What is the unit of weight?

newton. Weight is a force, so it is measured in newtons.

An object is taken from the Earth to the Moon. What happens?

Its mass stays the same and its weight decreases. The amount of matter is unchanged, but the Moon's gravity pulls on it less.

What does "gravitational field strength" mean?

the force on each kilogram. It is force per unit mass, in N/kg.

Mass, weight and gravity · Edexcel IGCSE Science (Double Award)

In plain words

Mass is how much stuff is in something, in kilograms, and it's the same wherever you are. Weight is the pull of gravity on that stuff, in newtons, and it changes if gravity does. On the Moon you'd have the same mass but weigh about a sixth as much.

Three things to know

Mass is how much matter an object has, in kilograms. It is the same everywhere.
Weight is the pull of gravity on that mass, in newtons. Weight = mass × gravitational field strength (W = mg).
On Earth g is about 9.8 N/kg. On the Moon it is about 1.6 N/kg, so the same mass weighs less there.

Worked example

What is the weight of a 3 kg bag on Earth? (g = 9.8 N/kg)

Weight = mass × g.
= 3 × 9.8 = 29.4 N.

Tips and tricks

Mass is in kg, weight is in N. If a question gives grams, change to kilograms first (divide by 1000).
In everyday talk people say "weight" when they mean mass. In a physics answer, never.

6 questions, about 2 minutes.

It lands in your notebook with its questions as flashcards.

Mass, weight and gravity: 6 questions and answers

These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.

What is the unit of weight?
- kilogram
- newton (the answer)
- newton per kilogram
- joule
Weight is a force, so it is measured in newtons.
A 3.0 kg bag hangs from a hook. Taking g as 10 N/kg, what is its weight?
- 0.3 N
- 3.0 N
- 13 N
- 30 N (the answer)
W = mg = 3.0 × 10.
An object is taken from the Earth to the Moon. What happens?
- Its mass and weight both decrease.
- Its mass stays the same and its weight decreases. (the answer)
- Its mass decreases and its weight stays the same.
- Neither changes.
The amount of matter is unchanged, but the Moon's gravity pulls on it less.
What does "gravitational field strength" mean?
- the mass of a planet
- the force on each kilogram (the answer)
- the speed of a falling object
- the weight of 10 kg
It is force per unit mass, in N/kg.
On Mars g is 3.7 N/kg. What is the weight of a 20 kg rover there?
- 5.4 N
- 23.7 N
- 74 N (the answer)
- 196 N
W = 20 × 3.7 = 74 N.
An object weighs 120 N where g = 10 N/kg. What is its mass?
- 12 kg (the answer)
- 110 kg
- 130 kg
- 1200 kg
m = W ÷ g = 120 ÷ 10.

6 questions

Tap an answer and you’ll see straight away whether it’s right, and why.

Worksheet

4 questions, 9 marks. Write your answers on paper, then check them.

Mass, weight and gravity

Edexcel International GCSE Science (Double Award) 4SD0 · 9 marks · papermunch.org

Name ______________________________ Date ______________

Calculate the weight on Earth of a 55 kg student. Take g = 9.8 N/kg.[2]
Show answerHide answer
539 N (540 N to 2 significant figures). W = 55 × 9.8.
I got this one
A rock weighs 49 N on Earth, where g = 9.8 N/kg. Calculate its mass.[2]
Show answerHide answer
5.0 kg. m = W ÷ g = 49 ÷ 9.8.
I got this one
An astronaut has a mass of 80 kg. On the Moon g = 1.6 N/kg. State her mass on the Moon and calculate her weight there.[3]
Show answerHide answer
Her mass is still 80 kg. Weight = 80 × 1.6 = 128 N.
I got this one
Explain why a balance that compares masses gives the same reading on the Moon as on Earth.[2]
Show answerHide answer
Gravity is weaker on the Moon, but it pulls less on both sides of the balance equally, so they still balance.
I got this one

Answers: Mass, weight and gravity

1. 539 N (540 N to 2 significant figures). W = 55 × 9.8.
2. 5.0 kg. m = W ÷ g = 49 ÷ 9.8.
3. Her mass is still 80 kg. Weight = 80 × 1.6 = 128 N.
4. Gravity is weaker on the Moon, but it pulls less on both sides of the balance equally, so they still balance.