Siphon Experiment

The kids really enjoyed our science experiment today. We used a length of clear plastic tubing about two feet long, a drinking cup, and water from our bathroom sink.

First we played with the tube in water. We filled the cup with water.
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They put the tube in the cup straight up. Nothing happened to the water.
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They put one end of the tube in the cup and bent it down toward the sink.
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Again nothing happened to the water.
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We emptied the water out of the cup and refilled it. This time we started out with the tube in the cup and filled it by running the water through the tube. Cameron really liked this experiment so he repeated it several times, changing little things each time to see if it changed the outcome. He discovered the end result is much better and faster if you use warm water instead of cold to fill the cup through the tube.
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Once the cup was 3/4 full, we quickly covered the end with a thumb so no air could escape.
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We carefully moved the cup with the tube bent down to the sink to the side of the sink with the thumb still over the end.
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Finally, we uncovered the end of the tube and watched as the tube acted as a siphon to bring the water up and out of the cup.
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This works because as the water already in the tube runs out downhill it pulls the water behind it. Air pressure in the atmosphere pushes the water into the tube from the cup so the siphon keeps flowing.

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