physics P2A

graphs
1. distance-time graphs
  1. shows the distance something has travelled and in how much time
  2. features
    1. gradient = speed
    2. flat sections = stationary
    3. straight = steady speed
    4. the steeper the graph, the faster the object is travelling
    5. downhill = going back toward starting point
    6. curves = acceleration or deceleration
    7. steepening curve = speeding up
  3. calculating speed
    1. speed = gradient
2. velocity-time graphs
  1. velocity - the speed of the object with direction specified (30mph north or 20m/s 060)
  2. features
    1. gradient = acceleration
    2. flat sections = steady speed
    3. steeper = greater acceleration or deceleration
    4. uphill = acceleration
    5. downhill = deceleration
    6. curve = changing acceleration
forces
1. weight, mass and gravity
  1. weight
    1. caused by the pull of the gravitational field
    2. mass X gravitational field strength
    3. Newtons
  2. mass
    1. just the amount of 'stuff' in an object
    2. kg
  3. gravity
    1. the force on an object implemented by the strength it is being held to the planet with
2. resultant forces
  1. the overall force on a point or object
  2. change in velocity
  3. if the resultant force on a stationary object is zero,the object will remain stationary
  4. if there is no resultant force on a moving object it'll carry on moving at the same velocity
  5. if there is a non-zero resultant force, then the object will accelerate in the direction of the force
3. when two objects interact, the forces they exert on each other are equal and opposite
4. friction
  1. always slows things down
  2. air resistance increases as speed increases
  3. objects falling through fluids reach terminal velocity
    1. fluids = air or liquid
    2. terminal velocity = maximum speed
    3. terminal velocity depends on shape and area
      1. larger area = slower velocity
      2. larger shape = slower velocity
5. a force is any external effort that causes an object to undergo a certain change, either concerning its movement or direction
6. forces change momentum
  1. when a force acts on an object, it causes a change in momentum
    1. larger force means a faster change of momentum
    2. if someone has a quick change of momentum, the forces on the body will be very large
energy
1. stopping distances
  1. sum of thinking distance and braking distance
    1. thinking distance
      1. affected by two things
        how fast you are travelling
        faster you are going, the further you will go
        how dopey you are
        tiredness
        drugs
        alcohol
        careless
    2. braking distance
      1. affected by four things
        how fast you are going
        faster you are travelling, further it takes to stop
        how good the brakes are
        better brakes, shorter distance
        how good the tyres are
        how good the grip is
        road surface
        weather
        tyres
2. work and potential energy
  1. when a force moves an object through a distance, the energy transferred and work is done
  2. work done = force X distance
  3. gravitational potential energy = mass X gravitational field strength X height
3. Joules (J)
4. kinetic energy = 1/2 X mass X speed^2
5. kinetic energy transferred = work done by brakes
6. kinetic energy gained = potential energy lost
7. work done = power X time
8. momentum = mass X velocity
car design
1. brakes
  1. the brakes reduce the kinetic energy
    1. transferring it into heat and sound energy
  2. regenerative braking systems
    1. 1) use the system that drives the vehicle to do the majority of the braking
    2. 2) rather than converting the kinetic energy into heat energy, the brakes put the vehicle in reverse. with the motor running backwards, the wheels slow
    3. 3) the motor acts as a electric generator, converting kinetic energy into electrical that is strored in the vehicle's battery.
    4. 4) this means that energy from braking is not wasted
2. safety
  1. crumple zones
    1. at front and back of the car crumple up on impact
    2. the car's kinetic energy is converted into other forms of energy by the car body as it changes shape
      1. e.g. heat energy
  2. side impact bars
    1. strong metal tubes fitted into car door panels.
    2. help direct kinetic energy of the crash away from passengers to other areas of the car
      1. e.g. the crumple zones
  3. seat belts
    1. stretch slightly, increasing the time taken for the wearer to stop
    2. reduces the forces acting on the chest
      1. some of the kinetic energy of the wearer is absorbed by the seat belt stretching
  4. air bags
    1. slow you down more gradually
    2. stop you from hitting the hard surfaces
3. power ratings
  1. the size and design of car engines determine how powerful they are
  2. the more powerful the engine it transfers from its fuel every second, and so the faster its op speed can be
  3. aerodynamic
    1. less air resistance
    2. air flows very easily and smoothly past the car
    3. can travels at higher speeds

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