Physics 2A Forces and their effects

acceleration and velocity time garphs
1. gradient=acceleration
2. flat sections = steady speed
3. steeper the graph
  1. greater acceleration/ decleration
4. uphill (/) accelecration
  1. downhill (\) deceleration
5. area under graph =distance in that time
6. curve = change acceleration
7. acceleration=
  1. gradient=
    1. vertical change / horizontal change
weight mass and gravity
1. force of attraction
  1. only notice when one force is big
  2. gives everything weight
  3. without it acceleration would be same throughout universe.
2. mass = stuff in object
  1. mass is the same anywhere in universe
    1. volume
3. caused by gravity
  1. weight is a force
4. weight = mass x gravitational field strength
resultant forces
1. overall force on object
  1. most times 2 forces acting on one object
  2. overall effect
    1. decides the motion
      1. acceleration
      2. decelration
      3. stop
      4. constant speed
2. means change in velocity
3. object stationary
  1. resultant force = 0N
    1. object remain stationary
4. moving object 0N
  1. keep moving at same speed/velocity
5. resultant force = more than 0N
  1. object accelerate in direction of force
    1. force = mass x acclecration
reaction forces are equal and oppostie
1. two objects interact forces exert are equal and oppostie
kinetic energy
1. movement energy
  1. anything that moves has kinetic energy
    1. kinetic energy = 1/2 x mass x speed(squared)
      1. Ek = 1/2 x m x v(squared)
2. kinetic energy depends on mass and speed
  1. big mass and fast speed = more energy
3. kinetic energy transferred is work done
  1. kinetic energy transferred = work done by brakes
    1. 1/2 x m x v (squared) = f x d
potential energy
1. gravitational potential energy
  1. due to height
    1. gravitational potential energy = mass x gravity x height
      1. Ep = m x g x h
2. falling objects convert potential into kinetic
  1. kinetic energy gained = potential energy lost
  2. some kinetic energy is transferred into heat and sound
3. elastic objects store energy as elastic potential energy
  1. any object that can return to its original shape after force is removed is elastic
    1. work is done to an elastic object to change its shape
      1. this energy is not lost but stored
        elastic potential energy
        the elastic potential energy is converted into kinetic energy when the force is removed the object returns to its original shape
  2. extension of an elastic object is directly proportional to force
    1. F = k x e
      1. f = force applied
      2. k = spring constant (depends on the material of the spring)
      3. e = extentsion
    2. there's a limit to the amount of force applied for the extension to increase proportionally
      1. limit of proportionality
        if you increase an object past this point it will remain permanently stretched
power
1. rate of doing work
  1. power = work done (energy transferred) / time taken
    1. P = E / t
2. power is measured in watts
  1. one watt = 1 joule of energy transferred per second
momentum and collisions
1. momentum (kg m/s) = mass (kg) x velocity (m/s)
  1. p = m x v
2. momentum is a property of moving objects
  1. greater mass and greater it velocity the more momentum an object has
  2. momentum before = momentum after
    1. conservation of momentum
      1. collision or explosion
car design and safety
1. forces cause change in momentum
  1. large force = faster change in momentum (greater acceleration)
    1. car crash
      1. if someone's momentum changes quick the forces on the body will be large and cause injury
      2. cars designed to safely convert kinetic energy
        in a crash there's a big change in momentum over a short time
        this means inside the car huge forces could be fatal
        this is often by increasing the time over which momentum changes lessens the forces
2. crumple zones
  1. front and back of the car crumple on impact
    1. cars kinetic energy is converted into other forms when the car body changes shape
      1. increase impact time decrease force by change in momentum
3. seat belts
  1. stretch slightly
    1. increasing the time
      1. reducing force on the chest
4. air bags
  1. gradually slow you down
    1. prevent you from hitting hard surfaces in the car

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Physics 2A Forces and their effects

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