When the candle burns, chemical energy is converted into internal energy, which makes the air around the candle flame expand by heating, forming an updraft to do work on the windmill, converting internal energy into mechanical energy, and the windmill keeps rotating.

Extended data:

Examples of energy conversion in life

1, electric light-electric energy is converted into light energy and heat energy.

2. Friction generates heat-kinetic energy is converted into heat energy.

3. When the electric drill works, sparks are generated-kinetic energy is converted into heat energy.

4. Solar water heater-solar energy is converted into heat energy.

5, electric fan-electric energy is converted into mechanical energy and thermal energy.

6. Generator-mechanical energy is converted into electrical energy.

7. rice cooker-electric energy is converted into heat energy.

Baidu Encyclopedia-Energy Transformation