Download EQ: How can heat be transferred from one place to another?

EQ: How can heat be transferred
from one place to another?
Temperature, Thermal Energy and Heat
Temperature
 The weather report says that
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today’s high temperature will
be 45 degrees and it will be
sunny
What should you wear?
A heavy coat?
A hoodie?
T-shirt and shorts?
Pajamas?
What you decide depends on
what 45 degrees means.
Temperature
 You don’t need anyone
telling you at this point in
your life that hot means
higher temperatures, and
cold means lower
temperatures.
 But when scientists think of
high and low temperatures,
they aren’t thinking about
the words hot and cold
 Instead, they think about
particles of matter in
motion.
Temperature
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All matter is made of tiny particles.
Particle: any one of the very small parts of
matter (such as a molecule, atom, or
electron).
These particles are always moving even if the
matter they make up is sitting still.
The energy of motion is kinetic energy.
This means that all particles of matter have
kinetic energy.
The faster the particles move, the more
kinetic energy they have.
Temperature is the measure of the average
kinetic energy of the individual particles of
matter.
The faster the particles move, the higher the
temperature
The slower the particles move, the lower the
temperature
Temperature
 Which has the higher
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temperature?
The hot cocoa or the cold
glass of chocolate milk?
Which has a greater average
kinetic energy?
What would happen to the
chocolate milk’s kinetic
energy if it is heated?
What would happen to the
hot cocoa’s kinetic energy if
several ice cubes were added?
Thermal Energy and Heat
 Different objects at the same
temperature can have
different energies.
 To understand this, you have
to understand thermal energy
and heat.
 They are not the same thing.
 Temperature, thermal energy
and heat are related, but they
are all different
Thermal Energy
 The total energy of all the
particles in an object.
 It depends on the number
of particles in an object,
the temperature of the
object(how fast the
particles are moving), and
the arrangement of the
object’s particles.
Thermal Energy
 The more particles an
object has at a given
temperature, the more
thermal energy it has.
 For example, 1 liter of hot
cocoa has more thermal
energy than a 0.2L of hot
cocoa, because the larger
pot contains more cocoa.
 https://www.youtube.co
m/watch?v=f1eAOygDP5s
Thermal Energy
 On the other hand, the
higher the temperature (or
the faster the movement of
particles) of an object, the
more thermal energy the
object has.
 For example, a 1 liter pot
of hot cocoa has more
thermal energy than 1liter
of cold chocolate milk.
Heat
 Thermal energy that is
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transferred from matter at
a higher temperature to a
lower temperature.
One misconception is that
objects contain heat.
Objects do not contain heat.
They have a temperature and
contain thermal energy.
Only when the thermal
energy from one object is
transferred to another object
is it called heat.
Heat
 Heat is thermal energy
moving from warmer
object to a cooler object.
 For example, when you
hold an ice cube in your
hand, the ice melts
because thermal energy is
transferred from your hand
to the ice cube.
Temperature, Thermal Energy, Heat
Temperature
Thermal Energy
Heat
Temperature is the measure of
the average kinetic energy of
the individual particles of
matter.
The total energy of all the
particles in an object.
Thermal energy that is
transferred from matter at a
higher temperature to a lower
temperature.
Faster movement = higher
temperature
More particles = more
Heat always transfers from the
thermal energy (more is more!) warmer object to the cooler
object
Higher temp = more thermal
energy
Specific Heat
 You run across the hot sand
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toward the water at the
beach.
But you don’t get more
than a toe in the water.
Why?
It’s too cold!
How can the sand be so hot
and the water so cold since
the sun heats them both?
Specific Heat
 The answer is that water
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requires more heat to raise its
temperature than sand does.
When an object is heated, its
temperature will rise.
But the temperature does not
rise at the same rate for all
objects.
The rate depends on the
chemical make up of the object.
To change the temperature of
different objects by the same
amount, different amounts of
heat are required.
Specific Heat
 The amount of energy required
to raise 1 kg of a material by 1
kelvin (degree) is called its
specific heat.
 A material with a very high
specific heat can absorb a great
amount of thermal energy
without a great change in
temperature.
 On the other hand, a material
with a very low specific heat
would have a large temperature
change after absorbing the same
amount of thermal energy.
EQ: How can heat be transferred
from one place to another?
