conduction

Meaning: Conduction is heat transfer through a material, or between materials in contact, by collisions of neighboring particles, with no bulk movement of the material. Faster particles in the hot region pass kinetic energy to slower ones, so energy flows from higher to lower temperature until thermal equilibrium. Metals conduct well partly because free electrons carry energy; gases, wood and foam conduct poorly. Conduction needs a medium, so it cannot cross a vacuum.

Equation: Q/t = kAΔT/L, where Q/t is the rate of heat flow in W (J/s), k is the thermal conductivity in W/(m·K), A is the cross-sectional area in m², ΔT is the temperature difference across the material in K, and L is the thickness in m.

On the MCAT: Expect questions on how the rate changes when thickness, area or material changes, on ranking conductors and insulators, and on why a metal object feels colder than a wooden one at the same temperature (metal moves heat away from your hand faster).

Common confusion: Conduction is not convection (energy carried by bulk fluid motion) or radiation (electromagnetic waves, which work in a vacuum). The rate depends on the temperature difference, not on the temperature itself, and on 1/L: doubling the thickness halves the rate.