M4 Blow Hot Blow Cold

Background

Temperature of a substance is an indirect measure of the total kinetic energy of the particles of the substance. As kinetic energy is energy of motion, kinetic energy of a particle is an indirect measure of the speed of motion of the particles. So, higher the temperature, the higher the total kinetic energy of the sample of substance–sum of the kinetic energies of all the particles in the substance–and therefore higher the average speed of the particles in the substance.

When the substance under question is in the gaseous state, changes in temperature is accompanied by changes in the pressure the gas exerts.

Resources:

The Discrepant Event

Hold out your palm about 12 cm in front of your mouth. Blow on it with your mouth wide open. Make a note of how that feels on the surface of your palm. (It should feel warm.) Now, purse your lips and do the same. This time, the air hitting your palm should feel cool.

And the question is: Why is that?

Extension: Explain the sensations on the surface of the palm in molecular terms. (In other words, describe what’s happening on the surface at the molecular level.

Concepts involved:

  • temperature, body temperature, kinetic energy, speed/velocity, expansion, pressure (Additional advanced concepts: evaporation (at the molecular level), intermolecular forces, energy transfer/exchange, collision)

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