The heat wheel

After a short time, the grinder turns.

First, cut a square with a side length of about 15 cm from the paper. Then fold the square along the diagonals. The diagonals are cut about 8 cm from the corners. As shown in the sketch, make 5 small holes in the paper with the toothpick. First place a wooden bead on the toothpick and then the sheet of paper. Now place the perforated sides on the toothpick to create a windmill. Finally, the second wooden bead is placed on the toothpick and a stand for the straw is formed from the plasticine and then inserted. Finally, insert the toothpick with the windmill into the straw. Then light the tea lights and place them in a circle under the windmill.

• a few well-lit tea lights,
• 1 straw,
• Plasticine (a lump about the size of a table tennis ball),
• not too heavy paper,
• 1 toothpick,
• 2 small wooden beads that fit on the toothpick
• Scissors,

The windmill turns even with a small puff of air. Therefore, all windows should be closed and the students should keep a distance of approx. 1-2 m from the experiment so that they do not set the windmill in motion with the air they breathe. The windmill must stand upright. The tea lights must burn well. The paper should not be too heavy and should be folded properly so that the windmill can turn easily. The experiment should not be set up for longer than approx. 5 minutes, as otherwise the straw will slowly bend due to the heat generated and the windmill could fall into the candles and start to burn.

What is technically behind the experiment

The candle flame heats up the air, which rises and causes the mill to turn. The same thing happens with the Christmas pyramid. It is not the heat, but the rising air that makes the wheel turn. A similar phenomenon occurs with the windmill. Here it is the air moved by the wind that drives the mill.

Pupils should be made aware of the dangers of this experiment.

Carolin Sippel & Julia Ziegenbein