Heat Transfer: Conduction, Convection and
Radiation
https://www.youtube.com/watch?v=eZkHzc-kuj4
The Transfer of Heat
 While we tend to use the words temperature, thermal
energy and heat synonymously, they do not mean the same
thing!
 Temperature is the measure of the average kinetic energy of
the individual particles of matter.
 Faster movement = higher temperature
 Thermal energy is the total energy of all the particles in an
object.
 More particles = more thermal energy (more is more!)
 Higher temp = more thermal energy
 Heat is thermal energy that is transferred from matter at a
higher temperature to a lower temperature.
How is Heat Transferred?
 There are three ways in
which heat can move:
 Conduction
 Convection
 Radiation
Conduction: Energy Transfer by Contact
 In the process of conduction, heat is
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transferred from one particle to
another through direct contact.
EX:
A cold metal spoon in a pot of
water on a hot stove
The fast moving particles in the
water collide with the slower
moving particles in the spoon.
This causes the particles in the
spoon to move faster
Heat always flows from warm to
cold
The spoon becomes hotter.
Conduction = Contouchin’
Conduction: Energy Transfer by Contact
 The other side of the pillow
 Does the pillow cool you off or
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does your body heat warm the
pillow?
Why?
Other examples:
Melting an ice cube in your
hand
Sitting on a hot fireplace mantle
Swimming on a hot summer day
How is the heat flowing?
Convection: Heat Transfer by
Movement
 Convection is heat transfer
by the movement of
currents in a fluid
 Current = moving stream
 Fluids = liquids and gases
 Air
 Water
 Currents will flow from
warm to cool.
 Direct contact between
matter is necessary
Convection: Heat Transfer by
Movement
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EX: boiling pot of water
When water at the bottom of a pot is heated,
its particles move faster (raising the
temperature) and farther apart.
As a result, the water becomes less dense.
Less dense fluids will float to the top, so the
heated water rises.
The cooler water is denser, so it drops to the
bottom.
But then the cooler water heats, and rises
And the water at the top cools, and sinks
This rising and falling of the water (or any
fluid) creates a convection current.
repeat
http://www.schooltube.com/video/679d4
fb85386811734a7/
Convection: Heat Transfer by
Movement
 Other examples of
convection:
 Wind (uneven heating
warm vs. cold air)
 Magma moving the Earth’s
tectonic plates
 Ocean currents
 Warm-water: flow from
equator to poles
 Cold-water: flow from
poles to equator
Radiation: Heat Transfer by Waves
 Radiation is heat transfer
by electromagnetic waves
 No direct contact is needed
 EX:
 You can feel radiational
heating from a fire in a
fireplace from across the
room.
Radiation: Heat Transfer by Waves
 Other examples of
radiational heat transfer
are:
 The Sun’s energy heating
our atmosphere (and your
driveway/pool deck!)
 Laying out in the sun to get
a tan
Heat Moves ONE Way
 If two objects have different
temperatures, heat will always
flow from the warmer object to
the cooler object.
 When heat flows into matter,
more particles are heated, and
the thermal energy rises.
 As the thermal energy rises, the
particles start moving faster, so
the temperature rises.
 Heat will flow from one object
to the other until the two
objects have the same
temperature.
Heat Moves ONE Way
 EX:
 Hot food sitting out cools to room
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temperature if not eaten quickly.
BUT!!!
Did the food cool or did the
surrounding air warm?
Why?
In science, there is no such thing as
coldness.
Instead, the matter grows colder as
thermal energy flows from it and
transfers to another object/form of
matter.
Heat transfer occurs only in one
direction.
Conductors and Insulators
 Have you ever stepped from a
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rug onto a tile floor?
The tile floor feels cooler.
But if you measured their
temperatures, they would be
the same (room temperature)
The difference between them
has to do with how materials
conduct heat.
A material can either be a
conductor or an insulator.
Conductors and Insulators
Conductors
Insulators
 Transfers thermal heat well
 Does not transfer thermal
 Metals such as silver and
energy well.
 Non-metals such as: wood,
wool, straw, clothes,
blankets, air and paper are
good examples.
 They slow the transfer of
heat.
stainless steel are good
conductors
 A good conductor, such as
a tile floor, feels cool to the
touch because it easily
transfers heat away from
your skin.