Transcript Temperature, Heat & Expansion

Temperature, Heat
&
Expansion

Temperature - The quantity that tells how
hot or cold something is compared with a
standard.
Measuring temperature:
A common thermometer measures
temperature by showing the expansion &
contraction of a liquid in a glass tube using
a scale.
*the liquid is usually mercury or colored
alcohol

Temperature Scales

-
Celsius
most widely used scale
international scale
00c = temperature at which water freezes
1000c = temperature at which water boils

Fahrenheit
-
used commonly in the U.S.
32o = temperature at which water freezes
212o = temperature at which water boils
-

-
Kelvin
used in scientific research
degrees are the same as Celsius and are called “Kelvin”
0oK = absolute zero (0oK = -273oC)
**Absolute zero is the temperature at which a substance has NO kinetic
energy.

Temperature is proportional to the average
kinetic energy.
As temperature increases – kinetic energy
increases.
Heat

Heat – the energy that transfers from one object
to another because of a temperature difference.
**HEAT IS ENERGY**

Heat is energy “in transit” from a body of higher
temperature to one of lower temperature

The energy resulting from heat flow in Thermal
energy.
Thermal Equilibrium
What is thermal equilibrium???
 When objects in thermal contact with each
other reach the same temperature and no
heat flows between them.
ex:
to read a thermometer we wait until the liquid stops
moving. This is the point when the liquid in the
thermometer and the substance being measured have
reached thermal equilibrium.
Internal Energy
The grand total of all energies in a substance is
the internal energy.
A substance does not contain HEAT, it contains
ENERGY !!!
This includes:
The KE of moving molecules and atoms of a substance.
The PE due to the forces between molecules or atoms.
Measuring Heat

Heat is measured in calories.

A calorie = the amount of heat required to raise
the temp. of 1g water, 1oC.
A kilocalorie = 1000 calories

Kilocalories are the heat unit used in rating
foods. Kilocalories are often referred to as
Calories. (with a capitol “C”)
Specific Heat Capacity

Specific heat is the quantity of heat required to
raise the temp. of a unit of mass of a substance
by 1 degree.

Different substances have different capacities for
storing internal energy
(re: ability to “hold heat”)
and
require specific quantities of heat to raise the
temp. of a given mass a specific number of
degrees.
Example:


1g of water requires 1 calorie to raise the temp. 1oC.
WHILE
1g of iron requires 1/8 as much energy to raise the
temp. 1oC.
Water absorbs more heat per gram that iron for the same
temperature change.
So… water has a higher Specific Heat.
(BTW – water is considered to have a very high sp.heat)
Thermal Expansion
When the temp. of a substance increases the
molecules move faster (increase KE)
This results in the EXPANSION of the substance.
With few exceptions – all forms of matter (solid,
liquid & gas) expand when heated
and
contract when cooled.
Heat Transfer
Conduction
Conduction = heat transfer within and
between different materials in direct
contact. (molecule to molecule)
conductor – material that conducts heat
well (metal)
insulator – material that delays the
transfer of heat (wood)

Poor conductors = good insulators
 Good conductors = poor insulators

Which feels colder: barefeet on tile or carpet?
The tile – because it is a good insulator. The heat
moves from your feet to the tile.
Does a blanket make you feel warmer?
The blanket is a good insulator and delays the
transfer of heat from your body to the air.
Convection
Convection is when heat is transfer
through a current in a fluid.
** fluids can be either liquids or gases
examples:
- Air in contact with a hot stove rises and
warms the region above.
- Water boils through convection
- convection currents stir our atmosphere

Radiation

Radiation is the transfer of heat through
electromagnetic waves. (UV light, visible light,
infrared, microwaves, radio waves, etc.)
Examples:
- The sun
- a lightbulb
- a fireplace
Any energy, including heat, that is transmitted by
radiation is called radiant energy.