Speed

• Measuring Speed

  • Speed is the distance travelled by an object every second
  • The simplest way to measure the speed of an object, is to time how long it takes to travel a known distance and use the equation:

  A) Speed

  B) Distance

  C) Time

  
• To compare the average falling speed of a tennis ball to a plastic cone, for example, you could use:

  • A metre rule to measure the distance they fall from
  • A timer to measure how long they take to reach the ground
  • It would not be practical to use a metre rule to measure the length of an athletics track though
  • In this instance, a more appropriate piece of equipment would be a (long!) tape measure, or even better, a trundle wheel
• Using Lights Gates to Measure Time

  • Light gates are digital equipment that allow times to be measured accurately
  • A light gate can be used to start a timer when an object passes through it and stops as the object passes through it

  Single Light Gates to Measure Speed

  • A single light gate can also be used to measure the speed of an object as it passes through
  • The distance travelled is given by the length of the flag passing through the light gate. This is timed
  • The two measurements for distance travelled and time taken can then be used in the equation for speed
• Calculating Speed

  • For objects that are moving with a constant speed, use the equation below to calculate the speed:

  v= s / t

  • Where:
  • v = speed in metres per second (m/s)
  • s = distance travelled in metres (m)
  • t = time taken in seconds (s)
• Calculating Average Speed

  • In some cases, the speed of a moving object is not constant
  • For example, the object might be moving faster or slower at certain moments in time (accelerating and decelerating)
  • Because its speed is not constant, it is moving with non-uniform motion
  • The average speed of an object is given by the equation:
  • Total distance is again measured in metres, m
  • Total time is measured in seconds, s
  • Average speed is therefore also measured in metres per second, m/s
• Average Speed & Non-Uniform Motion

  • The average speed of an object is rarely constant
  • Hikers change their pace continuously as they walk
  • Bumblebees buzz around in all directions with varying speed
  • Cars are constantly speeding up and slowing down throughout a journey
  • Non-uniform motion refers to motion that is changing
  • Changing motion can mean the object is changing its speed, direction or both