The Piggyback Balance Experiment: An Illustration of Archimedes’ Principle and Newton’s Third Law 1

The piggyback balance experiment is easy to perform and useful in teaching students about the opposition of the gravitational and buoyant forces. This can be especially useful for anyone engaged in high-accuracy gravimetric measurements. The experiment was conducted using an 85-g silicon crystal of known volume. The silicon crystal volume was 37.01596 cm³. The experiment was performed immediately after the balances were calibrated in situ with the standard weight. An ancient and useful method of volume determination was used to obtain the crystal volume from the observations made on each balance. There is the additional advantage of teaching the importance of the ancillary measurements to achieve accurate results. This is especially true of the volume determination.