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Science Experiment from the RMSC
Air Lift: The Bernoulli Effect
Ever wonder what helps an airplane fly? Airplanes use the air moving over their wings to help give them "lift." This is called the Bernoulli effect. Here are some experiments to help you discover how air gives "lift."
Equipment Needed:
paper
scissors
transparent tape
ping-pong balls
ruler
Flying Paper Strips
1. Using the ruler, measure and cut out strips of paper about 2 inches wide and 6 inches long.
2. Hold the shortest end just under your mouth, and blow over the paper. What happened? What do you think will happen if you change the size of the paper? Do you think the shape of the strip of paper is important? Try experimenting! Do you think the experiment will always work?
Swinging Ping-Pong Balls
1. Use the ruler and scissors to measure and cut two thin pieces of string 12 inches long.
2. Take a piece of string and tape one end of the string to a ping-pong ball.
3. Tape the other end of the string to the ruler.
4. Take the other piece of string and another ping-pong ball and repeat steps 2 and 3. The ping-pong balls should be hanging about one inch apart on the ruler.
5. Hold the ruler up so that the balls hang freely.
6. What do you think will happen if you blow in between the two balls? Try it!
Why?
Most people are surprised when the paper strips actually rise up! This is because the air you blow is moving faster than the air underneath near the bottom of the paper. That means there is more pressure underneath the paper than on top.
The same thing happens with the ping-pong balls. When you blow in between the two balls, the fast-moving air helps pull the balls closer together. The air traveling over the curved surfaces of the balls is faster, and therefore has less pressure than the air on the outside of the balls. Both balls move to where there is less pressure, so they move toward the middle and get closer together. The air pressure on the outsides does not increase, but the pressure in the middle decreases, making the balls swing toward each other. The balls are not "sucked" together. They were pushed together.
Likewise, with airplane wings, the curved surface of the wing causes the air to move faster over the top of the wing than the bottom. The faster moving air has less pressure than the slower moving air on the bottom of the wing. The greater pressure underneath pushes the wing upwards, giving it "lift."
This effect is called the "Bernoulli principle" after Daniel Bernoulli, a Swiss mathematician who lived in the mid 1700's. Bernoulli never really thought about flying. He was more interested in learning what causes changes in pressure. He died one year before the first balloon flight in 1783 and 71 years before the first winged glider flight in 1853.
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