Average speed = distance/time
The speed of sound in air is about 330 m/s.
Scalar quantities have magnitude only.
Speed and distance are scalar quantities.
Relative speed is the speed an object is moving towards or away from another object, which may also be moving.

Common misconception

Pupils often do not have an understanding of what moving at a particular speed means in the real world, and treat answers as ‘just numbers’.

Use real world examples of speeds through examples and questions asked (N.B. 10 m/s is approximately 20 miles per hour).

Keywords

Average speed - The average speed of an object is the distance it travels each second (m/s). It is a scalar quantity.
Instantaneous speed - The instantaneous speed of an object is the speed at a particular moment.
Scalar quantity - Some quantities only have magnitude (size), and not direction. This includes distance and speed.
Magnitude - A scalar quantity only has magnitude (size).
Relative speed - The relative speed of objects is the difference in their speeds taking into account direction of movement.

Relative speed can be difficult for pupils to understand. Get them to form two lines and have one line walk past the other while the first is stationary, repeat for lines moving in the same and then opposite directions.

Teacher tip

Content guidance

Depiction or discussion of sensitive content

Supervision

Adult supervision recommended

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

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Starter quiz

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6 Questions

Q1.

Members of a running group compared their times to complete a park run. Use the times to put the runners in order of decreasing speed, starting with the fastest.

1 - runner E: 18 minutes

2 - runner D: 1140 seconds

3 - runner A: 20 minutes

4 - runner C: 1500 seconds

5 - runner B: half an hour

Q2.

Which of the following is not a valid unit for speed?

Correct answer: N/m²

m/s

kilometres per hour

mph

mm per min

Q3.

Match the activity to the typical speed for that activity.

Correct Answer:walking,1.5 m/s

1.5 m/s

Correct Answer:running ,3 m/s

3 m/s

Correct Answer:cycling,6 m/s

6 m/s

Correct Answer:travelling in a car,30 m/s

30 m/s

Correct Answer:travelling in a train,80 m/s

80 m/s

Correct Answer:travelling in a plane,500 m/s

500 m/s

Q4.

Two cyclists are racing up a hill. Cyclist A has a speed of 20 m/s and cyclist B travels 48 metres in 3 seconds. If the cyclists continue to travel at these same speeds, which statement is correct?

cyclist B will win the race

Correct answer: cyclist A will win the race

cyclist B has a higher speed

cyclist A has travelled 20 metres in 3 seconds

Q5.

Which of these distance–time graphs shows the motion of a stationary object?

Correct Answer: An image in a quiz

Q6.

The motion of two cars, A and B, has been displayed on a distance–time graph. Which statement about the two cars is correct?

A and B are travelling at the same speed

B is travelling faster then A

A and B are both stationary

Correct answer: A is travelling faster than B

Exit quiz

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6 Questions

Q1.

Match the key words or phrases to their definitions.

Correct Answer:average speed,the average distance travelled each second

the average distance travelled each second

Correct Answer:instantaneous speed,the speed of an object at a particular moment of time

the speed of an object at a particular moment of time

Correct Answer:magnitude,the size of a quantity

the size of a quantity

Correct Answer:scalar,a quantity that has only magnitude (not direction)

a quantity that has only magnitude (not direction)

Correct Answer:relative speed,the speed of one object compared to the speed of another object

the speed of one object compared to the speed of another object

Q2.

Match the activity to the typical speed for that activity.

Correct Answer:running,3 m/s

3 m/s

Correct Answer:walking,1.5 m/s

1.5 m/s

Correct Answer:cycling,6 m/s

6 m/s

Correct Answer:swiming,0.5 m/s

0.5 m/s

Q3.

A skateboarder travels a distance of 400 m in 50 s. What is their average speed?

350 m/s

20 000 m/s

450 m/s

Correct answer: 8 m/s

0.125 m/s

Q4.

Sound waves travel at 330 m/s in air. A boy sees a firework explode in the distance. The sound arrives 6.0 s after the flash. How far away from the boy did the firework explode (to 2 s.f.)?

55 m

Correct answer: 2.0 km

1.0 km

200 m

Q5.

Two cars are traveling in opposite directions (towards each other). The first car is travelling at 30 km/h and the second is travelling at 70 km/h. What is the relative speed of the cars?

30 km/h

70 km/h

40 km/h

Correct answer: 100 km/h

2100 km/h

Q6.

During a race, cyclist A is traveling at 10 m/s and is 200 m behind cyclist B, who is travelling at 8 m/s in the same direction. How long will it take cyclist A to catch up with cyclist B?

20 s

25 s

160 s

250 s

Correct answer: 100 s