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Thermal Energy

Thermal Energy. That’s so hot. All matter is made of tiny little particles (atoms and molecules) Those particles are never still. They always move, even if it is just vibrating in place Moving objects have KE!!. Temperature is the average KE of all the particles of an object.

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Thermal Energy

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  1. Thermal Energy That’s so hot.

  2. All matter is made of tiny little particles (atoms and molecules) • Those particles are never still

  3. They always move, even if it is just vibrating in place • Moving objects have KE!!

  4. Temperature is the average KE of all the particles of an object. • Measured in kelvins (K)

  5. Knowing this, what does it mean to increase your temperature? • It means that your particles have more KE, which means they are moving faster!

  6. Time for the people-are-molecules demo

  7. Thermal Energy (TE) is… • The sum of the kinetic and potential energy of all the particles in an object.

  8. When Temperature increases, so does TE, because temp. is the KE of the particles, and KE of the particles is part of TE!

  9. More mass also means more TE…why? • Because if you have more mass, you have more particles. More particles means more KE and PE to add together!

  10. Heat is TE that flows from higher temperature to lower temperature. • Since it is a form of energy, it can be measured in joules

  11. Objects do NOT transfer cold to each other, only heat! • Heat wants to move only from warmer objects to colder ones • Once temperatures are equal, no more heat is transferred

  12. Specific heat is the amount of heat it takes to raise the temperature of 1 kg of a substance by 1 K (same as raising it 1°C)

  13. Basic knowledge everyone remembers from high school science class: • Metals have low specific heats • Water has a very high specific heat

  14. What does it all mean?!?!?!?! • Look at page 161, Table 1 • Pretend you have 1 kg of water and 1 kg of iron • Put 4,500 J of TE into both, which one will get hotter?

  15. Coolants are used to cool things down. • Would you want your coolant to have high or low specific heat?

  16. If heat is the transfer of TE, then how does heat happen? • Three ways! • Conduction • Convection • Radiation

  17. Conduction is the transfer of TE by collisions between particles of matter.

  18. Let’s all play human conductor!!

  19. First, our volunteers start off as a solid (link elbows)

  20. Next, a liquid (unlink elbows, but stay close)

  21. Finally, a gas (spread out)

  22. ALL matter can conduct! • But solidsare better at it.

  23. Metals are the best conductors because: • They have loose electrons that can move freely within the metal and transfer TE much faster.

  24. Convection is the transfer of TE in a fluid by mass movements of matter. • Fluid: that which can flow (liquid and gas)

  25. Heated fluids rise above the cooler fluids surrounding them.

  26. The cooler fluid flows into the space the hot fluid was occupying

  27. The cooler fluid heats, then rises, and the cycle continues

  28. Radiation is the transfer of energy by electromagnetic waves. • Conduction and convection need matter to work; radiation does not!

  29. Radiant energy passes through most gases easily • Radiant energy can pass through or be absorbed by most liquids

  30. Most solids will absorb radiant energy • Yes, there are always exceptions to every rule...that is why I said ‘most’

  31. As said before, all matter conducts! • Some matter is really lousy at it • Those types of matter are called insulators.

  32. Insulators are substances that slow the transfer of TE from one place to another.

  33. One of the best insulators is air • Any material that has lots of air in it makes a good insulator

  34. Fiberglass traps air pockets

  35. Cotton insulationno itch!

  36. Special information: how a thermos works • They can keep warm stuff warm and cold stuff cold, but how?

  37. Combination of a vacuum and reflective surfaces

  38. Vacuum: • An absence of all matter, even air!! • If there is no matter, then there is no conduction or convection

  39. Reflective surfaces • On both the inner and outer wall of the vacuum space • Reflects most radiant energy

  40. THINK!!!! • If a substance gets hotter, its molecules move faster • Molecules moving faster will spread out

  41. When molecules spread out, they take up more space • This makes the entire object take up more space • This is thermal expansion • Also, the object becomes less dense

  42. Phase changes due to TE changes • Gaining TE can make a substance go from solid to liquid to gas • Losing TE can make a substance go from gas to liquid to solid

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