Heat

1. Heat Chapter 44 Page 296

2. Brainstorm! What can you tell me about heat?

3. Heat Heat is a form of energy Heat can be measure in Joules (J) because it is a from of energy What does energy do to an object? Heat can make things move

4. Where is the heat travelling in these pictures?

7. Heat Travels Heat will always move from a hot object to a cold object until both objects are the same temperature This can be done in 3 ways: • Conduction • Convection • Radiation

8. 1. Conduction Conduction is the transfer of heat through a solid without the particles in the solid moving out of position

9. Conduction (only occurs in solids) • Hot particles vibrate a lot • Cool particles vibrate a little

10. Conduction • Fast-moving particle (lots of energy) collide with neighbouring particles • This gives them more energy, making them vibrate faster

11. Conduction • This continues along the length of the solid until all the particles are vibrating with lots of energy

12. Conductors Metals are good conductors of heat They allow heat to travel through

13. Insulators An insulator is a substance which does not allow heat to pass through it easily Can you name any examples? They are measured using tog value, where have you heard this before?

14. Insulators

15. Insulators Why do you think insulation is important? Homework Design your own experiment

16. Today we will… • Conduct our insulation experiment • Look at method 2 of heat transfer : Convection

17. How are we going to conduct our experiment?

18. Which will be the best insulator? News Paper? Tea Towel? Cotton Wool?

19. 2. Convection Have you ever heard of this term before? Convection oven? Do you know how it works? Convection is the transfer of heat through a liquid or gas when the molecules of the liquid or gas move upward and carry the heat

20. To show convection in a liquid

21. To show Convection in a gas

22. Homework Question 3 Page 304

23. Today we will… • Correct Homework • Recap • Radiation as a method of heat transfer • Expansion and Contraction • Solid • Liquid • Gas

24. 3. Radiation Radiation is the transfer of heat in rays, from a hot object, without needing a medium to pass through All hot objects radiate heat This is how heat form the sun reaches the earth. It cannot travel by conduction or convection because of the empty space

25. Radiation The hotter an object is, the more heat it will radiate The heat radiated from an object also depends on the type of surface it has A dull black surface, radiates heat out better than a bright, shiny surface A dull black surface will also absorb heat better than a bright, shiny surface

26. To show heat transfer by Radiation

27. Radiation

28. Recap

29. Expansion and Contraction Why do we need to take the lid off a container before we heat Chinese leftovers in the microwave? Why does our deodorant can warn us to keep it away from direct heat? How do we make popcorn pop?

30. Expansion and Contraction Solids, liquids and gasses all expand when they are heated and contract when they are cooled. When atoms are heated, they vibrate/ jiggle, much faster and need to take up more space

31. To show the expansion of a solid

32. Where can we see this at work? The Bimetallic Strip Consists of a plate of iron and copper fixed together When heated copper expands more than the iron and so the bar bends. When it cools the bar straightens again

33. Why is this useful? They are mainly used to switch on and off an electric current It is used in simple fire alarms and any thermostat

34. To Show the expansion of liquids

35. Can a liquid also expand when cooled? Water is a special case Read about it on page 299 of book

36. To show the expansion of gasses

37. Conclusion Solids, liquids and gasses all expand when heated and contract when cooled

38. Homework Test on chapter of Heat next week!