Mass vs weight

Science · Forces & Motion · ages 11-12

Name ______________________ Date ____________

Which unit is used to measure weight?
- kg
- N
- N/kg
Which of these is a weight, not a mass?
- 30 N
- 3 kg
- 300 g
- 0.3 kg
Which quantity is measured in N/kg?
- Mass, the amount of matter
- Weight, the pull of gravity
- Gravitational field strength
Which unit is used to measure mass?
- kg
- N
- N/kg
On the Moon, g is about 1.6 N/kg. What does a 35 kg bag of rock samples weigh there, in newtons?
Answer: ______________
If you know an object's weight and want its mass, you divide the weight by g.
Circle one: True False
On Earth, g = 10 N/kg. What is the weight, in newtons, of an object with a mass of 8 kg?
Answer: ______________
An astronaut's mass is 70 kg on Earth. What is her mass on the Moon?
- 70 kg (same as on Earth)
- About 12 kg
- 0 kg
Zara says: 'My weight is 500 N no matter where I go, because weight never changes.' What is wrong with her statement?
- Nothing, she is right, weight is always the same
- Weight changes with gravity; only her mass stays the same everywhere
- Actually mass changes, not weight
Ana works out the weight of a 60 kg robot on the Moon. She writes 60 x 10 = 600 N. What went wrong?
- She used Earth's g. On the Moon each kilogram is pulled with only 1.6 N.
- She should have added 60 and 10 instead of multiplying.
- Nothing went wrong, weight is the same on every world.

Answer key

For grown-ups. Fold this page away before handing over the rest.

N · Weight is a force, so it is measured in newtons (N), not kilograms.
30 N · Newtons measure force, and weight is a force: the pull of gravity. Kilograms and grams measure mass.
Gravitational field strength · N/kg is the unit of gravitational field strength, the number called g. Mass is written in kg on its own, and weight in N on its own.
kg · Mass is measured in kilograms (kg). Weight is measured in newtons (N).
56 · Weight = mass x g = 35 x 1.6 = 56 N, far less than the 350 N the same bag weighs on Earth.
True · Weight = mass x g, so going backwards means dividing: mass = weight / g.
80 · Weight = mass x g = 8 x 10 = 80 N.
70 kg (same as on Earth) · Mass never changes with location. Only weight changes, because gravity on the Moon is weaker.
Weight changes with gravity; only her mass stays the same everywhere · Zara mixed up mass and weight. Her mass stays constant everywhere, but her weight changes because gravity is different in different places.
She used Earth's g. On the Moon each kilogram is pulled with only 1.6 N. · Her method is right but her g is not. On the Moon g is about 1.6 N/kg, so the weight is 60 x 1.6 = 96 N.