Physics Lab · At-Home Setup
A very detailed, beginner-friendly walkthrough of the balloon method. Follow the diagrams top to bottom — each arrow shows exactly what to do.
When you rub two balloons, they both pick up the same kind of static charge. Same charges push apart (repel). If you hold one charged balloon below another, the push can be strong enough to lift the top one.
At the exact moment the upward electric push equals the downward weight of the top balloon, the forces are balanced. That balance lets a formula reveal the hidden charge:
Blow up both balloons to the same size — as big as is comfortable. Set one balloon on the scale and read its mass in grams, then divide by 1000 to get kilograms. Write it down as m (example: 2 g → 0.002 kg).
Rub each balloon hard on a wool sweater, fleece, or your hair — about 10–15 firm strokes. This is static electricity: rubbing moves tiny charges onto the balloon. Charge both balloons, and do it right before you measure.
Tape balloon #1 to the very end of the meter stick. Rest the stick on the edge of the table so most of it hangs off, like a see-saw, and put a heavy book on the table end to hold it down. The balloon end must be able to move up and down freely.
Hold the second charged balloon in your hand and slowly raise it straight up toward balloon #1 from underneath. As they get close you’ll see them push apart — that’s the electric force doing its job.
Keep raising balloon #2 until the push lifts balloon #1 so the meter stick becomes perfectly level (horizontal). At this exact moment the electric force up equals the weight down. Hold balloon #2 steady right here — don’t let it drift.
With your ruler, measure the distance between the centers of the two balloons at the balance point. Center-to-center — not the gap between their surfaces. Write it down as r in meters (example: 15 cm → 0.15 m).
Write down your m and r. Then do the whole thing again — five trials total — and recharge the balloons before each one, because the charge fades fast. You’ll end up with five values of r (m stays about the same).
Type each m and r into the Excel calculator I made — it fills in the charge q for every trial, plus the average and the uncertainty automatically. (Or do it by hand with the formula above.)
Expect an answer of roughly 0.1–0.5 µC (millionths of a coulomb). If you land there, your experiment worked and matches real static-charge values.
Balloon method (Lab handout Option #2) · pairs with your report + Excel calculator · If your instructor requires an IOLab force graph instead, use the foil-plate version.