Why Don't Satellites Fall? Gravity, Orbital Motion, and Space Debris
Shared by A STEM Educator
Students will develop and use models to explain how gravity governs orbital motion (MS-PS2-4), analyzing patterns in planetary and satellite data to predict how changes in mass, distance, and velocity affect orbital paths — including the decay of space debris.
Lesson Overview
Students investigate the counterintuitive truth that satellites are always falling — they just keep missing Earth. Using real solar system data and satellite trajectory reasoning, students build a model connecting gravitational force, orbital speed, and orbital distance.
Materials
- Paper (any scrap paper for sketching)
- Pencil
- Whiteboard and markers (class-shared)
- Phone or basic calculator (for Task 3 data calculations)
- One textbook and one crumpled paper ball (teacher demonstration only)
Scaffolded Task Progression
A) On your paper, sketch what happens to the green (fast) path if Earth's surface curves away at exactly the same rate the cannonball falls.B) In one sentence, explain: what IS an orbit?C) Does the cannonball in orbit ever stop being pulled by gravity? Explain.
Using the data table below, plot Orbital Distance (AU) on the x-axis and Orbital Speed (km/s) on the y-axis on your graph paper. Connect the points with a smooth curve.
| Planet | Distance (AU) | Orbital Speed (km/s) |
|---|---|---|
| Mercury | 0.39 | 47.9 |
| Venus | 0.72 | 35.0 |
| Earth | 1.00 | 29.8 |
| Mars | 1.52 | 24.1 |
| Jupiter | 5.20 | 13.1 |
[ Interactive graph / diagram, available in the full lesson ]
A) Describe the shape of your graph. As distance increases, what happens to orbital speed?B) Earth's orbital speed is km/s. A GPS satellite orbits much closer to Earth than the Moon does. Predict: which one has a higher orbital speed — the GPS satellite or the Moon? Justify using your graph's pattern.C) A piece of space debris is in a low orbit (close to Earth). Based on the pattern, is it moving faster or slower than debris in a high orbit?
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