Speed (Edexcel GCSE Combined Science) : Revision Note

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)

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:

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)

How to use formula triangles