Illustration for article titled The drinking straw pump

This morning, we formally invite you to pump the orange juice out of your glass or the milk out of your cereal bowl with a pump made from a stick and a straw. Then spend the rest of the morning cleaning it up while whoever else eats breakfast near you glares at you reproachfully. Entertain them with a lecture about physics while you wield the sponge. It will be a rich, full day.


There's an easy way to get liquid to seemingly defy gravity and leap out of a bowl and spurt out into the air. All it takes is a couple of drinking straw segments positioned in the right way, and spun around in a circle. First you need a long stick, like a chopstick. Cross it with another chopstick near one end, like a Christian cross. Then secure two straws to the 'top' end of the cross, each going to one point of the arms of the cross. What you have should look like the frame of the sail on a child's drawing of a sailboat, with the straws forming the diagonal lines of the sail.

Turn the whole contraption upside down and put the tip of the 'sail' in the water and spin it around. Water should shoot out the tops of the straws rapidly. You've made a simple version of what's called a 'centrifugal pump.' Water rushed into the tips of the tilted straws when they're placed in the water. When the device is spun fast enough, the wall of the straw exerts more force on the water than gravity does. The water experiences a centrifugal force - it behaves as if it were being pushed outwards against the straw. It's a bit like a being on a public bus when the bus takes a quick turn, except the walls are tilted outwards. The water experiencing this push climbs the walls of the straws easily and squirts out the top. Meanwhile, more water rushes in to fill the void left behind by the departing water, refreshing the pump.


Other types of centrifugal pumps often using curved blades that rotate and push water through pipes. These are quite common in industry, since they don't use difficult-to-manage pressure chambers or back-and-forth motion to make the water flow. They just need one smooth device that spins in a continuous motion to provide a continuous pressure.

Image: Shebeko/Shutterstock

Via eHow, Robinson's Pump, Pumping Straw.

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