Transcript Lesson 3-2 - TeacherWeb

Heat and Energy
Chapter 3 section 2
Key Concept: Heat flows in a
predictable way from warmer objects
to cooler objects until all the objects
are the same temperature.
What You Will Learn



Temperature is a measure of the
average kinetic energy of particles in
an object.
Heat is energy that is transferred
between objects.
Heat flows by conduction,
convection, and radiation.
What is temperature?



Temperature is a
measure of the
average kinetic energy
of the particles in an
object.
All matter is made up
of constantly moving
particles, such as
atoms or molecules.
When a particle is in
motion, it has kinetic
energy.



The faster particles
move, the more kinetic
energy they have.
The temperature of a
substance depends on
the kinetic energy of
all of its particles.
The more kinetic
energy the particles
have, the higher the
temperature of the
substance.

The substance
on the right has
a higher
temperature
because its
particles have a
higher average
kinetic energy.



Particles in a substance move at
random and at different speeds.
The average of all these speeds is
the average kinetic energy.
When you measure temperature, you
are measuring average kinetic
energy.



Temperature does not
depend on the amount of
particles in a substance.
A teapot holds more tea
than a tea cup.
But if the atoms of tea in
both containers have the
same kinetic energy,
then the tea in both
containers has the same
temperature.
Thermal Expantion



When particles move
faster, they move
apart.
As the space between
the particles increases,
the substance expands.
Therefore, an increase
in temperature leads to
an increase in volume.
This is called thermal
expansion.
What is heat?



Heat is the energy that is
transferred between objects
that are at different
temperatures.
Heat energy is always
passed from an object with
a higher temperature to
one with a lower
temperature.
When you touch something
hot, heat flows from the
object to your finger.



Thermal energy is
the total kinetic
energy of the particles
that make up a
substance.
Thermal energy,
which is expressed in
joules (J), depends
partly on temperature.
Something at a high
temperature has more
thermal energy than
something at a low
temperature.


Thermal energy also
depends on the
amount of particles
in a substance.
The more particles in
a substance at a
given temperature,
the greater the
thermal energy.


When things that
have different
temperatures come
into contact, energy
will always be
transferred.
Energy will pass from
the warmer to the
cooler object until
both have the same
temperature.
Ex: Hot soup makes cool bowl
hot.
How is heat transferred?



The transfer of heat from
one object to another
through direct contact is
called conduction.
Heat flows from the
particles of hot soup to
the part of the spoon
that is in the soup.
Heat travels from particle
to particle, from the soup
all the way up the
spoon’s handle.



The transfer of heat
due to the movement
of matter is called
convection.
When you boil water,
heat is passed from
the burner to the pot
and from the pot to
the water by
conduction.
As the water is
heated, it becomes
less dense.



Cooler, denser water at the top of
the pot sinks.
This forces the warmer water to the
surface.
Water continues to rise and fall in a
circular pattern called a convection
current.



The transfer of heat or
other energy as
electromagnetic waves,
such as visible light or
infrared waves, is called
radiation.
Radiation can occur
between objects that
are not in direct contact
with each other.
The sun transfers
energy through space
by radiation.
States of Matter



The states of matter are the physical
forms in which a substance can exist.
The three states of matter are solid,
liquid, and gas.
A substance’s state depends on the speed
of its particles, the attraction between
them, and the pressure around them



A substance’s chemical composition also
influences the state it is in at a given
temperature.
For example, milk is a liquid at room
temperature, but butter is a solid.
A change of state occurs when a
substance changes from one state of
matter to another.

Changes of state include:




condensing (gas to liquid)
freezing (liquid to solid)
melting (solid to liquid)
evaporating (liquid to gas)



A change of state involves a transfer
of heat from one substance to
another.
When a substance melts or boils, it
gains energy.
When a substance condenses or
freezes, it loses energy.