3/5/12 Part 3: Heat Temperature • Chapter 15: Temperature, Heat, & • Temperature (T) is a measure of how “hot” or “cold” something is Expansion • Temperature measures the random KE of • Chapter 16: Heat Transfer each particle in an object. • Chapter 17: Change of Phase – The greater the motion/vibration the greater the T – The smaller the motion/vibration the lower the T • Chapter 18: Thermodynamics • SI Unit: kelvin (K) – Room temperature is about 295K • Kelvin is the natural temperature scale – 0 K is lowest possible temperature – No negative temperatures – Random internal KE is zero at T = 0 K Other Temperature Scales Kelvin Temp. Scale • Celsius • The Kelvin scale has the same step size – Water freezes at 0ºC, boils at 100ºC (size of one degree) as the Celsius scale, • Fahrenheit but the Kelvin scale has its zero at – Water freezes at 32ºF, boils at 212ºF absolute zero. • Conversion between a Celsius temperature and a Kelvin temperature: Heat (Q) Definition of heat: • Heat is the energy transferred between objects because of a temperature difference. • Objects are in thermal contact if heat can flow between them. 1 3/5/12 Thermal Equilibrium Units of Heat • When the transfer of heat between objects • Since heat is just a flow of energy, the SI unit is the energy unit, the joule (J). in thermal contact stops, they are in • Other heat units thermal equilibrium. – calorie (cal): Heat needed to raise temperature of • The objects will then be at the same 1 gram of water by 1°C (or 1 K) – Calorie (Cal or kcal): Heat needed to raise temperature. temperature of 1 kg of water by 1°C (or 1 K) – Calorie also used to measure energy content of food Conversions: 1 cal = 4.186 J 1 kcal = 1 Cal (food Cal.) = 4.186 kJ Thermometers Specific Heat Capacity • Thermometers are instruments designed to • Specific heat capacity measure temperature. In order to do this, is the amount of heat energy required to raise they take advantage of some property of the temperature of one matter that changes with temperature. unit mass of a material – Length of a solid or liquid column by one degree. – Volume of a solid, liquid, or gas • SI Unit: J/(kg•K),or – Electromagnetic waves (infrared light) given off J/(kg•°C) by hot objects • Other Units: cal/(g •°C) Examples • Why does a piece of watermelon stay cool for a longer time than sandwiches do when both are removed from a cooler on a hot day? • Why is it that the climate in the desert is so hot during the day yet so cold at night? 2 .