force and motion

• Speed is how quickly an object travels a certain distance
• Common units for speed are metres per second (m/s), kilometres per hour (km/h) and miles per hour (mph)
• The average speed is calculated from the total distance travelled and the total time taken
• Instantaneous speed is the speed at a particular point in a journey
• Speed can be calculated using the equation: (average) speed (m/s) = distance (m) / time taken (s)
• The distance travelled can be calculated from speed and time: distance travelled = average speed × time (m/s) (s)
• To measure speed in the laboratory, measure distance and time. For fast-moving objects, using light gates is more accurate than using a stopwatch
• A journey can be represented on a distance-time graph
• On a distance-time graph:

  • Horizontal lines mean the object is stationary
  • Straight, sloping lines mean the object is travelling at a constant speed
  • The steeper the line, the faster the object is travelling
  • Speed is calculated from the gradient of the line