This chapter is from the book
This chapter is from the book
This chapter is from the book
Hand-Operated Water Pump (Archimedes' Screw)
How can water climb while "descending"? Doesn't it seem contradictory? Make your own water pump and find the answer.
Step By Step
Supplies
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PVC pipe 1.6 ft (0.5 m) long
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transparent plastic tubing, 1 yd (1 m) long
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masking tape
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2 bowls
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water
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water-based poster paint or food coloring
Twist the tubing around the PVC pipe and fix it in place with the tape, as the illustration shows. Fill one of the bowls with water (the pool) and place one of the ends of the pipe in it. The pipe needs to remain at an incline. The other end of the pipe should be higher up, leaning on the other bowl (the reservoir), so that the water from the tubing will empty into the reservoir. Hold the higher end of the PVC pipe and turn it with your hand. It will be easier to see what's happening if you put some coloring in the water in the "pool," perhaps water-based poster paint or food coloring, since they are safe and easy to clean up afterwards.
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Fun Facts
The tubing around the PVC pipe can be viewed as a collection of ramps wrapped around a central axle. As you turn the axle (PVC pipe), you carry water in successive lifts. As the water moves up, it is always on a ramp and "falls down" in order to locally minimize its gravitational potential energy. As you keep turning the wheel, the water moves on to a new ramp until it comes out at the top reservoir. The effort you have to make to pump water up with the Archimedes' screw is much smaller than that needed to lift the water vertically. It is just like walking on a road or path around a mountain up to the top. It requires less effort compared to climbing directly up the mountain, though the distance you have to walk is much longer. Now, try to lift water turning the axle (PVC pipe) the other way around. Will it work now? Why?
Alternative: Vertical Pumping H: Step By Step
Supplies
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2-quart (2-liter) plastic bottle
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marble
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1.6 ft (0.5 m) of transparent plastic tubing with inner diameter smaller than the marble diameter and outer diameter slightly larger, and a piece 1 /2 in (4 cm) long
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2 in (5 cm) of wider transparent plastic tubing that tightly fits the narrower one (if not, you can use electrical tape around it)
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food coloring (for contrast)
Insert the 1.6 ft (0.5 m) tubing into the 2 in (5 cm) tubing (if necessary, use electrical tape to obtain a tight fit). Place the ball in the wider tubing, on top of the 1.6 ft (0.5 m) tubing. The ball will act as a valve. Next, insert the 1 1/2 in (4 cm) long piece of tubing into the wider tubing, leaving some space for the ball to move up and down (if necessary, use electrical tape to obtain a tight fit).
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Operation of the Pump
Submerge the longer tubing in the bottle filled with water and move it quickly up and down, without the bottom part coming out of the water. At the same time, keep the opening at the top of the tubing partially covered with your thumb. See if you can get the water to gush out of the upper opening. You can adjust the space available for the ball by pressing the 1 /2 in (4 cm) long piece of tubing or pulling it out. Watch the column of water form in the clear tubing. You can use food coloring to better see what is going on.
Fun Facts
As you move the pump up, the ball keeps the top end of the longer tubing closed, while the air inside the tubing has more space—you produce a partial vacuum. Once the air pressure inside the tubing decreases, the water moves up (the same happens when you suck a beverage using a straw). When you move the tubing down, the ball is too sluggish to follow the tubing, so it lets the air out while more water comes into the tubing. By repeating this operation, more water fills the tubing until its only alternative is to gush out. Now, why do you need to partially cover the top of the pump with your thumb?