Solution:The iron blade in a spade is fixed to the wooden handle by heating followed by cooling.
A substance expands; that is, the shape changes on heating and this phenomenon is called expansion. A substance shrinks; that is, the shape decreases on cooling, and this phenomenon is called contraction. The spade has an iron ring in which the handle needs to be fixed. The ring is smaller in size than the handle. The iron ring is heated, and it expands. As the shape of the ring changes, the handle easily fits into it. On cooling, the iron ring contracts and fits into the handle.