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
- 14 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 14
Watch first
Gravity, mass and weight
An English teaching video on this topic from Lammas Science. Watch it, then scroll down for the lesson.
In a nutshell
Understand gravity force, weight and mass, and the relationship between them on Earth and other bodies
Learning cycle
Part 2 of 14
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 14
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.
Explore the idea
Part 4 of 14
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 5 of 14
Quick check
Which quantity stays the same wherever an object is in the universe?
Reset break
Part 6 of 14
Pause
That's sitting 1 of 2 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.
Quick check
Part 7 of 14
Quick check
A 10 kg object on Earth (g = 10 N/kg) weighs:
Learning cycle
Part 8 of 14
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 9 of 14
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 10 of 14
Quick check
Why does an astronaut weigh less on the Moon than on Earth?
Challenge round
Part 11 of 14
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 12 of 14
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).
Mastery quiz
Part 13 of 14
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 14 of 14
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 LunaDo the work
Your written work for this lesson
This is the part you'd do in your book at school. Pick the pieces below, write here or on paper, and photograph anything you draw or work out.
Why the school greenhouse failed
A science club grew tomato plants in the school greenhouse. In June the plants grew well: leaves were dark green and the fruit set quickly. In July the club went away for two weeks and left the greenhouse door shut. When they came back, the leaves were curled and pale and most of the fruit had dropped.
The club had a data logger inside. It showed the temperature reached 46 °C on several afternoons and the soil moisture fell close to zero. The club knew photosynthesis needs light, water and carbon dioxide, and that enzymes in a plant work best in a narrow range of temperature. Above that range the enzymes stop working properly.
The club repeated the summer with the door propped open and a water bottle drip on each pot. Temperature peaked at 31 °C and the plants survived.
Written for Good Learning Co.
Reading questions
- Name the variable the club changed the second time, and one variable they kept the same.
- Explain, using the words photosynthesis and enzymes, why the plants were damaged in July.
- Write a conclusion for the club's report, saying how far the evidence supports it.
Method and results
WritingWrite the aim, what you changed, what you measured and what you kept the same, then record your results in a table.
1 page + results table
Conclusion
WritingExplain what your results show and why, using the scientific words from the lesson. Say how you know you can trust them.
6–8 sentences
Labelled diagram
DiagramDraw the apparatus or the process in pencil, label it fully, and photograph it.
1 labelled diagram
Reading and notes
ReadingRead the lesson text again and write the key ideas in your own words.
Half a page of notes
Saved as you type.
Part 1 of 14 · Watch & discover
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Understand gravity force, weight and mass, and the relationship between them on Earth and other bodies