Hydraulic machines have parts that are moved by liquid. Pneumatic machines have parts that are moved by a gas such as air. A hydraulic system has a pipe filled with a liquid, such as oil, and a piston that moves to and fro within the pipe. Pushing liquid into the pipe forces the piston to move, transmitting power from one end of the pipe to the other. In a simple pneumatic system, compressed air forces a piston to move.
In the first experiment, you make a simple hydraulic machine powered by water pressure. Water is poured from a central reservoir (pitcher of water) into a pipe. The water fills up a plastic bag. The bag expands and forces up the piston (the lid), which in turn raises a heavy object. Many cranes and trucks use this principle to lift heavy loads. In the air pump project, you discover the basic principles of how vacuum cleaner. Air is sucked in one hole and pushed out of another. A valve stops it from being sucked in and pushed out of the wrong holes.
YOU WILL NEED
- Make a hydraulic lifter:
Large plastic bottle, scissors, airtight plastic bag, plastic tube, tape, plastic funnel, spray can lid, heavy book, pitcher of water.
- Make an air pump:
Large plastic bottle, scissors, hammer, small nails, wooden stick or dowel, ruler card, tape, ping-pong ball.
Make a vacuum cleaner:
String, tissue paper, glue.
Make a hydraulic lifter
Cut the top off the large plastic bottle. Make sure the plastic bag is airtight, and wrap its neck over the end of a piece of plastic tube. Seal the bag to the tube with tape.
Fix a funnel to the other end of the tube. Make a hole at the base of the bottle, and feed the bag and tube through. The bag should sit in the bottom of the bottle.
Put the spray can lid on top of the bag, and rest a heavy book on top of the bottle. Lift the funnel end of the tube up, and slowly pour in water. What happens to the lid and the book?
Make an air pump
Cut around the large plastic bottle, about one third up from the bottom. Cut a slit down the side of the bottom part of the bottle, so that it will slide inside the top part.
Ask an adult to help you nail the bottom of the bottle to the end of a wooden stick or a piece of dowel. You have now made a piston for your air pump.
Cut a hole about ½in across near the neck of the bottle. Cut a piece of card about ¾ x ¾ inch. Tape one edge of the card to the bottle to form a flap over the hole.
Drop a ping-pong ball into the top part of the bottle, so that it rests in the neck. Push the bottom part of the bottle (the piston) into the top part (the cylinder).
Move the piston in and, to suck air into the bottle and out of the hole. Can you see how both the valves work? The flap should automatically close when you pull the piston out.
Make a vacuum cleaner
Make the air pump from the project above without the card flap. Tape string to the ball, feed it through the bottle’s neck, and tape it down, so that the ball is held near the neck.
Make a tissue paper bag and glue it over the hole near the neck of the bottle. Air from the pump will go through the bag, and anything the vacuum picks up should be trapped.
Try picking up tiny bits of paper with the vacuum. Pull the piston out sharply to suck the bits of paper into the bottle. Push the piston back in gently to pump the paper into the bag.
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