Effect

A jar is filled three quarters full of water. A piece of laminated card is placed over the top of the jar and is tumed upside down. The card stays on under the jar. When the card is removed the water stays in the jar, defying gravity!

Method

Preparation

1. Place a glass jar upside down on a piece of fiberglass insect screen.

2. Trace the mouth of the jar onto the screen.

3. Carefully cut out the circle of screen. Note: The circle of screen should be slightly smaller than the outside of the jar’s rim.

4. Hot glue or superglue the screen to the top of the jar so that students cannot easily see the screen.

Procedure

1. Pour tap water through the screen until the jar is about three-quarters full.

2. Place a laminated card over the top of the jar and hold the card down tightly with one hand. The water will form an adhesive seal with the laminated paper.

3. Quickly invert the jar 180° over a sink or other container, such as a plastic tub or bucket.

4. While holding the jar steady, remove your hand from the laminated card. The card will remain in place over the mouth of the jar! The water forms a tight adhesive seal and external air pressure holds the card in place.

5. Carefully slide the card out from under the jar with one hand while holding the jar steady with the other hand. A little water may spill out, but most of the water will stay in the jar! The mesh screen provides a surface for the formation of hundreds of tiny surface-tension “membranes” that, in addition to air pressure, will support the weight of the water.

6. Tilt the jar a few degrees to allow air to enter the jar. The water will immediately spill out of the jar—gravity still works!

Note: To ensure the success of the trick, the glass is typically pressed against the surface quickly to create the low-pressure zone before any significant amount of water can start to fall out.

Tips and notes

There are variations that can be done on this demonstration. Rute has made jars with a metal lid that have a circle cut through it, with the insect mesh inserted in the top as shown in the video Anti-Gravity Water I.  If the mesh holes are large enough, wooden toothpicks can be pushed through the mesh and floated to the top of the bottle when turned upside down.

Magic shop shops will sell glasses called hydrostatic glasses which have a plastic insert which can placed over the mouth of the glass and have a hole drilled in the side of the glass. The glass is filled with water, the plastic insert is secretly placed over the mouth of the glass covered with a card and the glass is inverted (the hole should be covered with the thumb). When the card is removed, the water stays in the glass and can be released when the thumb is removed from the hole. A performance of this can be seen in the video Anti-Gravity water II.

This trick relies on scientific principles and clever manipulation of air pressure and water tension.

When the glass is turned upside down and pressed against a flat surface (e.g., a plastic sheet or piece of cardboard), the surrounding air tends to stick to the curved surface of the glass due to the Coanda effect.

When the glass is pressed against the flat surface the air pressure inside the glass becomes lower than the atmospheric pressure outside.

The water molecules create a surface tension that helps keep the water inside the glass. This surface tension, along with the low-pressure zone created by the Coanda effect, prevents the water from falling out of the glass, despite it being upside down.

The forces acting on the water in the glass are balanced due to the combination of surface tension and low air pressure inside the glass.