbags
       • Seat Belts
       • Safety Cage
     • To Prevent Accidents
       • Anti-Locking Brake System
         • Pump on and off when skidding
           • Increases area of tyres in contact with road
             • Gives driver better control of the car
       • Traction Control
         • No skidding during acceleration
       • Electric Windows
       • Paddle Shift Controls
         • Keep both hands on steering wheel when changing gear and adjusting radio

7. P3g: Falling Safely

   • Frictional forces reduce objects kinetic energy, acting against its movement and therefore slowing it down
     • We can stop this by:
       • Changing shape of an object
       • Adding a lubricant
     • Drag
     • Friction
     • Air resistance
   • Terminal Speed
     • Falling objects experience two forces:
       • Weight
         • Downward
         • Stays same always on earth
         • Due to pull of the Earths gravity
         • 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
       • Air Resistance/Drag
         • Upward
         • Increases the faster an object falls
         • If there is no atmosphere, there can be no air resistance/drag
         • Larger and faster objects will have larger air resistance/drag forces
         • If an objects drag force equals its driving force, then it will reach its terminal velocity
     • Gravity
       • The Earths gravitational field strength is unaffected by atmospheric changes, but can be slightly different in different places of the Earth

8. P3h: The Energy Of Games And Theme Rides

   • Gravitational Potential energy
     • Gravitational potential energy is the energy an object has due to its position on the Earths gravitational field
       • If an object can fall, it has GPE
         • A heavier object has a higher GPE than a lighter object
         • A higher up object has a higher GPE than a lower down object
       • GPE = Mass * Gravitational Field Strength * Vertical Height
     • Gravitational Field Strength is constant
   • Gravitaitonal Potential Energy and Kinetic Energy
     • When an object falls, its GPE is transferred into KE
       • See phys revsion guide for good diagram on this, pg 52
     • If mass is doubled, KE is doubled
     • If speed is doubles, KE is quadrupled
     • Increase in GFS will increase the GPE, but to do this, you would need to move to anther planet
     • mgh = 0.5 * m * v squared
     • 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