Download 16.2 Heat and Thermodynamics

16.2 Heat and Thermodynamics
16.2 Heat and Thermodynamics
Key Concepts
• Why is conduction slower in gases than in liquids or
solids?
• In what natural cycles do convection currents occur?
• How does an object’s temperature affect radiation?
• What are the three laws of thermodynamics?
16.2 Heat and Thermodynamics
Conduction
Conduction is the transfer of thermal energy with
no overall transfer of matter.
____
– occurs within a material or between materials
that are ___________________
touching
collisions
– due to the ______________
between particles
Newton’s cradle shows how
kinetic energy is transferred
through the collisions of the balls
16.2 Heat and Thermodynamics
Conduction
slower
Conduction in gases is ____________
than in
liquids and solids because the particles in a gas
are ______________
apart, making them
farther
collide _______
often.
less
16.2 Heat and Thermodynamics
Thermal Conductors
A thermal conductor is a material that conducts thermal
well
energy ________.
good
Metals are __________
thermal conductors.
The bottom of this
metal frying pan
first
heats up ________
and the handle
________
last
16.2 Heat and Thermodynamics
Conduction
better
Tile is a ____________
conductor than wood.
A tile floor feels ____________
than a wooden
colder
floor when you walk on it because the tile
________________
thermal energy more rapidly
transfers
away from your skin.
Heat flows from warm objects
to cold objects
Warmer foot  colder tile
16.2 Heat and Thermodynamics
A material that conducts thermal energy poorly is called a
thermal ____________________.
insulator
Air
________
is a very good insulator.
trapped air to slow down
Examples: Foam cups use ___________
conduction...so do wool sweaters
16.2 Heat and Thermodynamics
Convection
Convection is the transfer of thermal energy when particles
of a fluid __________
move from one place to another.
Quick Review…what states of matter are considered fluids?
Liquids and gases
Convection currents are important in many natural cycles,
such as…
• ocean _____________
currents
weather
• _____________
systems
hot _______
rock in Earth’s interior
• movements of ______
16.2 Heat and Thermodynamics
Convection
Passing sandbags along a line is like
A. ______________
transferring thermal energy by convection.
air
B. The arrows show convection of _______
in an oven.
16.2 Heat and Thermodynamics
Convection
current
A convection _____________
occurs when a fluid
circulates in a __________
as it alternately heats
loop
up and cools down.
• Air at the bottom of an oven
heats up, expands, and becomes
less dense. The hot air
rises
____________.
• Rising hot air cools as it moves
away
_________
from the heat source.
• The cool air contracts, become
sinks
more dense, and _________
16.2 Heat and Thermodynamics
Radiation
waves
Radiation is the transfer of energy by __________
space
moving through ______________.
All objects radiate energy.
As an object’s temperature _____________,
the
increases
________
at which it radiates energy also
rate
increases.
16.2 Heat and Thermodynamics
Radiation
sun
The ______
warms you by radiation on a clear day.
Heat lamps used in restaurants are another example
of radiation.
16.2 Heat and Thermodynamics
Thermodynamics
transfers
The study of _________________
between thermal energy
and other forms of energy is called thermodynamics.
Joule
James Prescott ____________
(1818-1889) carefully
measured the energy changes in a system
falling weight
– his system included a ________
pushed a paddle wheel in a
that ________
container of water.
– Joule found that the ________
work done
by the falling weight almost exactly
thermal energy
equaled the ___________
gained by the water.
16.2 Heat and Thermodynamics
Thermodynamics
First Law of Thermodynamics
The first law of thermodynamics states that
conserved
energy is ______________.
Energy cannot be created or destroyed, but it
forms
can be converted into different ____________.
16.2 Heat and Thermodynamics
Thermodynamics
Pushing on the pump does
work
________
on the system.
Some of the work is
converted into ___________
thermal
energy, which heats the air in
the pump and the tire.
16.2 Heat and Thermodynamics
Thermodynamics
Second Law of Thermodynamics
The second law of thermodynamics states that
cold
thermal energy can flow from ___________
objects to ___________
objects only if _______
warm
work
is done on the system.
16.2 Heat and Thermodynamics
Thermodynamics
• Example A refrigerator must do work to
cold food
transfer thermal energy from the _______
warm room air.
compartment to the ________
• The thermal energy is released by _________
coils
at the bottom or in the back of the refrigerator.
16.2 Heat and Thermodynamics
Thermodynamics
heat
A heat engine is any device that converts _____
into __________
work
• Thermal energy that is not converted into work is
waste heat.
called _________
• Waste heat is transferred the ________________
surrounding
environment.
16.2 Heat and Thermodynamics
Thermodynamics
Spontaneous changes will always make a system
_______
orderly, unless work is done on the
less
system.
For example, if you walk long enough, your
shoelaces will become __________.
untied
Disorder in the universe as a whole is always
____________________.
increasing
16.2 Heat and Thermodynamics
Thermodynamics
The third law of
thermodynamics states
that absolute zero
cannot be reached.
_________
This physicist uses a laser
to cool rubidium atoms to
3 billionths of a Kelvin
above absolute zero.
16.2 Heat and Thermodynamics
Assessment Questions
1. What form of energy transfer requires the motion
of particles of a fluid?
a.
b.
c.
d.
conduction
convection
radiation
insulation
16.2 Heat and Thermodynamics
Assessment Questions
2. Thermal energy can move from a cooler object to a
warmer object when
a.
b.
c.
d.
the warmer object is larger.
the cooler object has more thermal energy.
energy is transferred by radiation.
work is done on the system.
16.2 Heat and Thermodynamics
Assessment Questions
3. According to the third law of thermodynamics, it is
impossible
a. to cool an object to absolute zero.
b. transfer thermal energy from a cooler object to a
warmer object.
c. convert energy from one form to another.
d. account for all of the energy in a system.
16.2 Heat and Thermodynamics
Assessment Questions
4. All metals are good thermal insulators.
True
False