Physics Dept. Demonstration Manual

DF04 - Airflow Styrofoam Ball

Objective:

To demonstrate Bernoulli's Principle using air flow around a sphere.

 
Apparatus:  
  • Air blower (vacuum cleaner)
  • Two foot attachment with elbow and reducer
  • 3 inch "whitecaps" ball
  • hairdryer, funnels and stand

Method a:

The air blower is set horizontally, so it can roll in both directions a few cm. against wood blocks. The rigid pipe with elbow is attached vertically with the air blower stationary and stable, at midpoint between the two blocks. The ball is held in the airflow, about 30 cm. higher than the air outlet, and released. After initial oscillations the ball remains suspended in a meta-stable state. The air blower may now be rolled slowly, such that the discharge tube makes an angle of up to 45° with the vertical. Note that the ball remains captured in the airflow, at what appears to be an "impossible" angle.


Method b:

Use the hairdryer (see picture)

Note:

The decreased pressure "behind" the ball is sufficient to overcome gravitational effects.