Motion and Safety

Cards (17)

  • What is the resultant force that acts on an object moving in a circle called, and in which direction does it act?
    The centripetal force, it acts towards the centre of the circle.
  • What is inertial mass?
    A measure of how difficult it is to change a given object’s velocity. The ratio of force over acceleration.
  • Newton’s third law
    Whenever two objects interact, the forces that they exert on eachother are equal and opposite.
  • Equation to calculate an object‘s momentum.
    Momentum = Mass x Velocity
  • Units for momentum
    kgm/s (kilogram metres per second)
  • In a closed system, what can be said about the momentum before and after a collision?
    The total momentum before and after are equal.
  • Change in momentum =
    Force x Time
  • How can you measure human reaction times?
    Using the ruler drop test, person A and person B hold each end of a ruler with the 0cm mark at the bottom, person A drops the ruler without telling person B, person B catches it, the distance travelled corresponds to their reaction time.
  • Why is it important that the 0cm mark is at the bottom?
    So you can obtain the distance directly without having to calculate it; otherwise, a zero error would need to be accounted for.
  • What is the stopping distance equal of a vehicle equal to?
    The sum of thinking distance and braking distance
  • For a given braking distance, if the vehicle’s speed is increased, what can be said about its stopping distance?
    The stopping distance is increased with an increase in speed.
  • Give a typical range of values for human reaction time
    0.2 - 0.9 seconds
  • Factors which can affect a driver’s reaction time.
    Tiredness, drugs, alcohol
  • Factors affecting breaking distance
    Adverse road conditions, poor tyre/brake conditions
  • Energy transfers when a car applies its brakes
    Work is done by the friction force between the breaks and the wheel, kinetic energy of the wheel is converted to heat and is disappeared to the surrounds through the brake discs
  • To stop a car in a given distance, if its velocity is increased, what must happen?
    The braking force must also be increased
  • Consequences of a vehicle undergoing very large decelerations
    Kinetic energy converted to heat is very high, causing brakes to overheat, loss of control of the vehicle