Download Thermal Energy

Thermal Energy
Warm Up:
• To shape metal into a horseshoe, the metal is
heated in a fire. Why will a horseshoe bend
when it’s very hot, but not after it cools?
What was different ?
• There was
more motion in
the hot water
• The energy of
motion is Kinetic
Energy
• Matter is
always in
motion
• Particles of
gases,
liquids, and
solids all
move
Heat
• Heat is the transfer of thermal energy from
one object to another because of a
temperature difference.
• Heat flows spontaneously from hot objects
to cold objects.
Heat
Heat is related to
temperature:
The Temperature of
an object is the
measurement of the
average kinetic energy
(KE) of particles
• As an object heats up its particles move
__________________ on average. As a
result, the average kinetic energy (and the
temperature) _________________.
• Number of collisions between particles
increases…. Thermal energy is
transferred from hot to cold objects.
What do Temperature Scales
Measure?
• Fahrenheit: used in US
• Celsius: used in other countries
• Kelvin: SI unit
0 K = -273°C
0°C = 273 K
Thermal Energy
• Thermal Energy (Q) is the sum of the
kinetic energy + the potential energy of all
the particles in an object:
Q = KE + PE
• Thermal energy depends on the mass,
temperature and phase (solid, liquid, or
gas) of an object.
Thermodynamics
• First Law of
Thermodynamics:
the increase in
thermal energy of a
system equals the
work done on the
system plus the heat
transferred to the
system
–Energy is
CONSERVED
Open Systems
• In an open system, heat flows across the
boundary, or work is done across the
boundary.
• What are examples of open systems?
Closed Systems
• In a closed system, no heat flows across
the boundary and no work is done across
the boundary.
• What are examples of closed systems?
Thermodynamics
• Second Law of
Thermodynamics:
Heat flows from
warmer objects to
cooler objects
Heat cannot flow from
a cooler object to a
warmer object unless
work is done
How do solids transfer heat?
• Conduction: the
transfer of thermal
energy by collisions
between particles in
matter.
• Particles in solids
vibrate and collide
with each other
• List 3 examples
of conduction
Convection
• Convection is the
transfer of thermal
energy in a gas or
liquid by the
movement of warmer
and cooler fluid from
place to place.
Knowing this, what will happen to a piece of ice floating at the top of a
warm glass of water?
What will happen to a piece of ice at the bottom of a glass of water?
• List 3 examples of convection
Radiation
• Radiation is the transfer of
energy by electromagnetic
waves. These waves
travel in the empty spaces
between particles until their
energy is absorbed by a
particle.
• Would radiation pass
through a solid or a gas
more easily?
• List 3 examples
of heat radiation.
Heat
• Heat is the thermal
energy that is
transferred from
particles at a higher
temperature to
particles at a lower
temperature
Can you control heat flow?
• An INSULATOR is a material in
which heat flows slowly
• Good Insulators: plastic, wood, air,
fiberglass
• Materials that aren’t good insulators
are CONDUCTORS. Heat flows
quickly through a conductor.
• Good Conductors:
metals
What if there is no material?
• There is no
conduction if there is
no matter. A vacuum
(empty space) is a
perfect insulator
because very little
heat transfer can take
place.
• We use vacuum insulators and air insulators all
the time. List some examples.
How is the water inside being
heated?