A Simple Frictionless Device for the Study of Motion.

The air-cushion table is a powerful instrument to demonstrate the motion of an object in the absence of friction. Such devices are often rather large and do not fit very easily in the classroom. In a different version of this experience, gas comes directly out of the disc itself, which is provided, for example, by a tank of dry ice that slowly sublimates. This second kind of device is more suitable for use outside the laboratory. On the basis of examples found on the internet, and with the aim of further simplifying usage, we produced a disc which exploits the air contained in a rubber balloon to reduce the sliding friction. We describe its features to enable teachers to reproduce it and analyse data extracted from pictures taken with a digital camera.