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The Challenge: Build accurate clocks

A siphon is the answer.

We placed a pipe into the upper barrel, partially filled with liquid. The pipe was then extended down to a lower barrel. To start the siphon, suction was needed at the bottom of the tube. A partial vacuum is formed at the bottom which allows atmospheric pressure to force water along the tube. This causes water to flow up the tube, over the bend (X), and along the tube towards the lower barrel.

Once the water reaches the same level as the end of the tube in the top barrel (point Y) the mass of water descending the pipe continues to draw more water from the upper container unaided. The longer the pipe descends from point Y, the faster the water will flow through the tube. The most important thing is that the rate at which the water flows is independent of the volume of water in the top barrel. It flows to the lower barrel at the same speed whether the top barrel is nearly full or almost empty.