Transcript Understanding Heat Transfer, Conduction, Convection and

Question
 If a cup of coffee and an ice cream cone were left on
the table in this room what would happen to them?
Why?
 The cup of coffee will cool until it reaches room
temperature. The ice cone will melt and then the
liquid will cool to room temperature.
What is Heat?
This is the movement of thermal
energy from a substance at a
higher temperature to another at a
lower temperature.
Heat vs. Temperature
Heat is the actual energy…
Temperature is the measure of average
kinetic energy of particles in a
substance.
Heat is NOT Temperature
Heat Transfer
 Heat always moves from a warmer place to a
cooler place.
 Hot objects in a cooler room will cool to room
temperature.
 Cold objects in a warmer room will heat up to
room temperature.
Heat Transfer Methods
 Heat transfers in three ways:
Conduction
Convection
Radiation
Conduction
Conduction heat transfer is the flowing of heat
energy from a high-temperature object to a
lower-temperature object. Must have contact
(touch)
EXAMPLE OF CONDUCTION
 A piece of cheese melts as heat is transferred from the
meat to the cheese (Contact)
Have you ever…
 Touched a metal spoon sitting in a pan of boiling
water only to be surprised by HOW hot it is??
Think back to what you know about metals and
nonmetals. What conducts heat better, metal or
nonmetal? Why?
Conduction
When you heat a metal strip at one end, the heat
travels to the other end.
As you heat the metal, the particles vibrate, these
vibrations make the adjacent particles vibrate, and so on
and so on, the vibrations are passed along the metal and
so is the heat. We call this? Conduction
Metals are different
The outer e______
lectrons of metal atoms
drift, and are free to move.
When the metal is
heated, this ‘sea of
inetic
electrons’ gain k_____
energy and transfer it
throughout the metal.
Insulators, such as w___
ood and p____,
lastic do not
have this ‘sea of electrons’ which is why they
do not conduct heat as well as metals.
Why does metal feel colder than wood, if they
are both at the same temperature?
Metal is a conductor, wood is an insulator. Metal
conducts the heat away from your hands. Wood
does not conduct the heat away from your hands as
well as the metal, so the wood feels warmer than
the metal.
Convection
Convection takes place when heated molecules move
from one place to another, taking the heat with them.
Convection is common in both the atmosphere, as
well as in the oceans. Convection = VENTS
Convection is the primary way that heat moves
through gases and liquids.
Convection
CONVECTION
• Convection is the movement that transfers heat within
fluids and air (gas)
• Heat is transferred by currents within the fluid or gas
• Convection = VENTS (through air and liquid particles)
• Convection moves in
a circular pattern
Examples of Convection:
 Have you ever noticed that the air near the ceiling is
warmer than the air near the floor? Or that water in
a pool is cooler at the deep end?
 Examples: air movement in a home, pot of heating
water.
Convection
What happens to the particles in a liquid or a
gas when you heat them?
The particles spread out and
become less dense.
Water movement
Cools at the
surface
Cooler
water sinks
Convection
current
Hot water
rises
Cold air sinks
Where is the
freezer
compartment
put in a fridge?
It is put at the
top, because
cool air sinks,
so it cools the
food on the
way down.
Freezer
compartment
It is warmer
at the
bottom, so
this warmer
air rises and
a convection
current is
set up.
Why is it windy at the seaside?
Radiation
The third method of heat transfer
How does heat energy get
from the Sun to the Earth?
?
There are no particles
between the Sun and the
Earth so it CANNOT
travel by conduction or
by convection.
RADIATION
RADIATION
 Radiation is the transfer of energy by electromagnetic
waves
 Radiation does NOT require matter to transfer thermal
energy
 Radiation = Radiates (heat escaping the sun)
Examples of RADIATION
1. Fire
2. Heat Lamps
3. Sun
Radiation
Radiation travels in straight lines
True/False
Radiation requires particles to travel
True/False
Radiation travels at the speed of light
True/False
Radiation
 The transfer of energy by electromagnetic waves.
Examples:
 Sun
 Fire
 Light bulb
Radiation question
Why are houses painted white in hot countries?
White reflects heat radiation and keeps the house cooler.
Example of
water being heated.
 The fast-moving particles of the Conduction
 Think of a metal spoon in a pot of
fire collide with the slow-moving
particles of the cool pot.
 Because of these collisions, the
slower particles move faster and
heat is transferred.
 Then the particles of the pot
collide with the particles in the
water, which collide with the
particles at one end of the spoon.
 As the particles move faster, the
metal spoon gets hotter. This
process of conduction is repeated
all along the metal until the entire
spoon is hot.
http://www.youtube.com/watch?
v=wz6wzOtv6rs
1.
Which of the following is not a
method of heat transfer?
A.
Radiation
B.
Insulation
C.
Conduction
D.
Convection
2. In which of the following are
the particles closest together?
A.
Solid
B.
Liquid
C.
Gas
D.
Fluid
3. How does heat energy reach
the Earth from the Sun?
A.
Radiation
B.
Conduction
C.
Convection
D.
Insulation
4. Which is the best surface for
reflecting heat radiation?
A.
Shiny white
B.
Dull white
C.
Shiny black
D.
Dull black
5. Which is the best surface for
absorbing heat radiation?
A.
Shiny white
B.
Dull white
C.
Shiny black
D.
Dull black
3 Ways Energy (Heat) is Transferred
*Transferred in
rays or waves
*Energy from the
Sun warms the
Earth
*Transfer of heat (energy)
that happens when
molecules bump into
each other
*Objects must be
touching
*”Conduction is touchin’”
*Transfer of heat by the flow
of material
*In warm air, the molecules
move apart, so it is less
dense and rises
*In cooler air, the molecules
move closer together, so it is
more dense and sinks
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http://www1.teachertube.com/view
Video.php?video_id=159713