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Heat Transfer What is a heat? Heat always flows away from a hot material to a cold material Remember, heat moves in predictable ways, from a high temperature.

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Presentation on theme: "Heat Transfer What is a heat? Heat always flows away from a hot material to a cold material Remember, heat moves in predictable ways, from a high temperature."— Presentation transcript:

1 Heat Transfer What is a heat? Heat always flows away from a hot material to a cold material Remember, heat moves in predictable ways, from a high temperature to low temperature.

2 Heat Transfer Hot objects in a cooler room will cool to room temperature. Hot objects in a cooler room will cool to room temperature. Cold objects in a warmer room will heat up to room temperature. Cold objects in a warmer room will heat up to room temperature. So that everything is in a state of equilibrium, meaning equal. So that everything is in a state of equilibrium, meaning equal.

3 Question If a cup of coffee and a red popsickle were left on the table in this room what would happen to them based on how heat moves? Why?

4 Question If a cup of coffee and a red popsickle were left on the table in this room what would happen to them based on how heat moves? Why? The cup of coffee will cool until it reaches room temperature. The popsicle will melt and then the liquid will warm to room temperature.

5 Heat Transfer Methods Heat transfers in three ways: Heat transfers in three ways: – Conduction – Convection – Radiation

6 Conduction Conduction is heat energy moving from a high- temperature object to a low-temperature object. Conduction is heat energy moving from a high- temperature object to a low-temperature object. Occurs in solids only. Occurs in solids only.

7 Conduction When you heat a metal strip at one end, the heat travels to the other end. Conduction is the direct transfer of heat or energy from one molecule to another molecule by collision.

8 In solids, every atom is bonded to another atom. If we apply heat to one part of a solid the atoms begin to vibrate.

9 Conduction The heated atoms vibrating causes atoms to collide. The heated atoms vibrating causes atoms to collide. This passes the heat from one atom to the next. This passes the heat from one atom to the next. The energy spreads throughout all the molecules of the solid, and the temperature increases. The energy spreads throughout all the molecules of the solid, and the temperature increases.

10 Conduction This is why when a metal pot or pan is placed on a hot stove, the whole pan becomes hot, rather than only the bottom.

11 Conduction examples

12 Conduction Lab If you have a metal skewer with blobs of butter on it and heat the rod, why will the blobs fall off one by one? How is this an example of conduction?

13 Convection Convection takes place when heated molecules move from one place to another, taking the heat with them. Convection is the primary way that heat moves through gases and liquids.

14 Convection

15 What happens to the particles in a liquid or a gas when you heat them? The particles spread out, rise and become less dense.

16 Fluid movement Warmer liquids and gases r___ up. Cooler liquids and gases s___. ise ink

17 Water movement Hot water rises Cooler water sinks Convection current

18 Convection Current The water or air at the bottom heats up first causing it to expand. Since the warmed air or water has a lower density (its lighter) than the air or water around it, it rises up. At the top, the air or water cools, increasing its density, which causes it to sink back down to the bottom. This up and down movement eventually heats everything. The continual cycling is called a convection current.

19 Explaining Convection Convection currents cause the movement of magma within the earth. Convection currents cause the movement of magma within the earth.

20 Why is it windy at the seaside?

21 Cold air sinks Where is the freezer compartment put in a fridge? Freezer compartment It is put at the top, because cool air sinks, so it cools the food on the way down. It is warmer at the bottom, so this warmer air rises and a convection current is set up.

22

23 Radiation

24 Radiation May Come From Other Sources Have you ever sat too close to a campfire while cooking marshmallows? Youre enjoying the warmth ….. only to notice that your skin is really warm? Have you ever sat too close to a campfire while cooking marshmallows? Youre enjoying the warmth ….. only to notice that your skin is really warm?

25 RADIATION Radiation is the transfer of energy by electromagnetic waves Radiation is the transfer of energy by electromagnetic waves Radiation does NOT require matter to transfer thermal energy Radiation does NOT require matter to transfer thermal energy Radiation = heat escaping the sun Radiation = heat escaping the sun So now we are going to cook with it! So now we are going to cook with it!


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