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Mass vs weight

Science · Forces & Motion · ages 11-12

Name ______________________ Date ____________

Which unit is used to measure weight?
- kg
- N
- N/kg
Which action reduces a sample's mass?
- Removing some of its matter
- Moving it into a weaker gravitational field
- Moving it into a stronger gravitational field
- Measuring its weight in newtons
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. She travels to the Moon without gaining or losing matter. What is her mass there?
- 70 kg
- About 12 kg
- 0 kg
Zara travels between worlds without gaining or losing matter. She says, 'My weight is 500 N no matter where I go, because weight never changes.' What is wrong with her statement?
- Her weight stays 500 N; changing worlds changes neither quantity.
- Her mass stays the same; her weight depends on gravity.
- Her weight stays 500 N; her mass depends on gravity.
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 instead of the Moon's g.
- She multiplied the mass by g instead of adding them.
- Nothing went wrong; weight stays the same on every world.

Answer key

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

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N · Weight is a force, so it is measured in newtons (N), not kilograms.
Removing some of its matter · Removing matter reduces the amount of matter in the sample, so its mass decreases. Changing the gravitational field alone changes weight, not 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 · Changing location alone does not change mass. No matter was added or removed, so her mass remains 70 kg. The Moon's weaker gravity reduces her weight.
Her mass stays the same; her weight depends on gravity. · Zara gains and loses no matter, so her mass stays the same. Her weight depends on gravitational field strength and can change between worlds.
She used Earth's g instead of the Moon's g. · 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.