Physics with a leaf blower.

Principle Demonstrated: Bernoulli’s Principle, Balanced forces

Materials:

• Leaf blower
• Beach ball
• Air pump to inflate the beach ball.

The demonstration.
Whan doing a demonstration I like to have the students do three steps as part of the demonstration.
  I.   Observe
  II.  Infer
  III. Calculate

Observe the demonstration. If possible I'll have hte students be a part of the demonstration.
Infer the concepts behind the demonstration
Calculate: when possible have something to calculate or even better to measure and calculate.

Inflate the beach ball using a pump. Don’t use your breath.  If the ball pops you spit will go everywhere. Also, once the air inside cools, the spits will condense inside. This does not looks particularly good in a transparent or translucent beach ball.

Hold the blower such that it is blowing upwards at  30° with the vertical. Have a student hold the beach ball high and walk it into the air stream until the ball lifts out of the student’s hands.

The beach ball can be moved around by changing the direction of the sire stream.

Video
Watch Steve Spangler do this demo the toilet paper demo below.
http://www.youtube.com/watch?v=D6WLC-Z0Brs

Follow Up:
Ask the students to write down their observations. It helps to have a picture of the ball so they can see what is going on.
Then ask the students to infer why the ball behaves I that manner.

What it demonstrates:
If you look carefully at the ball, at some point it will stop oscillating up and down. The ball sits a little lower than the middle of the air stream from the blower. In this position the air must be traveling faster over the top than underneath it. The lifting fo5pxce is equal to the weight of the ball.

Extensions
The ball will oscillate up and down, ask student to infer as to why this is happening.

Instead of using a beach ball, try a two-liter bottle with a little water in it. Hold the bottle in the air stream with the cap towards the ground.

PowerPoint™ slideshow with some images that might help in its presentation. (Zip file)

KeyNote™ slideshow with some images that might help in its presentation. (Zip file)