1. Temperature:
• Recall that temperature is a representation of how
much wiggling a substance is doing.
– Can also think of as a measure of average energy of
motion.
• When we strike a coin with a hammer it will become
warm.
• When we put a flame to a liquid it will become
warmer.
• When we compress air it will become warmer.
2. Absolute Zero
• The point where mean energy is zero.
• The temperature where an ideal gas would have no
volume.
• Measuring on this scale, doubling of temperature is a
doubling of mean energy.
3. Heat
• Heat always flows from warmer to colder.
• Heat is the flow of thermal energy.
• Thermal energy is a property of an object.
• Heat is measured in calories
1 calorie = 4.28 joules
• Food is measured in Calories.
1 Calorie = 1000 calories
5. Demonstration: hot/cold and human
perception
• Place one hand in the ‘hot’
container.
• Place other hand in the ‘cold’
container.
• After a minute or so, place
both hands in the ‘warm’
container.
• Do your hands report
different temperatures for
the warm container? Hot Warm Cold
Hot Warm Cold
6. The Kelvin Temperature scale
• Starts at absolute zero (0 K or –273ºC); as cold as it can
get.
• Each degree is the same size as a Celsius degree
• Ice melts at 273 K
• Water boils at 373 K
What does absolute zero mean?
• Mean energy of the substance is zero.
7. How the distribution of molecular energies
changes with temperature
from www.gs68.de/tutorials/ plasma/node7.html
Fractionofatomsinthe
sample
Energy of the atoms
8. Specific Heat Capcity
• Measured in Joules per
gram-Kelvin or Joules per
gram-Celsius.
• To calculate heat required to
change temperature:
– Heat = c*m*ΔT
• Water has a high heat
capacity. This has wonderful
effects on our climate.
9. Example Problem
• The specific heat capacity of copper is more than
twice that of silver. This means that if we had 1-kg of
copper and 1-kg of silver, and each started at the
same temperature and each received 1000 Joules of
energy, then
a) the copper would end up hotter than the silver
b) the silver would end up hotter than the copper
c) both pieces of metal would end up having the same
increase in temperature
10. Heat
• Heat always moves from warmer to cooler.
• All objects radiate energy
– if energy radiated is less than absorbed, object heats up
– If energy radiated is more than absorbed, object cools off
– If energy radiated is equal to that absorbed the object is at thermal
equilibrium (as all things at room temperature are).
Heating Up Cooling Off Equilibrium
11. Sample Problem
• The picture to the left
represents an object doing
what? (heating, cooling,
equilibrium.)
• Why?
Heating. It is receiving more energy than it is radiating.
12. Heat is a transfer of thermal energy
• All objects contain thermal energy.
– Energy contained is proportional to temperature
– Energy is also proportional to ‘size’ of material
13. • Why is it that something like a speck of hot
water or oil kicked out of a pan will rarely burn
you?
– While it is much hotter, it is very small and contains
little thermal energy.
14. What is cold?
What is dark?
• The absence of light.
Cold is similar – cold is not something you have,
it is something you lack: thermal energy.
17. • During this odd state of
water there are small
domains within the liquid
that still have the very
open, ordered solid
structure.
• The decrease in density
is caused by these
“melting”.
18. First Law
Most simply stated: Energy can neither be created nor
destroyed. It can only change forms.
So when heat (energy) flows into or out of a system,
the gain or loss of thermal energy equals the amount
of heat transferred.
19. Second Law
Heat never spontaneously flows from a cold
substance to a hot substance.
Though we can force this to happen by putting
work into the system.
Consider your refrigerator or air-conditioner.
20. Third Law
No system can reach absolute zero.
Losses must always occur because we cannot pull
all the energy out of a system.
No perpetual motion machines. In a sense, no
“free energy.”
21. Conduction
• Hot stuff vibrates more.
• Something vibrating less in contact with this will gain
energy through the collisions.
– No material moves from one block to the other!
– Only the thermal energy moves.
Quickly
moving
stuff
Hits slowly
moving
stuff
Over time, all comes to
equilibrium
22. Conduction 2
• Some objects feel warm,
others cool. Why? They
are both room
temperature...
– Conduction of heat.
– Metals are good
conductors, their
electrons move easily
which helps them also be
good heat conductors.
23. Conduction 3
• Air is a poor conductor of heat.
– So, things that trap air in small pockets are very
good insulators.
• Fiberglass insulation
• Foam
• Aerogels
• Insulators do not stop the conduction of heat,
they just slow the speed at which it moves.
24. Convection
• How it works:
– Stuff warms up
– Warm stuff expands, making it lower in density
– Low density stuff floats on high density stuff so warm stuff rises
– Cool stuff moves in to the space left by rising warm stuff
– Warm stuff cools, shrinks and falls
– Repeat
• Unlike Conduction, Stuff Moves.
25. Radiation
• All objects radiate
electromagnetic waves
– Infrared, usually at room
temperature
– visible light when rather hot
• These electro-magnetic
waves carry with them
energy.
• Other objects can absorb
this energy and warm up.
Image courtesy Fir0002/Flagstaffotos
GNUFDL v1.2
26. Blackbody Radiation
• Frequencies of light
emitted depend on
temperature.
– Hotter objects, higher
frequency.
– Cooler objects, lower
frequency.
• We actively emit in the
infrared. We also absorb
some colors while reflecting
others.
27. • Objects always emit radiation based on
temperature.
• Objects absorb some colors and reflect others
(this is responsible for the color we observe an
object to be).
– Black absorbs most visible frequencies
– White reflects most
– Demonstration!
