1. Thermal Expansion and Contraction

2.  Have you ever wondered why this sign is posted at gas stations?  What would happen if you filled your gas tank completely? Thermal Expansion and Contraction

3.  Or why highways in the winter seem more bumpy?

4. Thermal Expansion and Contraction  Also why do the sidewalks have gaps?

5. Thermal Expansion and Contraction  Or why a full pan of water will overflow when you heat it?

6. Thermal Expansion and Contraction  And what are those teeth like things on bridges?

7. Arranging Molecules Thermal Expansion and Contraction

8.  Demonstration Arranging Molecules

9. Thermal Expansion and Contraction  Molecules are similarly arranged  The less they move the more of them can fit in a space  Adding heat or thermal energy (remember therm means heat) causes molecules to move more Arranging Molecules

10. Thermal Expansion and Contraction  This energy that makes molecules move is described as KINETIC ENERGY  Kinetic Energy = energy of movement Arranging Molecules

11. Thermal Expansion and Contraction  More energy = more movement  More movement = more space  Molecules will push out with a lot of force (well for them) to get that space Arranging Molecules

12. Thermal Expansion and Contraction  This “pushing” out is called THERMAL EXPANSION  Therm=heat Arranging Molecules

13. Thermal Expansion and Contraction  This works in the opposite as well  Take away heat (or thermal energy) you take away Kinetic Energy  Molecules move slower so they need less space  The result is shrink Arranging Molecules

14. Thermal Expansion and Contraction  So if adding Heat causes things to expand and taking it away makes them shrink  Let’s look back at our questions from earlier Arranging Molecules

15.  When gas is stored underground it is colder than you expect  On a hot summer day that gas will expand and if you filled you car up too much it would leak out! Thermal Expansion and Contraction

16.  Highways have gaps built into them so that when it gets hot they expand and seal the gap, in the winter though the road has shrunk and now the gap is noticable when you drive

17. Thermal Expansion and Contraction  Same thing with sidewalks, gaps are left so the cement has somewhere to go

18. Thermal Expansion and Contraction  Otherwise….

19. Thermal Expansion and Contraction  That water that fit before, well now it is taking more room which means it needs to get out of that pan

20. Thermal Expansion and Contraction  Bridges don’t have gaps, not good for crossing a space.  Instead they have expansion joints, that look like teeth

21. Thermal Expansion and Contraction  They give room for the bridge to grow but it is still connected the whole time  Also only one side of the bridge is anchored, the other side is only resting on a pillar

22. Hold on a second! Water when it freezes (gets colder) expands... Why is that?

23. Water breaking the rules  Water molecules when liquid flow very close to each other, in fact they are always constantly touching  But when it freezes they form crystals and leave gaps between themselves  Kind of like K’nex

24. Thermal Expansion and Contraction  Different materials expand and contract at different rates  That is because their molecules are connected differently from each other  Some have very strong connections so the molecules stay close, while others have loose connections  These are measured and given values called coefficients  Volume and length each have one, we will focus on length or linear for now

25. Thermal Expansion and Contraction  The larger the coefficient the more the material changes with heat  Make a chart in your notes to compare 7 common materials  Let’s start with Glass  Glass has a coefficient of 8.5

26. Thermal Expansion and Contraction  But there are different types of glass  Pyrex is a type of glass  Pyrex glass has a coefficient of only 3.2  Many scientist spend their time trying to develop new types of materials, thermal expansion is one thing they are working on

27. Thermal Expansion and Contraction  A common substance in homes is copper  It is used in wiring and pipes to hold water  It has a coefficient of 17

28. Thermal Expansion and Contraction  But in the winter if you are not careful water in pipes can freeze and burst the pipe  That is because water has a very high coefficient  69

29. Thermal Expansion and Contraction  Steel is used in bridges and skyscrapers  Engineers have to plan on how much the building will expand or contract  It has a coefficient of 11~13 depends on the type of steel

30. Thermal Expansion and Contraction  In homes windows need to allow light in but not the outside air  The glass has a low coefficient but it still changes enough to let in some  We put silicon caulk around windows to keep this from becoming a problem  Silicon has a coefficient of 2.56

31. Thermal Expansion and Contraction  Many times people end up getting rings stuck on their fingers  Our fingers react to the cold contracting as well but so will the gold in the ring  Gold has a coefficient of 14

32. Thermal Expansion and Contraction  Get familiar with these materials and their coefficients  Look for patterns that will help you determine how likely a material is to change  Hint: metals have higher coefficients than non-metals