Motion

• Speed is defined as the rate of change of distance.

  Equation used is: speed = distance / time

  SI units are ms^-1
• Displacement of an object is the distance it has travelled in a given direction, so it is a vector with both magnitude and direction.
• Velocity of an object is defined as the rate of change of displacement, or speed in a given direction, making velocity a vector.

  Equation used is: velocity = change in displacement / time

  SI units are ms^-1
• Acceleration is defined as the rate of change of velocity, making it a vector.

  Equation used is: acceleration = change in velocity / time

  SI units are ms^-2
• Area under a velocity time graph represents displacement
• Area under a acceleration time graph represents velocity
• Terminal Velocity of an object using light gates.

  • Set up the light gates vertically and measure the distance between them.
  • Connect them to a data logger and then release an object from rest above them, measuring the time it takes for the object to travel between the two gates.
  • Using the time and the distance, calculate the velocity.
• Acceleration of 'g' is the acceleration of an object in response to gravity.

  g = 9.81 ms^-2
• Experiment in which one can determine 'g' using an electromagnet.

  • An electromagnet holds a steel ball suspended a measured distance above a surface, then start the timer when the electromagnet is deactivated, and stop it when the surface is hit.
  • As the ball was initially resting, u = 0
  • The distance and time are known so, SUVAT can be used.
  • Calculate 'a'
• If an object is projected the horizontal velocity remains the same as there is no acceleration in the horizontal direction.
• In projectile motion the acceleration in the vertical direction is equal to the 'g' which is 9.81 ms^-2
• Instantaneous speed is the speed of an object over a very short period of time.
• Gradient of a displacement time graph is the velocity of the object
• Gradient of a velocity time graph is the acceleration of the object
• Area beneath a velocity time graph is the displacement of the object
• Thinking distance is the distance travelled by the vehicle in the time it takes the driver to react.
• Braking distance is the distance travelled by the vehicle in the time the brakes act.
• Equation for thinking distance:

  Thinking distance = reaction time of driver x speed of the car
• Factors that affect thinking distance:

  • Speed
  • Tiredness
  • Alcohol and drugs
  • Distractions
  • Age
• Factors that affect braking distance:

  • Speed
  • Road condition
  • Condition of the brakes
  • Condition of the tires
  • Mass of the car