Speed (Edexcel GCSE Physics: Combined Science)

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Calculating 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)

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

  • Where:
    • Speed is measured in metres per second (m/s)
    • Distance travelled is measured in metres (m)
    • Time taken is measured in seconds (s)

Person vs Bee, downloadable IGCSE & GCSE Physics revision notes

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

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)

  • The equation for calculating the average speed of an object is:

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

Average Speed Triangle, downloadable IGCSE & GCSE Physics revision notes

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)

Formula Triangle, downloadable AS & A Level Physics revision notes

How to use formula triangles

Worked example

Planes fly at typical speeds of around 250 m/s.Calculate the total 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 total distance

total distance = 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

total distance = 250 × 7200 = 1 800 000 m

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Ashika

Author: Ashika

Expertise: Physics Project Lead

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.