What you need:
A hair dryer
A ping pong ball
What to do:
1. Switch on the hair dryer and point its nozzle upwards to the ceiling.
2. Place the ping pong ball in the jet of air being released by the hair dryer.
3. Keep an eye on the ball. When it becomes steady, slowly start tilting the hair dryer nozzle to the left and the right. What do you see?
What happens:
When you tilt the hair dryer, the ball moves with the stream of air. As long as you move the hair dryer slowly, the ball continues to hang in its jet
Why?
Daniel Bemoulli, an 18th-century Swiss mathematician and physicist, is remembered for giving us something known as Bernoulli’s principle that applies to moving fluids (since air flows, it is also considered a fluid). According to this principle, the faster the air flows over a surface, the less it pushes on the surface Le the pressure exerted by the air on that surface decreases
Think of it like this: If you’re moving fast through a crowd, you don’t stop to push and shove people in your way. That would just slow you down. To keep moving fast, you step around the people, maybe just brush against them. That means you exert less pressure on the people in your path. Air does that too.
The hair dryer shoots out fast-moving air. When the ping pong ball is placed in the path of this first-moving air, the air molecules exert low pressure on the ball because they are shooting up really fast. But the air above the ball is not moving much. So it has higher pressure. This high pressure doesn’t allow the ball to shoot up and away. And gravity tries to pull the ball back to the ground. But that is countered by the upward current of air from the dryer. So all the forces balance out and help hold the ball steady
Once the ball is steady, you start moving the dryer sideways. Now, the air is moving really fast around the ball in the stream but the rest of the surrounding air is stationary. That is why it exerts higher pressure on the ball pushing it back whenever it tries to leave the low pressure jet. So, the ball stays in the stream of the dryer, suspended, as long as you move the dryer slowly. You can even challenge your friend and see who is able to keep the ball hovering longer.
Picture Credit : Google
