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Measures : Key Stage 4 : Mathematics Content Knowledge

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Key Stage 4
Question 1 of 12

1. How confident are you that you understand

a. the distinction between mass and weight?


Mass is the quantity of matter in an object, measured, for example, in grams and kilograms. Technically this is not the same thing as weight.

Weight is the force of gravity acting on an object and is therefore properly measured in newtons. It varies depending on how far the object is from the centre of the Earth. Colloquially, ‘weight’ is used as a synonym for ‘mass’.

When we weigh an apple and say it weighs 100 grams, we really mean that it weighs the same as a mass of 100 grams. But what we experience when we hold the apple in our hand is its weight, i.e. the force of gravity upon it; we exert a similar force on it to hold it up.

What this might look like in the classroom

Question 1:
Suggest suitable units for measuring the mass of:
  1. a car
  2. a person
  3. an egg

Answer 1:
  1. tonnes
  2. kilogrammes
  3. grammes

Taking this mathematics further

Physicists in particular work with the distinct difference between mass and weight. Why is this? How does this connect to an understanding of the force acting on an object?

Newton's second law is F = ma
where F is the force m the mass and a the acceleration
So if we pushed a mass of 1kg with a horizontal force of 10 newtons. The mass would move with an acceleration of 10 m/s2.

Making connections

Colloquially we often use “weight” when we actually mean “mass”. However, it is important to distinguish between mass and weight and to use them in the correct contexts.

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