Weight and gravity in earth and other planets Simulation
Simulation Description
This interactive simulation demonstrates that weight is a force caused by a gravitational field, and that the weight of an object depends on the gravitational field strength at the point where it is located — not just its mass.
Students see a sphere representing a physical object falling, bouncing, and resting on the surface of seven different bodies in the solar system: Mercury, Venus, Earth, Moon, Mars, Jupiter, and Saturn. The simulation has two controls: a planet selector row at the top that switches between worlds, and a mass slider at the bottom that adjusts the object’s mass from 1 kg to 100 kg.
The canvas shows straight, parallel, downward-pointing field lines in the planet’s colour — the correct GCSE representation of a uniform gravitational field near a surface. Denser lines appear for worlds with stronger gravitational field strength, so Jupiter’s field looks visibly more intense than the Moon’s. A yellow weight arrow labelled W points downward from the object at all times, and its length scales with W = m × g, so the arrow visibly grows when mass increases or when the student switches to a high-g planet. The live formula display at the bottom shows the calculated values of W, m, and g updating in real time.
The drag interaction is the key teaching tool: students can lift the object to any height and release it, watching it fall and bounce. The same mass dropped on Jupiter falls noticeably faster and bounces lower than on the Moon, making the difference in gravitational field strength immediately visible. The object’s shadow on the ground also grows as it descends, reinforcing the sense of height and distance.
Class Activity — “Same Mass, Different Weight”
Level: KS4 / GCSE Physics (AQA, Edexcel, OCR) Time: 20–25 minutes Group size: Pairs or individuals
Learning objectives By the end of the activity students should be able to: distinguish between mass and weight; use W = mg to calculate weight on different bodies; explain why weight changes with location while mass does not; describe what gravitational field lines represent.
Part 1 — Predict (5 minutes)
Before touching the simulation, give students this table to complete as a prediction exercise:
| Body | g (N/kg) | Weight of 60 kg person (N) |
|---|---|---|
| Moon | 1.6 | ? |
| Mars | 3.7 | ? |
| Earth | 9.8 | ? |
| Jupiter | 24.8 | ? |
Students complete the Weight column using W = mg before opening the simulation. This activates the formula before the visual reinforcement.
Part 2 — Investigate (10 minutes)
Students open the simulation and set the mass slider to 60 kg. They cycle through each planet, record the weight shown in the formula bar, and check it against their predictions. Then they answer two observation questions: Does the object fall faster or slower on Jupiter compared to the Moon? Does changing the mass change how fast it falls? (Answer: no — all objects fall at the same rate under gravity regardless of mass, which the simulation shows because fall speed depends only on g, not on the slider.)
Students then drag the object to the top of the canvas, release it on the Moon, and repeat on Jupiter. They describe the difference in their own words.
Part 3 — Field lines (5 minutes)
Direct students to look at the background field lines. Ask: why does Jupiter show more lines than the Moon? Students should recognise that line density represents field strength — a denser set of parallel lines means a stronger uniform gravitational field. Ask: why are the lines straight and parallel rather than curved? Expected answer: near the surface the field is approximately uniform, so the lines are parallel. They would curve toward the centre only if we zoomed far out to see the whole planet.
Part 4 — Extension question (5 minutes)
An astronaut has a mass of 80 kg. Calculate her weight on Earth, the Moon, and Mars. She travels from Earth to Mars. What happens to her mass? What happens to her weight? Why does her mass stay the same but her weight change?
Discussion to close
Ask the class: if you could feel twice as heavy, does that mean your mass doubled? What would actually have to change? This reinforces the conceptual distinction — mass is the amount of matter (constant everywhere), weight is the gravitational force acting on that mass (varies with location and field strength).
Assessment hook
Exit card: students write the equation W = mg, define each symbol with units, and give one example of a situation where knowing the difference between mass and weight matters in real life (e.g. spacecraft design, landing on other planets, calculating fuel requirements).