Ball and Funnel | Pōro me te Ipuroa Wahanui
A ball is supported and trapped in the air flow in an upside down funnel.
Fluid flow and Bernoulli’s Principle.
Te Reo Māori Version
Use the exhaust from a shop vac and practise first. The appropriate air flow is a strong function of the ball’s weight. For the hollow rubber ball we turn up the flow to nearly maximum, but only a small flow is needed for the ping-pong ball.
The airflow can contain dust and particles. Do not let students point it at a person’s face.
Individual teachers are responsible for safety in their own classes. Even familiar demonstrations should be practised and safety-checked by individual teachers before they are used in a classroom.
Notes, Applications, and Further Reading
Bernoulli’s principle tells us that the pressure is lowest in a fluid where the fluid is moving fastest (for points at the same height). This is reflected in Bernoulli’s equation for an incompressible fluid.
A ball can be suspended in the funnel by the downward air flow because the pressure near the top of the funnel, where air is moving fastest, is lower than the pressure near the bottom where air is moving slowest. The annotated videos below explain the demonstration in more detail. The Bernoulli equation is exact only under restricted conditions and will apply only approximately to air flow in these experiments.
This demonstration is related to PIRA 2C20.30.
This teaching resource was developed by the Te Reo Māori Physics Project with support from
- Te Puni Kōkiri
- The MacDiarmid Institute
- Faculty of Science, Victoria University of Wellington
- School of Chemical and Physical Sciences, Victoria University of Wellington
- The New Zealand map shown on the poster frame above is used with permission from www.nz.com.