Moon Drop: Does Mass Change Free-Fall Speed?
1 · Predict
On the Moon, a 1 kg ball and a 6 kg ball are released together from the same height, in a vacuum with no air resistance. Which one speeds up faster as it falls?
- The heavier (6 kg) ball speeds up faster
- Both balls speed up at exactly the same rate
- The lighter (1 kg) ball speeds up faster
2 · Set Up
- Open the Moon Drop preset. Note the two balls: a light one (1 kg) and a heavy one (6 kg), released together under the Moon's gravity (g = 1.6 m/s²).
- Select each ball in turn and set its mass in the properties panel to match the Mass column of the data table below before each run.
- Release both balls, pause the sim at the elapsed time listed in the Time column, and read the ball's downward velocity (vy) from the probe.
3 · Collect Data
| Mass (m) (kg) | Elapsed Time (t) (s) | Velocity (vy) (m/s) | Momentum (p) (kg·m/s) |
|---|---|---|---|
| 1 | 1 | ||
| 6 | 1 | ||
| 6 | 2 |
Plot vy (y-axis) against mass (x-axis) using rows 1 and 2. Then plot vy against time using rows 2 and 3. What shape is each graph, and what does it tell you about free fall on the Moon?
4 · Analyze
- Using your recorded vy and mass values, compute the momentum p = mv for each row. Show your work.
- Compare rows 1 and 2 (same time, different mass) and rows 2 and 3 (same mass, different time). What does each comparison tell you about how velocity depends on mass versus time?
5 · Extend
- Explain, using F = ma and weight = mg, why a heavier ball does not fall faster on the Moon — even though gravity pulls on it with more force.
- If this same experiment were done on Earth by dropping a feather and a bowling ball through air, would your data table look the same? Why or why not?
The Physics Behind This Experiment
Momentum
Momentum p = mv combines an object's mass and velocity into a single quantity — even though the light and heavy balls share the same fall speed at a given time, the heavier ball carries much more momentum.
Kinetic Energy
KE = ½mv² grows with the square of speed and directly with mass — so two balls hitting the ground at the same speed still carry very different amounts of kinetic energy if their masses differ.