Speed

The speed of an object is a measure of how fast it is moving.Channel_TunnelTrain.jpg
(Velocity is the same value as the speed but also includes the object's direction.)

Speed tells us how far (the distance) the object moves in a certain time.
Because speed changes often over a journey, we usually mean AVERAGE speed.

If the distance is measured in kilometres and the time in hours the speed will be given in km/hr (kilometres per hour)

The formulas used to calculate the speed, distance and time are:

 


Y8_Speed_01.gif

This means
Speed = Distance ÷ Time

Example

A car travels from Christchurch to Dunedin a distance of 360 km.
The journey takes 4 hours. 
What is the average speed of the car?

Speed = Distance ÷ Time = 360 ÷ 4 =90 km/h

Y8_Speed_02.gif

 


Y8_Speed_03.gif

This means
Time = Distance ÷ Speed

Example

A plane flies from Auckland to Invercargill a distance of about 1600 km.
The average speed of the plane is 400 km/h. How long does the journey take?

Time taken = Distance ÷ Speed = 1600 ÷ 400 = 4 hours

 Y8_Speed_04.gif
Y8_Speed_05.gif 200 metres

 
Y8_Speed_06.gif

For an exciting and fun practice with these formulae −