Calculating Speed (OCR Gateway GCSE Physics)

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

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

• 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

A hiker might have an average speed of 2.0 m/s, whereas a particularly excited bumble bee can have average speeds of up to 4.5 m/s

• The equation for average speed can be rearranged with the help of a formula triangle as shown:

Average speed, total distance, time formula triangle

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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

Race drivers know all about non-uniform motion, especially slowing down for corners and speeding up on the straight sections of track

Step 1: List the known quantities

• • Distance, s = 100 m
  • Time, t = 10.49 s

Step 2: Write the relevant equation

• • Sprinters typically speed up out of the blocks up to some maximum speed
  • Because Florence’s speed changes over the race, we can calculate her average speed using the equation:

average speed = total distance ÷ time taken

Step 3: Check any unit conversions

• • Check that all quantities given in the question are in standard units
  • In this example, they are all in standard units

Step 4: Substitute the values for total distance and time

Average speed = 100 ÷ 10.49 = 9.53288... = 9.53 m/s