This is the 3rd installment in the Simple Science Series. My goal with this series is to give you science experiments that you can do with the materials you already have in your house.
The video below shows one surprising experiment you can do with just a strip of paper. (I slowed down the second half of the video so that you can see the effect more easily. It also made Gideon’s voice sound funny.)
We tried this many times with different people blowing above the paper. Elijah wanted to put his hand under the paper. After he tried it, he remarked that there was no wind under the paper.
He was correct, and that is why this works. The air above the paper is moving and therefore its pressure decreases. The air under the paper continues to push with the same amount of force. Since the pressure under the paper is now greater than the pressure above the paper, it rises.
If you have a few balloons, you can also demonstrate the Bernoulli Principle this way.
When we blow between the balloons, we decrease the air pressure that is between them. The pressure on the outside stays constant, and the balloons are pushed together. This seems so counter-intuitive to me, which is one of the reasons it is important to let kids try these demonstrations in person.
One of the most common demos I have seen with the Bernoulli Principle is to use a fan or blow dryer to levitate a light ball (ping pong balls or beach balls).
I felt like our blow dryer was not very strong and did not work well with the ping pong ball. So I tried blowing up a water balloon (filling it with air). That was too light, so I tried another one with just a little water in it.
Then I had an idea for the first balloon.
So why is the Bernoulli Principle important?
It’s the physical principle that makes airplanes work. As the wing passes through the air, half of the air goes over the wing and half goes under it. The bottom of the wing is flat, so the air that goes under has a short distance to travel. The top of the wing is curved, so the air that passes over has to travel farther, in the same amount of time. This means that the pressure on the top decreases while the pressure on the bottom remains the same. So the force that lifts an airplane is the pressure that is always on the bottom of the wings. When the plane is moving, the pressure on the top of the wing is removed. That is pretty impressive considering that a Boeing 747 weighs about 900,000 pounds (408,00 kg).
This same principle gives lift to disc golf discs (or Frisbees) and is even used in sailing.
Have you ever seen a pitcher throw a curve-ball (or any breaking ball)? He is using the Bernoulli Principle! As the ball spins, the side of the ball that is spinning toward the batter builds air pressure because the seams push against the air, slowing it down. On the opposite side, the seams help push the air past faster thus decreasing the pressure. Since there is more pressure on one side of the ball, it gets pushed sideways.
I hope you enjoyed some simple science and the Bernoulli Principle. Check out the other posts in this series:
Sink or Float (I wrote this post a long time ago, so it was not part of this series, but it is another one that works with stuff from around the house.)