The Kid Should See This

Thermal expansion sphere and ring demonstrations

If you ever had trouble twisting open a jar lid that’s stuck, try running it under some hot water. When you try again, it will most likely pop open with a twist thanks to thermal expansion. Most (but not all) matter will expand when heated and will contract when cooled. These metal sphere and ring video demonstrations showcase both phenomena.

In the North Carolina School of Science and Mathematics video above, the brass alloy sphere fits neatly through the ring at room temperature. What happens when the sphere is heated for a few minutes? explains:

Temperature is the average kinetic (or movement) energy of the molecules in a substance. A higher temperature means that the molecules are moving faster on average. If you heat up a material, the molecules move faster and, as a result, they take up more space – they tend to move into areas that were previously empty. This causes the size of the object to increase.

So when you heat up the jar lid, the same thing happens – the jar lid expands. So does the glass, but metals expand more than glass. The gaps between the metal jar lid and the glass threads increase, so it becomes easier to open.

Now see what happens when the ring is exposed to liquid nitrogen, cooling it down. This quick Thermal Expansion/Contraction (Ball & Ring) demo is from Saint Mary’s University’s SMUPhysics in Halifax, Nova Scotia:

Watch this next: What happens to balloon animals in liquid nitrogen?

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