To verify thermal expansion of metals
Most of the materials undergo thermal expansion when they are heated.
Bicycle spoke, candle, thin copper wire, empty refill
Bend the spoke in V shape. Pull both the ends a bit closer and fasten a copper wire taut between them. Put a piece of refill of suitable length between the two sides of the spoke. The refill should be placed such that it dislodges with the slightest increase in the gap. Heat the wire. Within a couple of minutes the wire expands and the refill fall.
Molecules (or atoms) of all the substances are in vibratory motion. When heated, the molecules become more energetic and require more space to vibrate. This result in thermal expansion.