Gravity, mass and weight
Your mass never changes wherever you go in the universe, but your weight depends entirely on how strong the local gravity is.
Part of your national curriculum
- Physics: space physics: Understand gravity force, weight and mass, and the relationship between them on Earth and other bodies
Lesson overview
What you'll learn in this lesson
Understand gravity force, weight and mass, and the relationship between them on Earth and other bodies
Key learning points
- • Mass versus weight
- • The weight equation
- • Gravity between bodies
This lesson at a glance
- 24 minutes
- 17 parts to scroll through
- 3 quick checks
- Marked quiz at the end
- Gentle pace: short sittings with pauses
Words to know
Scroll down — the lesson carries on below
Watch & discover
Part 1 of 17
Visual introductionPicture this
Gravity, mass and weight
Your mass never changes wherever you go in the universe, but your weight depends entirely on how strong the local gravity is.
In a nutshell
Understand gravity force, weight and mass, and the relationship between them on Earth and other bodies
Learning cycle
Part 2 of 17
Learning cycle 1 of 2
Part 1 · Mass versus weight
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 3 of 17
Learn
Mass versus weight
Mass is the amount of matter in an object, measured in kilograms (kg), and stays the same everywhere. Weight is the force of gravity acting on that mass, measured in newtons (N), and depends on the local gravitational field strength.
Reset break
Part 4 of 17
Pause
That's sitting 1 of 4 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Explore the idea
Part 5 of 17
Learn
The weight equation
Weight = mass × gravitational field strength (W = m × g). On Earth, g ≈ 10 N/kg, so a 5 kg object weighs 5 × 10 = 50 N. On the Moon, where g ≈ 1.6 N/kg, the same 5 kg object weighs only 5 × 1.6 = 8 N.
Quick check
Part 6 of 17
Quick check
Part 7 of 17
Reset break
Part 8 of 17
Pause
That's sitting 2 of 4 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Learning cycle
Part 9 of 17
Learning cycle 2 of 2
Part 2 · Gravity between bodies
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 10 of 17
Learn
Gravity between bodies
Gravity is a force of attraction between any two masses; larger masses and shorter distances create stronger gravitational forces. This is why the Moon orbits the Earth, and why gravitational field strength differs between planets of different mass and size.
Quick check
Part 11 of 17
Reset break
Part 12 of 17
Pause
That's sitting 3 of 4 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Challenge round
Part 13 of 17
Game · Sort it
Which of these are true?
Drag each card into the right column. Tap a card first if dragging is fiddly.
True
Not true
Challenge round
Part 14 of 17
Game · Fill the gaps
Finish the sentences
Choose the word that belongs in each gap.
Weight is the force of ____ acting on that mass, measured in newtons (N), and depends on the local gravitational field strength.
____ = mass × gravitational field strength (W = m × g).
Challenge round
Part 15 of 17
Game · Recall cards
Which quantity stays the same wherever an object is in the universe?
Card 1 of 3
Mastery quiz
Part 16 of 17
Marked quiz
End of lesson quiz: Gravity, mass and weight
3 questions, marked with the reasoning shown. No timer.
1. Which quantity stays the same wherever an object is in the universe?
2. A 10 kg object on Earth (g = 10 N/kg) weighs:
3. Why does an astronaut weigh less on the Moon than on Earth?
Lesson round-up
Part 17 of 17
Lesson round-up
Ready when you are
Quiz score
Not sat
Games
Not played
Points this lesson
0
Best run
0 in a row
Luna: 0 out of 3 on the practice checks. Only if you feel up to it — one more?
Ask LunaPart 1 of 17 · Watch & discover
How this is going
- Not looked at yet
Understand gravity force, weight and mass, and the relationship between them on Earth and other bodies