A windmill uses the convective flow of heat to do useful work; it's a type of heat engine.
1. Wind is the result of convection currents between hot and cold regions on the earth's surface. What is the direction of the wind near the earth's surface in between a hot and cold region?
2. What is the direction of heat flow in between the hot and cold region on the earth's surface?
3. The temperature differences on the earth's surface produce ordered energy in the form of wind (the ordered part of the kinetic energies of the air molecules). Describe why this doesn't violate the second law of thermodynamics in terms of heat flow and entropy.
4. The windmill is simply a propeller blade on the end of a tall pole. The wind blowing at this propeller (along the line of the pivot) causes it to spin by producing a torque. Describe how a torque is produced by deflection of the air stream.
5. The wind has translational kinetic energy. When the windmill is spinning, what kind of energy does it have?
6. The energy of the spinning windmill can be used for many tasks such as generating electricity or pumping water. How does the amount of useful, ordered energy created by the windmill depend on the temperature difference between the hot and cold regions?
To keep cool on a hot day you sweat.
7. Why does the evaporation of sweat keep you cool?
8. Why do you cool off faster when the humidity (the amount of water vapor in the air) is low compared to when the humidity is high?