Video: Watch this demo
Description: When you pull on the handle, the volume of the air pocket increases and pressure in the space decreases.
The decrease in pressure inside, balances with atmospheric pressure on the bottom and provides a connection strong enough to lift the stool.
- Stool with matching rubber mat.
- Wet the bottom of the mat and whip off the excess water (creates a better seal).
- Have a small student lift the mat off by one of its corners (easy).
- Have a strong student try and lift the mat off by the handle (hard).
- Note that they can’t lift the mat off, but they do lift the stool.
- If you draw a free body diagram for the stool, you have on top a lower pressure (since the volume of the air pocket increases and pressure decreases). On the bottom of the stool you have atmospheric pressure pushing up. The net force is up which is why the stool is lifted.
Note: Air slowly leaks in. To counter this, make sure the rubber is washed clean and slightly moist.