# Speed

## Key Stage 3

### Meaning

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

The scientific units of speed are 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.

### Equation

$$Speed = {\frac{distance}{time}}$$

$$s = \frac{D}{t}$$

Where:

s = Speed
D = Distance
t = Time

### Example Calculations

 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 $$Speed = {\frac{distance}{time}}$$ $$Speed = {\frac{40000000}{5400}}$$ $$Speed = 7407.407m/s$$

## Key Stage 4

### Meaning

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.
The SI Units of speed are 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.

### Typical Speeds

You should remember the following speeds for everyday events:

 Motion Speed in m/s Average Walking Speed 1.5m/s Average Running Speed 5m/s Average Cycling Speed 10m/s Car on the Motorway 30m/s Propeller Plane Flying 100m/s Jet Plane Flying 250m/s Speed of Sound in Air 340m/s Speed of Light in a Vacuum 300,000,000m/s

### Equation

$$Speed = {\frac{distance}{time}}$$

$$s = \frac{D}{t}$$

Where:

s = Speed
D = Distance
t = Time

### Example Calculations

 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 $$s = \frac{distance}{time}$$ $$s = \frac{3600}{1680}$$ $$s = 2.142857m/s$$ $$s \approx 2.1m/s$$ distance = 42,000km = 42,000,000m time = 92min = 5520s $$s = \frac{distance}{time}$$ $$s = \frac{42000000}{5520}$$ $$s = 7608.7m/s$$ $$s \approx 7600m/s$$

### References

#### AQA

Speed, page 117, GCSE Physics, Hodder, AQA
Speed, pages 127, 147-149, GCSE Combined Science Trilogy; Physics, CGP, AQA
Speed, pages 134-141, 144-149, GCSE Physics; Third Edition, Oxford University Press, AQA
Speed, pages 140-1, 143-5, GCSE Physics; Student Book, Collins, AQA
Speed, pages 147, 178-180, GCSE Physics; The Complete 9-1 Course for AQA, CGP, AQA
Speed, pages 207, 225, GCSE Combined Science Trilogy 2, Hodder, AQA
Speed, pages 208, 210, 211, GCSE Combined Science; The Revision Guide, CGP, AQA
Speed, pages 60-63, GCSE Physics; The Revision Guide, CGP, AQA

#### Edexcel

Speed, pages 12, 14, 15, GCSE Physics; The Revision Guide, CGP, Edexcel
Speed, pages 145, 147, 148, GCSE Combined Science; The Revision Guide, CGP, Edexcel
Speed, pages 2, 12, GCSE Physics, Pearson Edexcel
Speed, pages 22-24, GCSE Physics, CGP, Edexcel
Speed; distance/time graphs, pages 27, 28, GCSE Physics, CGP, Edexcel
Speed; everyday speeds, page 23, GCSE Physics, CGP, Edexcel
Speed; measuring, page 41, GCSE Physics, CGP, Edexcel
Speed; of EM radiation, pages 127, 129, GCSE Physics, CGP, Edexcel
Speed; of sound in air, page 95, GCSE Physics, CGP, Edexcel
Speed; of water waves, page 96, GCSE Physics, CGP, Edexcel
Speed; of waves in a solid, page 97, GCSE Physics, CGP, Edexcel
Speed; orbits, pages 185, 186, GCSE Physics, CGP, Edexcel
Speed; wave speed, pages 93, 94, GCSE Physics, CGP, Edexcel

#### OCR

Speed, pages 157, 159-162, Gateway GCSE Combined Science; The Revision Guide, CGP, OCR
Speed, pages 21-24, 89-91, Gateway GCSE Physics; The Revision Guide, CGP, OCR
Speed; And acceleration, pages 51, 53, Gateway GCSE Physics, Oxford, OCR
Speed; And velocity, pages 50, Gateway GCSE Physics, Oxford, OCR
Speed; Calculation, pages 49, 195, 216-217, Gateway GCSE Physics, Oxford, OCR
Speed; Speed-time graphs, pages 56, Gateway GCSE Physics, Oxford, OCR