Unit 6 Heat

What is heat? heat – form of energy in moving particles of matter

What is heat? at one time, people thought that heat was a physical substance called “caloric”

What is heat? in 1798, American scientist, Benjamin Thompson (Count Rumford) observed that mechanical energy could be converted to heat energy therefore, heat was not a physical substance but rather a form of energy

What is heat? heat energy makes the particles of matter move faster and further apart heat is a form of energy because it can do work adding or removing heat changes the temperature of a substance

Measuring Heat heat can be measured by observing the temperature change it causes when heat is added, the temperature of the substance rises when heat is removed from the substance, its temperature falls

Calories calorie – unit of heat; amount of heat needed to raise the temperature of 1 gram of water 1oC a calorie is a very small amount of heat

Calories calories are used to measure the amount of energy you get from food a food calorie is 1000 times larger than the calorie used to measure heat

Calories food calories are written with a capital C Calorie – 1000 calories, or 1 kilocalorie

Temperature heat is related to temperature but they are not the same

Temperature heat is the energy of the moving particles of matter heat is kinetic energy

Temperature temperature – measure of the average kinetic energy of the particles of the substance

Temperature as you remove heat from a substance, its particles move slower absolute zero – lowest possible temperature temperature at which particles of matter almost stop moving absolute zero is equal to -273OC

Temperature heat always moves from a place with a high temperature to a place with a lower temperature

Freezing Point freezing point – temperature at which a liquid changes to a solid every liquid has its own freezing point

Freezing Point the freezing point of water is 0OC when water freezes, it changes to ice

Melting Point melting point – temperature at which a solid changes to a liquid the freezing point and the melting point of a substance are the same

Boiling Point boiling point – temperature at which a liquid changes to a gas every liquid has its own boiling point

Boiling Point the boiling point of water is 100OC when water boils, it turns to steam

Evaporation evaporation – change from a liquid to a gas at the surface of the liquid when a liquid stands uncovered at room temperature, it slowly changes to a gas evaporation only happens at the surface of the liquid

Sublimation sublimation – change directly from a solid to a gas

Conduction conduction – heat transfer in solids heat travels by conduction when moving particles of matter bump into one another

Conduction conductors – substances that conduct heat easily most metals are good conductors of heat insulators – substances that do not conduct heat easily

Convection convection – heat transfer in gases and liquids

Convection convection currents – up and down movements of gases or liquids caused by heat transfer heat is carried through air and water by means of convection currents

Convection many homes are heated by convection forced air systems push heated air out of floor level vents to heat a room hot water heaters pump heated water through radiators near the floor of a room

Radiation radiation – transfer of heat through space space is a vacuum (empty space) so heat can not be transferred via conduction or convection

Radiation the earth receives heat from the sun via radiation

Radiation some home heating systems use radiation in a passive solar heating system, heat from the sun heats the house directly in an active solar heating system, heat from the sun is collected by solar panels, this energy is used to heat water which is then pumped through the house like in a regular system

Thermal Expansion thermal expansion – expansion of a substance caused by heating

Thermal Expansion most solids, liquids, & gases expand when they are heated and contract when they are cooled

Thermal Expansion an exception to this rule is the freezing of water as water cools from 4OC to 0OC, it expands rather than contracts this makes ice less dense than the surrounding water, causing the ice to float on the water