Heat Heat Thermal Energy moving from a warm

Heat • Heat – Thermal Energy moving from a warm object to a cooler object • Heat can transfer or move in 3 ways – Conduction – Convection – Radiation

Conduction Heat transferred from one molecule to another without the object moving itself Always from Warmer to Cooler Usually Requires Contact

Convection • Heat is transferred by the mass movement of molecules from one place to another • Occurs within a Liquid or Gas

Warm, less dense water at bottom rises and is replaced with cooler, more dense water from above A circulation gets established called Convection Currents

Radiation • Conduction and Convection require a medium, like metal and water, to transfer heat from a hot region to a cold region • Radiation transfers heat through a gas or a vacuum: – Heat from the Sun – Heat from surface of a hot object

Electromagnetic (EM) Waves • Wave is transfer of Energy by vibration • Radiation is the transfer of Energy by a special type of wave called an Electromagnetic Wave • There are many types of EM waves and many applications: – – – Infrared we sense as Heat Visible light we sense as color X-Rays Radio & TV Cell Phone All Wireless devices

Conduction, Convection, and Radiation often occur together

Thermal Expansion & Contraction • As thermal energy of a substance increases, its molecules vibrate faster, spread out and the substance expands • As thermal energy of a substance decreases, its molecules vibrate slower, get closer and the substance shrinks • Matter expands when heated • Matter contracts when cooled

Interesting Demos on Conduction Convection Radiation