1. Unit 6
Heat

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

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

4. 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

5. 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

6. 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

7. 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

8. 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

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

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

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

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

13. 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

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

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

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

17. 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

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

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

20. 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

21. Sublimation
sublimation – change directly from a solid to a gas

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

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

24. Convection
convection – heat transfer in gases and liquids

25. 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

26. 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

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

28. Radiation
the earth receives heat from the sun via radiation

29. 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

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

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

32. 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