# Heat

## Heat is a form of energy,

We know things to be either hot or cold.

Something hot has a lot of heat energy, cold has less heat energy but it always has some.

Heat travels from warm places to cold places.

It is this transfer of heat can causes injury

This transfer of energy is how we get useful energy liberated

the following questions come from thephysicsteacher.ie

Questions to make you think

1. The foil and the cotton towel are both at the same temperature – so why does the foil feel colder?

2. A candle needs oxygen to burn, which is why if we want to resuscitate a dying fire we blow on it.

So why does blowing on a candle put it out?

3. Why does it get colder as you climb up a mountain, even though you’re getting closer to the sun?

4. When pouring boiling water into a glass, it is advised to first place a metal spoon in the glass. Why?

5. Why might a glass crack when you pour boiling water into it?

6. If you lick a frozen pipe why will your tongue stick to the pipe?

7. Why are ice cubes much better at cooling a drink that the equal amount of iced water?

8. Why is a scald from steam much more serious that a burn from boiling water?

9. Why do hurricanes pick up energy when they pass over oceans?

10. Why does a glass beaker often crack when you pour in boiling water?

11. How come a shiny material is both a bad absorber of heat and a bad radiator of heat?

12. When stepping out of bed on a cold morning, why does it feel colder if your feet touch say, a marble floor rather than a floor with carpet even though both are at the same temperature?

13. Why do footpaths/ rail-tracks/ bridges have gaps in them (hint: sometimes you see the gaps in footpaths or roads filled with a piece of rubber)?

14. Why does water rise when heated?

15. How does perspiration (sweating) help to keep us cool?

16. Many Arabs wear dark clothing in warm weather, even though dark clothes are better at absorbing heat than white clothes. Any idea why?

17. Heat can be transferred by conduction, convection or radiation. A thermos flask tries to keep hot liquids hot by preventing heat loss. Any idea how it minimises each of these three methods of heat transfer?

18. When cooking potatoes on a gas cooker you put the gas supply onto ‘max’ to boil the water as quickly as possible.

The water is now boiling.

If you turn the gas down will it take longer for the potatoes to cook or will it not make any difference?

1. Concept of temperature

## Temperature

2. Thermometric properties

3. Thermometers

## Thermometers

Concept of heat

Heat as a form of energy that causes a rise in temperature when added or a fall in temperature when withdrawn.

The difference between Temperature and Heat

Temperature is the average Kinetic Energy of the particles within a body.

Heat is the sum of the energies in a body.

Thus as the amount of heat in a body increases so too does the temperature, but if two bodies have the same temperature it cannot be said that they have the same heat.

http://id.mind.net/~zona/mstm/physics/mechanics/energy/heatAndTemperature/heatAndTemperature.html

QUANTITY OF HEAT

Quanitity of heat

1. Heat capacity, specific heat capacity

## shc

2. Latent heat, specific latent heat

## Latent heat

Using the data that follow, how much energy would be required to change 200g of ice @ -50oC to steam @ 120oC (assume standard temperature & pressure)

C(ice) = 2090 J/kg K

C(water) = 4180 J/kg K

C(steam) = 1865 J/kg K

L(fusion) = 334,000 J/kg

L(vaporisation) = 2,230,000 J/kg

HEAT TRANSFER

## How does Heat move?

It can move in 3 different ways

A car radiator is a good example of heat transfer!

Conduction convection and even a little radiation

Heat problems

Draw a diagram

Place the hot object on one side

Place the cold object on the other side

Write in all the values

Draw a line

write out an increasing energy equation

write out an decreasing energy equation

allow them to equal and solve.

HEAT: Experiments

here

Heat crossword to do

http://www.sei.ie/Schools/Secondary_Schools/Subjects/Physics/Unit_6_-_Heat_Transfer/Heat_Crossword/

The Carnot Cycle as put to you by Micheal Fowler

# Heat Engines: the Carnot Cycle

http://galileo.phys.virginia.edu/classes/152.mf1i.spring02/CarnotEngine.htm

And also by Fowler is this applet about the carnot cycle

http://galileoandeinstein.physics.virginia.edu/more_stuff/flashlets/carnot.htm

• To demonstrate the concept of supercooling in physics classes. Melted sodium thiosulfate is very easy to overcool to room temperature and when crystallization is forced, the sudden temperature jump to 48.3°C can be experienced by touch.