Gravitational Attraction with an Ancient-Style Torsion Balance
Hard
Can you measure the tiny gravitational pull between two objects using only materials available in ancient times? A torsion balance detects this force by letting a suspended beam twist toward nearby masses.
You build a balance arm from a thin pine strip with lead weights at each end. Vegetable fibre from twine suspends the beam. Two large stone test masses (paving stones) are placed near the lead weights. The gravitational pull between the stones and lead causes the beam to twist slightly.
The challenge is the support fibre. Natural fibres respond to humidity and tear under stress. Selecting and preparing the right fibre takes patience and repeated testing.
Hypothesis
The hypothesis is that the gravitational force between two masses can be measured using Archimedes' Apparatus.
The pull that every object with mass has on every other object is real enough to measure on a tabletop — if you build the right instrument. A torsion balance detects this force by letting a suspended beam twist toward nearby masses. Build a balance arm from a thin pine strip with lead weights at each end, suspended by vegetable fibre from twine. Place two large paving stones near the lead weights. The gravitational pull between the stones and the lead causes the beam to twist slightly. The challenge is the support fibre — natural fibres respond to humidity and tear under stress, so selecting and preparing the right fibre takes patience and repeated testing.
A thin wire or fibre can detect forces too weak to feel — when a tiny pull acts on a suspended beam, the fibre twists just enough to measure. You build a balance arm from a thin pine strip with lead weights at each end, then suspend it from vegetable fibre cut from twine. Two large stone test masses (paving stones) are placed near the lead weights. The gravitational pull between the stones and the lead causes the beam to twist slightly, and the amount of twist reveals the strength of that force. Natural fibres respond to humidity and can tear under stress, so selecting and preparing the right fibre takes patience and repeated testing.
Method & Materials
You will use a balance arm, cradle, and support fibre to measure the gravitational force between two masses.
You will need a strip of pine wood, lead or gold weights, twine, and vegetable fibre.
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This experiment shows that the gravitational force between two masses can be measured using Archimedes' Apparatus. The most difficult component to replace with a 3rd century B.C. analogue was the support fibre, which required experimenting with a variety of alternatives and compromising with the shortcomings of whatever was selected.
Why do this project?
This science project is unique because it uses materials available in antiquity to measure the gravitational force between two masses.
Also Consider
Experiment variations to consider include using different materials for the balance arm and cradle, and using different test masses.
Full project details
Additional information and source material for this project are available below.
