How to Unstick Two Glass Bowls

Every so often you find two glass bowls stuck together in your cupboard. This happens because the air pressure between the bowls was different when they were stacked than the air pressure outside them. To break that seal without breaking the bowls, you will have to take advantage of physics. By applying heat to one bowl while keeping the other bowl cooler, you will force the warmer bowl to expand and the cooler bowl to shrink. Once this happens, the pressure is equalized and the bowls will come apart.

Things You'll Need

• Hot and cold water
• Basin or sink
• Five ice cubes
• Rubber mallet
• Thin-bladed knife
• Spray penetrating oil
• Wrap-around safety glasses
• Heavy leather gloves

Instructions

1. Place the two bowls in a basin or sink.

2. Fill the basin with hot, but not boiling, water until 1/2-inch below the edge of the bottom bowl.

3. Fill the top bowl with cold, but not icy, water.

4. Gently twist the bottom bowl from side to side. If it does not come loose, then empty both bowls and wait 5-10 minutes.

5. Refill the basin with hot water until 1/2-inch from the edge of the bottom bowl. Do not do anything to the top bowl. Gently twist the top bowl from side to side. If it does not loosen, then empty the basin.

6. Refill the top bowl with cold, but not icy, water and add five ice cubes. Wait 1 minute. Gently twist the top bowl.

7. If the bowls still will not come apart, then slip a narrow, thin-bladed knife between the two bowls. Don a pair of wrap-around safety glasses and heavy leather gloves. Spray with penetrating oil the place where the knife fits between the bowls, and then wait 5 minutes. Tap the knife blade gently with a rubber mallet, and attempt to twist the bowls apart.

Tips & Warnings

• According to the kinetic theory of matter, found on Mr. Hand's Eighth Grade Science website, "All matter is made up of atoms and molecules that are constantly moving. When heat is added to a substance, the molecules and atoms vibrate faster. As atoms vibrate faster, the space between atoms increases . . . the object expands and takes up more space. Solids, liquids and gases all expand when heat is added. When heat leaves all substances, the molecules vibrate slower. The atoms can get closer which results in the matter contracting. Again, the mass is not changed."

• Alex Helman, Ph.D,. in solid-state physics at the University of California Santa Cruz, has a photo tutorial of several experiments demonstrating various principles of thermodynamics, including one called "The Expanding Ball." According to Helman, "When both at room temperature, the ball fits through the ring. The heated ball will not pass through the ring."

References

• Mansfield, CT Schools
• Sirius-UCSC