2. Atomic Motion
The macroscopic properties of a system are based
on the microscopic behavior of atoms.
Macroscopic Microscopic
equation of state: laws of motion:
pressure, position,
volume, velocity,
temperature energy
3. Ideal Gas Energy
Kinetic theory supplies the
energy for an ideal gas.
• Kav = (3/2)kT
Convert this to the total
system energy.
• U = (3/2)NkT
• U = (3/2)nRT
Energy based on
temperature and
This energy is internal to the
number of molecules
gas.
4. Internal Energy
The kinetic energy of an
ideal gas is its internal
energy.
• Also called thermal energy
vCM
Internal energy does not
include energy from external
measures.
• Center of mass translation
• Rigid body rotation
Fext • Potential from external force
5. Vibrations
Mean particle speed is not
the only source of internal
Rotation
energy.
around center
of mass Real molecules can have
internal motion.
• Rotation
• Vibration
These effects add to internal
energy.
Vibration at
center of mass
6. Energy Transfer
Thermal energy changes in
a system.
• It flows in and out
• Due to changes in
macroscopic properties
Heat flow
When it is due to
temperature changes it is
called heat.
7. Heat and Work
Work is a process that Heat is a process that
represents the change in the represents the change in the
mechanical energy. thermal energy.
• Force acting through a • Due to a difference in
distance temperature
• Measured in joules like • Measured in joules like
energy energy
8. Mechanical Equivalent
In the 1800’s James Joule
demonstrated that
mechanical work could
cause a change in
temperature.
Heat, like work, represented
a change in energy.
9. Calorie
Heat was measured by a Since SI has a unit of energy
change in temperature. (J) it remains the unit for all
• 1 calorie (cal) is the amount forms of energy.
of heat needed to raise 1 g • Work
of water by 1 °C. • Mechanical energy
• 1 kcal = 1000 cal, and is • Potential energy
what we call a “Calorie” for
• Dissipative energy
food.
• Heat
• Thermal energy
Calories (or kcal) are often • Internal energy
used to measure heat or
internal energy.
1 cal = 4.186 J
10. Burn It
You gobble too much ice Convert to joules from kcal.
cream and decide to walk up • W = (500 kcal)(1000
stairs to burn the additional cal/kcal)(4.186 J/cal)
500 Calories. • W = 2.1 x 106 J.
If your mass is 60 kg, what Work climbing is W = mgh.
vertical height must you • h = W / mg = (2.1 x 106 J) /
climb? (60 kg)(9.8 m/s2)
• h = 3600 m.
Real humans are inefficient
and h is closer to 700 m.
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