Work and Heat Chapter 16 Heat is the

Work and Heat – Chapter 16 – Heat is the transfer of thermal energy from one object to another through a temperature difference. – HEAT FLOWS FROM HOT TO COLD!!!!

A. Temperature • Temperature – measure of the average KE of the particles in a sample of matter – (how fast are the atoms/molecules moving? )

Temperature – measure of how hot or cold something is in relation to amount of kinetic energy an object has – SI unit for temperature is Kelvins (K)

Thermal Energy • Which beaker of water has more thermal energy? – B - same temperature, more mass 80ºC A B 200 m. L 400 m. L

Heat Transfer • Heat – thermal energy that flows from a warmer material to a cooler material • Like work, heat is. . . – measured in joules (J) – a transfer of energy

Conduction – Transfer of thermal energy when 2 materials TOUCH • Thermal conductors: conduct thermal energy well • Thermal insulators: conduct thermal energy poorly

Convection – Transfer of thermal energy through particles flowing around an object • Heat is circulating (Ovens, ocean currents) • OBJECTS NOT TOUCHING FOR HEAT TRANSFER

Radiation • Heat transferred through space as a wave of energy. • Ex. Heat/light from the sun. • Ex. Heat/light from fire.

Laws of Thermodynamics – 1 st Law: Energy can not be created or destroyed, it can change onto other forms – 2 nd Law: Heat can flow from cold to hot ONLY if you add WORK • Example: Refrigerator

Specific Heat Capacity • Specific Heat = the ability of a substance to absorb heat energy. (The number of calories needed to raise the temperature of 1 gram of the substance by 1 C. ) ***Specific Heat Capacity (c) Values are Constant. (Water has a cp of 1 cal/g x C) Thermal change (J)= Mass (kg) x T ( C) x Specific Heat Capacity (cal/g x C) Q= m T c

Specific Heat Practice Problems • Find the change in thermal energy of a 20 -kg wooden chair that warms from 15 C to 30 C if the specific heat of wood is 700 J/(kg C). • The air in a living room has a mass of 72 kg and a specific heat of 1010 J/(kg C). What is the change in thermal energy of the air when it warms from 15 C to 30 C?