motion

• Speed


  The rate of change of distance
• Instantaneous speed


  The speed of an object over a very short time interval
• Displacement


  The distance an object has travelled in a given direction

  
• Velocity


  The rate of change of displacement

  
• Acceleration


  The rate of change of velocity
• Acceleration


  • An object is accelerating when its speed is increasing
  • An object is decelerating when its speed decreases
  • An object will also accelerate when its direction of travel changes, such as in circular motion
• Displacement-time graph


  • Flat line = stationary object
  • Line with constant gradient = constant velocity
  • Curved line = accelerating or decelerating

  
• Velocity-time graph


  • Flat line = constant velocity
  • Line with constant gradient = constant acceleration
  • Curve = changing acceleration
  • Area under graph = displacement

  
• These equations can be used in both horizontal and vertical motion
• In vertical motion, the maximum height is reached when the velocity = 0, and acceleration vertically is usually due to gravity
• If the acceleration of the object changes to another constant value, then the motion during this time must be calculated separately from the period of initial acceleration

  
• Determining terminal velocity


  1. Use light gates connected to a timer or data logger

  2. Record time when each of two light beams are broken by the object

  3. Use known distance between light-gates to calculate velocity
• The acceleration of free fall, g, is 9.81 ms-2
• Determining acceleration of free fall, g

  1. Use trapdoor and electromagnet

  2. Film fall of small metal ball against ruler
• Projectile motion


  An object that is thrown at an angle to the horizontal, and therefore moves in both the horizontal and vertical planes
• Stopping distance


  The total distance travelled from when the driver of the car sees a hazard requiring them to stop, to the point they actually stop
• Thinking distance


  The distance travelled between the moment the hazard is spotted, and the moment the driver applies the brake
• Braking distance


  The distance travelled from the time the brake is applied to the time the vehicle comes to a complete stop
• Factors affecting stopping distance

  • Initial speed of car
  • Driver's reaction time (affected by tiredness, alcohol/drugs, distractions)
  • Road conditions (e.g. icy, wet)
  • Car conditions (e.g. bald tyres, poor brakes, heavy load)