Speed

Key Stage 3

Speed is how fast something is moving, measured in metres per second.

Speed is commonly measured in the units of Miles per Hour, but this is not a scientific unit.

Other units of speed can be given by the units of distance used and the units of time used in the calculation of speed. If centimetres and minutes are used then the units of speed would be centimetres per minute.

Speed can be found by measuring the distance travelled by an object in a given time.

\[Speed = {\frac{distance}{time}} \] \[s = \frac{D}{t} \] Where:

A person jogs 300 metres in 120 seconds. Calculate the speed of the jogger.	A racing car travels 500 metres in 10 seconds. Calculate the speed of the racing car.
distance = 300m time = 120s \(Speed = {\frac{distance}{time}} \) \(Speed = {\frac{300}{120}} \) \(Speed = 2.5m/s \)	distance = 500m time = 10s \(Speed = {\frac{distance}{time}} \) \(Speed = {\frac{500}{10}} \) \(Speed = 50m/s \)

A horse takes 20 minutes to trot 2.4 kilometres. Calculate the speed of the horse in metres per second.	The International Space Station takes 90 minutes to orbit the Earth once travelling 40,000 kilometres. Calculate the speed of the ISS.
distance = 2.4km = 2400m time = 20min = 1200s \(Speed = {\frac{distance}{time}} \) \(Speed = {\frac{2400}{1200}} \) \(Speed = 2m/s \)	distance = 40,000km = 40,000,000m time = 90min = 5400s \(Speed = {\frac{distance}{time}} \) \(Speed = {\frac{40000000}{5400}} \) \(Speed = 7407.407m/s \)

Speed is a scalar quantity which describes the rate at which an object changes position.

Speed is a scalar because it has only magnitude but no direction.

Speed is commonly measured in the units of Miles per Hour, but this is not a scientific unit.

Other units of speed can be given by the units of distance used and the units of time used in the calculation of speed. If centimetres and minutes are used then the units of speed would be centimetres per minute.

Speed can be found by measuring the distance travelled by an object in a given time.

\[Speed = {\frac{distance}{time}} \] \[s = \frac{D}{t} \] Where:

A person jogs 315 metres in 120 seconds. Calculate the speed of the jogger correct to two significant figures.	A racing car travels 0.59km in 14 seconds. Calculate the speed of the racing car correct to two significant figures.
1. State the known quantities distance = 315m time = 120s	1. State the known quantities distance = 0.59km = 590m time = 14s
2. Substitute the numbers into the equation and solve. \(s = {\frac{D}{t}} \) \(s = {\frac{315}{120}} \) \(s = 2.625m/s \) \(s \approx 2.6m/s\)	2. Substitute the numbers into the equation and solve. \(s = {\frac{D}{t}} \) \(s = {\frac{590}{14}} \) \(s = 42.142857m/s \) \(s \approx 42m/s\)

A horse takes 28 minutes to trot 3.6 kilometres. Calculate the speed of the horse in metres per second.	The International Space Station takes 92 minutes to orbit the Earth once travelling 42,000 kilometres. Calculate the speed of the ISS.
distance = 3.6km = 3600m time = 28min = 1680s \(Speed = \frac{distance}{time}\) \(Speed = \frac{3600}{1680}\) \(Speed = 2.142857m/s \) \(s \approx 2.1m/s \| style="height:20px; width:300px; text-align:left;" \| distance = 42,000[[km]] = 42,000,000[[m]] time = 92min = 5520s <math>Speed = \frac{distance}{time}\) \(Speed = \frac{42000000}{5520}\) \(Speed = 7608.7m/s \) \(Speed \approx 7600m/s \)