Edexcel IGCSE Physics: Double Science 复习笔记:1.1.2 Speed

Edexcel IGCSE Physics: Double Science 复习笔记:1.1.2 Speed

Calculating Average Speed


  • The speed of an object is the distance it travels every second
  • Speed is a scalar quantity
    • This is because it only contains a magnitude (without a direction)




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 calculating the average speed of a moving object is:





  • The formula for average speed can be rearranged with the help of the formula triangle below:




How to Use Formula Triangles

  • Formula triangles are really useful for knowing how to rearrange physics equations
  • To use them:



  1. Cover up the quantity to be calculated, this is known as the 'subject' of the equation
  2. Look at the position of the other two quantities
    • If they are on the same line, this means they are multiplied
    • If one quantity is above the other, this means they are divided - make sure to keep the order of which is on the top and bottom of the fraction!





  • In the example below, to calculate speed, cover-up 'speed' and only distance and time are left
    • This means it is equal to distance (on the top) ÷ time (on the bottom)




Worked Example

Planes fly at typical speeds of around 250 m/s.Calculate the distance travelled by a plane moving at this average speed for 2 hours.


Step 1: List the known quantities

    • Average speed = 250 m/s
    • Time taken = 2 hours



Step 2: Write the relevant equation




Step 3: Rearrange for the distance moved


distance moved = average speed × time taken


Step 4: Convert any units

    • The time given in the question is not in standard units
    • Convert 2 hours into seconds:



2 hours = 2 × 60 × 60 = 7200 s


Step 5: Substitute the values for average speed and time taken


distance moved = 250 × 7200 = 1 800 000 m