PURPOSE: To demonstrate properties of the siphon using a counterintuitive example.

DESCRIPTION: Two beakers with 600 ml of water are balanced on a platform suspended from a pivot. A siphon tube runs between the two beakers. The system is initially in equilibrium, with the platform horizontal, as seen by the arrow indicator at the center of the platform.

The following experiments may be performed using this apparatus:

• 1. What happens if extra water is poured into one of the beakers?
• 2. What happens if some water is removed from one of the beakers?
• 3. What happens if a small wooden block is placed on the platform by one of the beakers?
• 4. What happens if the wooden block is placed into one of the beakers so that it floats in the water?
• 5. What happens if an aluminum cylinder is lowered into one of the beakers so that it is suspended in the water without toucing the beaker?
• 6. What happens if the aluminum weight is allowed to rest on the bottom of the beaker?

SUGGESTIONS: If you can answer these questions correctly you understand equilibrium of torque and the operation of the siphon.

REFERENCES: (PIRA Unknown.) See Demonstration Reference File.

EQUIPMENT: Siphon balance prepared with 600 ml water each, spare water, small beaker for dipping water, wooden block on string, aluminum block on string with stand.

SETUP TIME: 5 minutes.