One end of a steel girder in a bridge is not fixed, but is kept on rollers. Give the reason.

Describe an experiment to show that liquids expand on heating.

Describe an experiment to show that air expands on heating.

An empty glass bottle is fitted with a narrow tube at its mouth. The open end of the tube is kept in a beaker containing water. When the bottle is heated, bubbles of air are seen escaping into water. Explain the reason.