Overview
This lecture explains how sweating cools the body by focusing on water molecules, their motion, temperature, and the process of evaporation.
Sweating and Body Cooling
- Sweat is primarily composed of water molecules (H₂O) on the skin’s surface.
- The skin is heated by muscle activity, transferring heat to the sweat.
Molecular Motion and Temperature
- Temperature measures the average kinetic (motional) energy of molecules.
- Molecules can move (translate), vibrate, or rotate; higher energy means higher temperature.
- Not all molecules in sweat or skin have the same energy; some are faster, some slower.
Evaporation Process
- Water molecules in sweat are held together by hydrogen bonds.
- A molecule moving fast enough in the right direction can escape from the droplet—this is evaporation.
- Evaporation occurs when high-energy (high-speed) molecules break free from the sweat droplet into the air.
Cooling Mechanism
- The fastest (highest energy) molecules are most likely to evaporate.
- When these molecules leave, the average kinetic energy (temperature) of the remaining sweat decreases.
- Lower temperature in the remaining sweat lets it absorb more heat from the skin, cooling the body.
Key Terms & Definitions
- Kinetic Energy — energy due to motion of molecules.
- Temperature — the average kinetic energy of molecules in a substance.
- Evaporation — process where molecules escape from liquid to gas phase.
- Hydrogen Bonds — attractions between water molecules that hold liquid together.
Action Items / Next Steps
- Review definitions of kinetic energy, temperature, and evaporation for clearer understanding.