Take a sheet of paper. Draw a spiral on it as shown in the Fig. 4.14. Cut out the paper along the line. Suspend the paper as shown in Fig. 4.14 above a lighted candle. Observe what happens. Think of an explanation.

When the spiral paper is suspended at flame, then the paper spiral will keep moving because due to convection process, there will be transfer of heat and the air present above the flame will move up which results in movement of paper spiral.