The Shape of a Raindrop



Many illustrations of rain show drops in a teardrop shape. Since raindrops fall at around 9 meters per second, 18 feet per second, it is tough to see one as it falls. A vertical wind tunnel which blows air upward can be used to let people easily look at the shape of a drop as it falls.

Attach a piece of plastic tube to the exhaust port of an old vacuum cleaner fan as in the diagram. Cut one (or more) round pieces of screen and support them in the center tube with wire. Mount the setup so the air flow is directly upward. Plug the vacuum cleaner fan into a variable transformer (variac) and use the knob on the variac to adjust the air flow so a drop just hangs in the center of the upward moving air. The demonstration takes some fussing with to set it up so the drop is stable on the air stream. If drop doesn't stay on the air column, a second baffle screen may be needed. A hair drier set on "cold" or with the heater removed may work as well.

see caption above