An experiment to demonstrate terminal velocity
A tall glass jar or a tube fitted with a secure bung at its lower end about 5 em in diameter and 50 em in height is filled with glycerin and supported vertically (Fig. 13.16).
Small bearing balls handled with tweezers are then allowed to fall centrally down the tube by dropping them through a short piece of glass tubing which just dips into the glycerin. Balls of radius between 0.2 and 0.5 ern radius are suitable for this experiment, and they should first be whetted with glycerin contained in a small dish. This avoids the formation of small air bubbles which sometimes cling to the balls and spoil the results.
Terminal velocity will be reached after the balls have fallen some 7 or 8 em below the level of the glycerin. A wire band A to act as a marker is therefore placed about this distance below the glycerin level on the outside of the tube. Another, C, is placed near the bottom of the tube and a third, B, midway between them, thus dividing the liquid into two sections of equal height h. Using a stop clock, the time is noted as the balls pass each marker in turn. For a given ball it is found that the time intervals between A and B and between Band C are equal, showing that a steady terminal velocity was reached during the descent.