Flow of thermal energy

1. Heat
The flow of thermal
energy from one
object to another.
Heat always flows
from warmer to
cooler objects.
Ice gets warmer
while hand gets
cooler
Cup gets cooler while
hand gets warmer

2. Imagine…Imagine…
A hot day in your back yard is aA hot day in your back yard is a
Piece of SteelPiece of Steel and aand a wood Blockwood Block..
Would you want to stick your hand to theWould you want to stick your hand to the
wood or touch the steel?wood or touch the steel?
SteelSteelSteelSteel WoodWood
You would want to touch the wood becauseYou would want to touch the wood because

3. Things heat up or cool down at different rates.
Land heats up and cools down faster than
water,
This is why land heats up
quickly during the day and
cools quickly at night and
why water takes longer

4. Thermal (heat) capacity
What requires more
energy to heat up by
1o
C?
Different material heat up at different rate
Different material store different
amount of heat energy!!!

5. Heat Capacity
The quantity of heat required to
raise the temperature of any mass
of a substance by one degree
Celsius (or Kelvin)
The unit is (J/ o
C)

6. Equation:
q = C x ΔT
• q = heat transferred (in joules)
• C = specific heat capacity
• ΔT = change in temperature
ΔT = Tfinal - Tinitial

7. Thermal (heat) capacity
What requires more
energy to heat up by
1o
C?
1 kg water 1 kg aluminium1 kg aluminium
4200 joules of
energy
900 joules of
energy
Water must be
supplied with
nearly five times
as much energy as
aluminium for the
same rise in
temperature.
It’s all to do with the SPECIFIC HEAT CAPACITY of the material

8. You will possibly have
noticed that it is easier to
warm up
a saucepan full of oil
than it is to warm up
one full of water.
Specific Heat Capacity can be thought of
as a measure of how much heat energy
is needed to warm the substance up.

9. Things heat up or cool down at different rates.
Land heats up and cools down faster than
water,
C water = 4184 J / kg C (“holds” its heat)
C sand = 664 J / kg C (less E to change)
This is why land heats up
quickly during the day and
cools quickly at night and
why water takes longer

10. Specific Heat Capacity
The quantity of heat required to
raise the temperature of 1 kilo
gram of a substance by one
degree Celsius (or Kelvin)
The unit is (J/kg o
C)

11. Equation:
q = m x C x ΔT
• q = heat transferred (in joules)
• m = mass (in Kilo grams)
• C = specific heat capacity
• ΔT = change in temperature
ΔT = Tfinal - Tinitial

12. • The next table shows how much energy it
takes to heat up some different substances.
• The small values show that not a lot ofThe small values show that not a lot of
energy is needed to produce aenergy is needed to produce a
temperature change, whereas the largetemperature change, whereas the large
values indicate a lot more energy isvalues indicate a lot more energy is
needed.needed.

13. • Approximate values in J / kg °C of the Specific
Heat Capacities of some substances are:
Air 1000 Lead 125
Aluminium 900 Mercury 14
Asbestos 840 Nylon 1700
Brass 400 Paraffin 2100
Brick 750 Platinum 135
Concrete 3300 Polythene 2200
Cork 2000 Copper 390
Glass 600 Rubber 1600
Gold 130 Silver 235
Ice 2100 Steel 450
Iron 500 Water 4200

14. An example of a calculation using the
specific heat capacity equation:
How much energy would be needed to heat
450 grams of copper metal from a
temperature of 25.0 ºC to a temperature of
75.0ºC?
(The specific heat of copper is 385 J/Kg ºC.)