2. Energy that flows from something warm to
something cooler
A hotter substance gives KE to a cooler one
Heat is the transfer of energy between two objects
due to temperature differences
Heat is measured in Joules (J) because it is a form
of energy
Heat
3. Heat
The name of the transfer process is heat. What gets
transferred is energy.
Heat is NOT a substance although it is very
convenient to think of it that way.
In fact, it used to be thought that heat was a
substance.
There is a circular nature to the definitions used:
(a) energy does work or produces heat, but
(b) heat is a transfer of energy.
4. Temperature
Temperature is the property which determines the
direction heat will flow when two objects are
brought into contact
Based on the motion of the particles in a
substance
Fast motion = high temperature
Slower motion = lower temperature
Relatively describes how the particles collide with
the surface of the thermometer
Collisions transfer energy
5. Temperature Scales
Fahrenheit
Common in the US
Freezing point of water is 32ºF
Boiling point of water is 212ºF
Celsius
Common in the rest of the world (SI)
Freezing point of water is 0ºC
Boiling point of water is 100ºC
Kelvin
Used for science
Freezing point of water is 273K
Boiling point of water is 373K
6. Temperature and the Phases
of Matter
In the Fahrenheit scale, water freezes at 32
degrees and boils at 212 degrees
The Celsius scale divides the difference between
the freezing and boiling points of water into 100
degrees (instead of 180).
7. Temperature and the Phases
of Matter
All thermometers are based
on some physical property
(such as color or volume)
that changes with
temperature.
A thermometer is a device
that changes its electrical
resistance as the
temperature changes.
A thermocouple is another
electrical sensor that
measures temperature.
8. Heat and Thermal Energy
Temperature is NOT the same as thermal energy.
Thermal energy is energy stored in materials
because of differences in temperature.
The thermal energy of an object is the total
amount of random kinetic energy for all the atoms
in the object.
Remember, temperature measures the random
kinetic energy of each atom.
9. Heat and Thermal Energy
Imagine heating a cup of
coffee to a temperature of
100°C.
Next think about heating
up 1,000 cups of coffee to
100°C.
The final temperature is
the same in both cases but
the amount of energy
needed is very different.
10. First Law of Thermodynamics
Energy loss is equal to energy gain.
12. Energy and Heat flow
There Energy, in the process we call heat or heat flow,
is constantly flowing into and out of all objects,
including living objects.
Heat flow moves energy from a higher temperature to
a lower temperature.
The bigger the difference in temperature between two
objects, the faster heat flows between them.
When temperatures are the same there is no change in
energy due to heat flow.
Radiation and Conduction are the two methods of heat
transfer. Convection is a special type of conduction.
Heat has the units of energy; heat flow has the units of
power.
13. Heat flow is energy moving. It has the same units as
power - energy per unit time .
It means that during the given amount of time, during
which heat is flowing, a certain amount of energy is
transferred or moved from one place to another place
Energy and Heat flow
14. Three easy things to know about the way heat flows:
1) There has to be a temperature difference. Energy
only flows as heat if there is a temperature difference.
2) Energy as heat flows from a higher temperature to a
lower temperature.
3) The greater or larger the difference in temperature,
the faster the energy flows.
Heat flow
15. The science of how heat flows is called heat transfer.
There are three ways heat transfer works:
conduction, convection, and radiation.
Heat flow depends on the temperature difference.
Heat flow
17. Heat Conduction
Conduction occurs when two object at
different temperatures are in contact
with each other.
Heat flows from the warmer to the
cooler object until they are both at the
same temperature.
Conduction is the movement of heat
through a substance by the collision of
molecules. At the place where the two
object touch, the faster-moving molecules
of the warmer object collide with the
slower moving molecules of the cooler
object.
18. Heat Conduction
Conduction is the transfer of heat through materials
by the direct contact of matter.
Dense metals like copper and aluminum are very
good thermal conductors.
A thermal insulator is a material that conducts heat
poorly.
19. Thermal Conductivity
The thermal conductivity of a material describes
how well the material conducts heat.
20. Heat Conduction Equation
PH = k A (T2 -T1)
L
Area of cross section (m2)
Length (m)
Thermal conductivity
(watts/moC)
Heat flow
(watts)
Temperature
difference (oC)
21. Convection
Convection is the transfer of
heat by the motion of liquids
and gases.
– Convection in a gas occurs
because gas expands when
heated.
– Convection occurs because
currents flow when hot gas rises
and cool gas sink.
– Convection in liquids also
occurs because of differences in
density.
22. Convection
When the flow of gas or
liquid comes from
differences in density and
temperature, it is called
free convection.
When the flow of gas or
liquid is circulated by
pumps or fans it is called
forced convection.
24. Convection
Convection depends on speed and surface area.
Motion increases heat transfer by convection in all
fluids.
If the surface contacting the fluid is increased, the rate
of heat transfer also increases.
25. Convection and Sea
Breezes
On a smaller scale near
coastlines, convection is
responsible for sea breezes.
During the daytime, land is
much hotter than the ocean.
A sea breeze is created when
hot air over the land rises due
to convection and is replaced
by cooler air from the ocean.
At night the temperature
reverses so a land breeze
occurs.
26. Heat Convection Equation
PH = h A (T2 -T1)
Area contacting fluids (m2)Heat transfer coefficient
(watts/m2oC)
Heat flow
(watts)
Temperature
difference (oC)
27. Radiation
Radiation is heat transfer by
electromagnetic waves.
Thermal radiation is
electromagnetic waves
(including light) produced by
objects because of their
temperature.
The higher the temperature
of an object, the more
thermal radiation it gives off.
28. • Radiation
Radiation
Heat from the sun is the
best example of radiation.
The sun is rays reach the
earth without having any
material medium in
between the earth and the
sun.
The electromagnetic rays
carry energy from the sun is
surface to the earth and
heat up the earth and its
atmosphere.
29. Radiant Heat
We do not see the thermal
radiation because it occurs
at infrared wavelengths
invisible to the human eye.
Objects glow different colors
at different temperatures.
30. The graph of power versus wavelength for a perfect
blackbody is called the blackbody spectrum.
Radiant Heat
A perfect blackbody is a surface that reflects nothing
and emits pure thermal radiation.
31. Radiant Heat
The total power emitted as thermal radiation by a
blackbody depends on temperature (T) and surface
area (A).
Real surfaces usually emit less than the blackbody
power, typically between 10 and 90 percent.
The Kelvin temperature scale is used in the Stefan-
Boltzmann formula because thermal radiation
depends on the temperature above absolute zero.
32. Stefan-Boltzmann
formula
P = s AT4
Surface area (m2)
Stefan-Boltzmann constant
5.67 x 10-8 watts/m2K4)
Power
(watts)
Absolute temperature
(K)
