Download Chapter 15 – Section 2 Heat

Chapter 15 – Section 2
Heat
Pages 438 - 443
Heat and Thermal Energy
• Heat is the transfer of thermal energy from
one object to another when the objects are
at different temperatures.
• The amount of heat that is transferred
when two objects are brought into contact
depends on the difference in temperature
between the objects.
Transfer of Thermal Energy
• When heat is transferred, thermal energy
always moves from warmer to cooler
objects.
• This process of heat transfer can occur in
three ways—by conduction, radiation, or
convection.
convection
Conduction
•
Transfer of heat by direct contact is called
conduction.
conduction
•
Conduction occurs when the particles in a
material collide with neighboring particles.
particles
•
Examples:
1) A frying pan on a stove.
2) Feet on hot sand
or a cold tile floor.
3) An ice cube melting
in your hand.
Radiation
•
Heat is transferred from the Sun to Earth by
radiation.
radiation
•
Heat transfer by radiation occurs when
energy is transferred by electromagnetic
waves.
waves
•
There is no direct contact with radiation.
•
Other examples besides the Sun:
1) A fireplace
2) A lamp
Convection
•
In a gas or liquid,
liquid molecules can move much more
easily than they can in a solid.
•
The transfer of thermal energy by the movement
of molecules from one part of a fluid to another is
called convection.
convection
•
Hot fluids become less dense and rise and cooler
fluids are more dense and sink.
sink
•
This creates density currents.
currents
Natural Convection
•
Natural convection occurs when a warmer,
less dense fluid is pushed away by a cooler,
denser fluid.
•
Wind movement near a lake or ocean can
result from natural convection.
•
Thunderstorms and hurricanes are powered
by convection.
Diagram of a Convection Cells of a
Hurricane
Thermal Conductors
•
A thermal conductor is any material that easily
transfers heat.
•
Metals are typically good thermal conductors
because they have loosely held electrons that
bump into other materials and transfer heat.
•
Gold and copper are the best conductors of heat.
Thermal Insulators
•
A thermal insulator is a material that does not
transfer heat easily.
•
Liquids and gases are
usually better insulators
than solids are.
•
Fluffy insulation is put in-between walls to reduce
the amount of heat transfer between the inside
and outside of your house.
Heat Absorption
•
Why is pavement hotter than grass?
•
The change in temperature of an object as it
absorbs heat depends on the material it is made
of.
of
•
The specific heat of a substance is the amount of
heat needed to raise the temperature of 1 kg of
that substance by 1°C.
•
The specific heat of grass is higher than pavement
so it takes more heat to increase the temperature
of the grass than it does the pavement.