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.)