P9 - Motion

• Speed


  How fast an object is moving, measured in distance per unit of time

  
• Velocity


  Speed in a given direction
• Two moving objects can have the same speed but different velocities
• An object moving round in a circle has a direction of motion that changes continuously as it goes round, so its velocity is not constant even if its speed is constant

  
• An object that travels at constant velocity travels at a constant speed without changing its direction, so it travels in a straight line in a given direction

  
• Displacement


  The distance travelled in a given direction
• Acceleration


  The change of velocity per second
• Any object with a changing velocity is accelerating
• Deceleration


  Negative acceleration, when an object slows down
• Calculating acceleration


  Change in velocity / Time taken for the change
• Initial velocity u, final velocity v, time t


  Acceleration a = (v-u)/t

  
• Deceleration is the change of velocity per second when an object slows down