What you will need:
- Ping pong ball
- Small (clean) funnel
- Spool of thread
- 5” round disc cut out of card stock paper
- Adult supervision
1. Place the ping pong ball inside the funnel
2. Holding the funnel in a horizontal position, place your mouth over the small end of the funnel and blow as hard as you can.
3. As soon as you start to blow, let go of the ping pong ball
What is going on?
Surprisingly, the ping pong ball stays IN the funnel rather than shooting out as you would expect. This is due to air pressure. As you blow hard through the funnel, the air that is inside the funnel is moving rapidly. Bernoulli's Principal helps us to understand why this is happening. According to Bernoulli's Principal, faster moving air has less pressure. Since the air inside the funnel is moving really fast as it comes through the small end, wraps around the ball and eventually exits in a large area in front of the funnel, all of the air around the ping pong ball inside the funnel has less pressure than the air that is outside of the funnel. Since the air outside has more pressure, the ball is held inside the funnel where the pressure is greatly reduced.
Floating paper disc
1. Cut a 5” circle from a piece of card stock paper
2. Press a thumbtack through the center of the circle
3. With the thumbtack pointing up, place a spool of thread over the thumbtack so that the thumbtack is positioned in the center hole of the spool. Note that the thumbtack is not pressed into the spool and will move freely around the in the hole.
4. Place your mouth over the top end of the spool and blow hard.
5. As soon as you start blowing, raise the spool up as you continue to blow.
6. You will notice that the paper circle did not stay on the table and will seem to stick to the bottom of the spool.
7. As soon as you stop blowing, the paper will fall.
What is going on?
Again, this is due to the faster moving air causing a low pressure area. When you blow down through the spool, the air hits the top side of the paper and is diverted outward along the surface of the paper causing a low pressure area on TOP of the piece of paper. Since the air BELOW the paper is not moving, it remains at approximately 14.7 PSI (pounds per square inch) This higher pressure air underneath the paper will hold the paper up as it is drawn towards the lower pressure area above it.