Equipment: A waiter's tray and a glass filled with water or "wine".

What it does: When the waiter's tray is swung in a full circle, the glass does not move and the water does not fall out.

Concepts Demonstrated: Forces in circular motion.

Classroom assembly:

1. Fill the glass with water or "wine" and place on the waiter's tray.
2. Swing the waiter's tray vertically, starting with a low amplitude and working up to large amplitudes.
3. Continue to increase the amplitude of the swing until the waiter's tray swings in a full circle.
4. Swing the waiter's tray in other directions for variety.

Cautions: Practice this demo in advance. Confidence and a smooth motion are requried. Do not hit your leg with the tray.

Setup Time: Short.

Difficulty: Straightforward after practice.

Visibility: High. This demonstration is appropriate for large lecture halls.

Related demonstrations:

References: PIRA 1D50.?

Original Construction: Purchased. The "wine" is water with red food colouring.

Background: This tray comes from Athens where it was used by a waiter in a restaurant to carry meals from the kitchen to the table. This demonstration is a nice example of the use of physical principles in daily life.