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A vacuum cleaner is able to suck dirt off carpet because high pressure air from outside it flows toward low pressure air inside. In an electric vacuum, a fan causes air inside the vacuum to move quickly, which lowers the air pressure, causing suction. The higher-pressure air from outside the vacuum is sucked in to replace the low-pressure air, bringing dirt and dust with it to be caught in the filter bag. (Learn more about how vacuums work here.)
In this project you can make a hand-pump vacuum cleaner that alters the air pressure inside it and creates suction using a piston instead of a fan. Follow the procedure to make your vacuum, then read the explanation of how it works! An adult will need to help with the cutting.
1. Cut the bottom of the soda bottle off about 1/3 of the way up from the base. Now cut a slit down one side of the bottom third of the bottle - this will allow you to slide it inside the top part of the bottle so it can act as a piston.
2. Cut a 6'x3' strip of paper and fold it in half lengthwise for extra strength. Tape this strip to the bottom of the bottle to make a handle for your piston.
3. In the top part of the bottle, cut a 3/4-inch hole about 1-1/2 inches below the neck. This hole will lead to the filter bag.
4. Make a filter bag for your vacuum with a 6'x4' piece of tissue paper. Fold the paper rectangle in half and tape the sides to make a bag. Tape this over the hole you made near the neck of the bottle.
5. Tape one end of the thread to the ping-pong ball. Put the ball in the top part of the bottle. Feed the free end of the thread through the mouth of the bottle, and tape it to the outside of the bottle so the ping-pong ball hangs just slightly below the neck.
How does this contraption you just made work? Push the bottom part of the bottle into the top part, then pull it back sharply. This decreases the air pressure inside the bottle, because now there is a bigger space for the same amount of air. The lower-pressure air inside the bottle creates suction, pulling in higher-pressure air from outside in through the mouth. Now push the piston back in; this compresses the air and increases the pressure, so air flows back out of the bottle. The ping-pong ball works as a valve - when you push the piston in, it forces the ball into the neck of the bottle so that the air exits through the hole with the filter bag, rather than going out through the mouth.
Now put your vacuum to work! Try sucking up bread crumbs or tiny balls of paper. When you pull the piston out, they will be sucked into the bottle, and when you push the piston in, they will be forced into the filter bag.
Experiment to find out the best way to use your bottle vacuum. Does it work better to pump the piston rapidly? Should you pull out on the piston faster than you push in on it? Can you think of ideas to improve the design and efficiency of your vacuum? Give them a try!