Overview
This lecture explains how sweating cools the body by examining the molecular processes behind evaporation and heat transfer.
Structure of Sweat and Skin
- Sweat is mostly water, made of Hâ‚‚O molecules (two hydrogens, one oxygen).
- The skin's surface contains molecules that make up skin cells.
Temperature and Molecular Motion
- Temperature measures the average motion (kinetic energy) of molecules.
- Higher temperature means molecules move, vibrate, or rotate more; lower temperature means less motion.
Heat Transfer from Skin to Sweat
- Muscles produce heat, which is transferred to the skin.
- Skin molecules have various kinetic energies and transfer energy to sweat molecules via collisions.
Evaporation Process
- Water molecules in sweat are attracted to each other by hydrogen bonds.
- Some water molecules move fast enough to break free and escape (evaporation).
- Evaporation removes the fastest, highest-energy molecules from the liquid.
Cooling Effect Explained
- When high-energy (fast-moving) molecules evaporate, the average energy of those remaining drops.
- Lower average kinetic energy means lower temperature for the sweat and the skin below it.
- This process results in a cooling sensation on the skin.
Key Terms & Definitions
- Kinetic Energy — The energy of motion in molecules.
- Evaporation — Process where high-energy molecules escape from a liquid into the air.
- Hydrogen Bond — Attraction between water molecules that helps hold droplets together.
- Temperature — The average kinetic energy of molecules in a substance.
Action Items / Next Steps
- Review the definitions of kinetic energy, evaporation, and hydrogen bonds.
- Be prepared to explain how evaporation leads to cooling at a molecular level.