Speed
Contents
Key Stage 3
Meaning
Speed is how fast something is moving, measured in metres per second.
About Speed
- 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:
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.
About Speed
- 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:
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