AQA · A-Level · Physical Education
Course version: 7582 · Version from Sept 2016
Linear motion: Mass, speed and distance.
Mass, speed and distance are key scalar quantities of linear motion.
Checked against the AQA 7582 specification (opens in a new tab) on .
- Point 6 of 7
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Mass, speed and distance are key scalar quantities of linear motion. Mass is the quantity of matter in a body, measured in kilograms (kg), and it stays the same wherever the body is. Distance is the total length of the path travelled, measured in metres (m), and it has no direction. Speed is the rate of change of distance, measured in metres per second (m s⁻¹), and it also has no direction. These quantities are linked when calculating motion: speed = distance ÷ time. For example, a runner who covers 400 m in 50 s has an average speed of 400 ÷ 50 = 8 m s⁻¹. Because these quantities are scalars, a sprinter running 100 m in a straight line and a runner covering 100 m around a bend can both have the same distance and speed even though their directions differ.
What earns the marks
- Mass is the quantity of matter in a body and is measured in kilograms (kg).
- Distance is the total length of the path travelled and is measured in metres (m).
- Speed is the rate of change of distance and is measured in metres per second (m s⁻¹).
- Mass, speed and distance are scalars, meaning magnitude alone defines them without a specific direction.
- Speed = distance ÷ time.
- Average speed is total distance divided by total time, for example 400 m ÷ 50 s = 8 m s⁻¹.
- Mass is unaffected by gravitational field strength, unlike weight, which is a force in newtons (N).
Common mistakes and how to put them right
Confusing distance with displacement.
Put it right: Distance is the total path length, whereas displacement is the straight-line distance in a stated direction, so a 400 m lap finishing at the start has a displacement of 0 m.
Confusing mass with weight.
Put it right: Mass in kg is a scalar, while weight in N is a force equal to mass × gravitational field strength.
Using the wrong unit for speed, such as m.
Put it right: Speed is m s⁻¹ because it is distance in metres divided by time in seconds.
Assuming speed must include direction.
Put it right: Speed is a scalar, so a value such as 8 m s⁻¹ is complete without a direction.
Exam tips
- Read the option carefully to check whether it describes a scalar or a vector before selecting it.
- When a calculation is involved, write the equation speed = distance ÷ time, substitute the values with units, then state the answer in m s⁻¹.
- For average speed, use total distance and total time, not the speed at a single instant.
Try the lesson
The start of the Linear motion: Mass, speed and distance. lesson, made from checked teaching notes for this specification point.
Have a go first
A sprinter covers 100 m in a time of 12.5 s. Calculate the sprinter's average speed.
Listen
Mass, speed and distance are key scalar quantities of linear motion. Mass is the quantity of matter in a body, measured in kilograms (kg), and it stays the same wherever the body is. Distance is the total length of the path travelled, measured in metres (m), and it has no direction. Speed is the rate of change of distance, measured in metres per second (m s⁻¹), and it also has no direction. These quantities are linked when calculating motion: speed = distance ÷ time. For example, a runner who covers 400 m in 50 s has an average speed of 400 ÷ 50 = 8 m s⁻¹. Because these quantities are scalars, a sprinter running 100 m in a straight line and a runner covering 100 m around a bend can both have the same distance and speed even though their directions differ. A strong answer earns marks for these points. Mass is the quantity of matter in a body and is measured in kilograms (kg). Distance is the total length of the path travelled and is measured in metres (m). Speed is the rate of change of distance and is measured in metres per second (m s⁻¹). Mass, speed and distance are scalars, meaning magnitude alone defines them without a specific direction. Exam tip: Read the option carefully to check whether it describes a scalar or a vector before selecting it.
See it
Key words
Say what each word means before you turn the card.
Mass
Try answering aloud or in your head before turning the card.
Distance
Try answering aloud or in your head before turning the card.
Speed
Try answering aloud or in your head before turning the card.
Scalars
Try answering aloud or in your head before turning the card.
See every definition
- Mass
- The quantity of matter in a body, measured in kilograms (kg), and it stays the same wherever the body is.
- Distance
- The total length of the path travelled, measured in metres (m), and it has no direction.
- Speed
- The rate of change of distance, measured in metres per second (m s⁻¹), and it also has no direction.
- Scalars
- Quantities where magnitude alone defines them without a specific direction.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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