P9 – Motion

• Distance


  How far an object moves, does not involve direction, scalar quantity
• Displacement

  Includes both the distance an object moves, measured in a straight line from the start point to the finish point and the direction of that straight line, vector quantity
• Speed


  Does not involve direction, scalar quantity

  The rate of change of position of an object in any direction
• The speed of a moving object is rarely constant
• Factors affecting speed of walking, running, cycling


  • Age
  • Terrain
  • Fitness
  • Distance travelled
• Typical values for speed


  • Walking ̴ 1.5 m/s
  • Running ̴ 3 m/s
  • Cycling ̴ 6 m/s
• The speed of sound and the speed of the wind also vary
• Typical value for speed of sound in air


  330 m/s
• Calculating distance travelled at constant speed

  distance travelled = speed × time
• Speed

  Scalar quantity
• Velocity

  Vector quantity, can only be constant if direction is constant
• In circular motion, the direction is continuously changing
• Calculating speed from a distance-time graph


  Speed is equal to the gradient of the graph
• Calculating acceleration

  acceleration = change in velocity divided by time taken
• Deceleration

  An object that slows down
• Calculating acceleration from a velocity-time graph


  The acceleration of an object can be calculated from the gradient of a velocity–time graph
• Calculating distance travelled from a velocity-time graph

  The distance travelled by an object (or displacement of an object) can be calculated from the area under a velocity–time graph
• Calculating final velocity from initial velocity, acceleration and distance

  final velocity^2 = 2 × acceleration × distance