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Ball and Hoop
AKA: Thermal Expansion

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Fig 1: Ball and Hoop
Fig 1
Fig 2
Fig 3


A metal ball can pass through a metal hoop. When the ball is heated, it expands enough so it can no longer fit through.


This equipment consists of a handle with a hoop and a handle with a ball. At room temperature, the ball should easily fit through the hoop. If the ball is then held in a Bunsen flame for a minute or two, it cannot pass through the hoop.

Through heating, the metal expands in the same way railway tracks can become longer and buckle during hot summer weather. If the ring is heated to the same temperature it too will expand until the ball will go through once again.

In solids thermal expansion varies in line with the material’s 'coefficient of thermal expansion.' Polymers expand much more than metals, ceramics much less. Each metal expands to differing degrees.

The bar and gauge equipment shares the same principle (see Fig 3). Other thermal expansion equipment includes the bar breaking equipment and bi-metallic strips

This equipment is popular because it clearly shows the effects of thermal expansion very quickly. The ball and hoop sets are fairly inexpensive and are available through most lab suppliers.


 CautionThe ball and hoop will remain very hot long after heating takes place.

The contents of this page are for information only. Please refer to CLEAPSS or ASE safety advice and/or publications before undertaking any preparation, practical experiment or using any equipment featured on this site or any other.