Air Speed and Pressure
Combining environmental studies and science projects, we decided to see what kind of power can be obtained from a fruit.
1. We actually did use a real carbon rod and some zinc for the terminals but these materials are not easily obtainable. Alternatively, you can use a zinc coated nail (galvanised) for the zinc and some copper wire instead of the carbon rod. Stick them well into the lemon.
2. Connect up the wires to the Voltmeter as shown in the diagram. We managed to get 1.2 Volts from the lemon. If you cannot get a voltmeter, wrap a few coils of wire around a compass and connect the ends to the carbon and zinc in the lemon. The compass needle should deflect slightly each time the wires are connected. Other fruits work as well.
The Wright brothers and several others were aware of the following law:
It is this law that allows airplanes to fly- the air pressure over the wing being less than that under the wing.
To demonstrate this law, set up a glass of water full to the brim or as close as you can get. There probably isn't quite enough water in the glass in the picture. Place a straw in the water and at the same time set up a second straw at right angles to the first. When you blow through the second straw, water should be sucked up through the first straw and spatter out the top.
When you blow through the second straw you are increasing the airspeed across the top of the first straw, thereby reducing the air pressure just at this point. The air pressure on the surface of the water is greater than that at the top of the straw. This causes the water to rise through the straw.