demonstrations:inverse_square_law_with_balloon
Inverse Square Law With Balloon
Materials: ★☆☆ Easy to get from supermarket or hardware store
Difficulty: ★☆☆ Can be easily done by most teenagers
Safety: ★☆☆ Minimal safety procedures required
Categories: Astronomy and Space, Light
Alternative titles: Solar Power and Distance Demonstration
Summary
Students use an inflating balloon to model how light spreads out as distance from the source increases. By measuring how a square drawn on the balloon stretches with inflation, they visualize the inverse square law, which explains why spacecraft need larger solar panels when farther from the Sun.
Procedure
- Inflate a round balloon to about 10 cm in diameter and imagine the Sun at its center.
- Draw a 1 cm by 1 cm square near the bottom of the balloon with a marker. This square represents the amount of sunlight collected at a certain distance.
- Inflate the balloon to about 20 cm diameter, doubling the distance from the center. Measure the square again and record how its area has changed.
- Inflate the balloon further to about 30 cm diameter, tripling the distance from the center. Measure the square again and record the change.
- Compare the increase in balloon radius with the change in square area. Discuss how light intensity decreases as distance increases.
- Relate findings to solar-powered spacecraft and why their panels must grow in size as they travel farther from the Sun.
Links
📄 Collecting Light: Inverse Square Law Demo - NASA: https://www.jpl.nasa.gov/edu/resources/lesson-plan/collecting-light-inverse-square-law-demo/
Variations
- Compare results to actual missions like Juno, Psyche, or Europa Clipper and their solar array designs.
- Extend the demo to other forms of energy that follow the inverse square law (sound, gravity, radiation).
Safety Precautions
- Be careful not to over-inflate balloons, which may pop suddenly.
- Use caution when working with electrical equipment such as lamps or sensors.
- Keep markers and balloon fragments away from younger children.
Questions to Consider
- What happens to the available sunlight at Jupiter compared to Earth? (It is 1/25th as much, since Jupiter is 5 times farther away.)
- How does the inverse square law explain the need for very large solar panels on distant spacecraft? (Because the available light decreases rapidly with distance, requiring more collection area.)
- Does the inverse square law apply only to light? (No, it also applies to sound, gravity, radiation, and other forms of energy that spread out spherically.)
- How does the amount of sunlight at Saturn compare to that at Jupiter? (Saturn is twice as far as Jupiter, so light there is about 1/4 of that at Jupiter.)