Transcript Heat - Warren County Schools

HEAT
AND
HEAT
TRANSFER
What is the difference between
temperature and heat?
Temperature is a
measure of the average
kinetic energy of
atoms.
Thermometers
are used to
measure
temperature
This means: the
higher the
temperature, the
faster the atoms
move the lower the
temperature, the
slower the atoms
move
Less Heat
More Heat
If energy is added to atoms, they move
faster. The faster they move, the further
apart they move. This spreading out of atoms
happens in solids, liquids and gases. The term
for this type of expansion is called THERMAL
EXPANSION.
Thermal expansion is why running a tight jar
lid under water loosens the lid. Read pgs. In
the textbook to see other examples of thermal
expansion.
WHAT IS HEAT?
The ancients used to think
that heat was an invisible,
weightless fluid that
flowed from hot things to
cold things.
ACTUALLY
Heat is transfer of
energy between objects
of different
temperatures caused by
atoms rubbing together
How cold is cold?
There is no such thing as coldness. What
we call cold is really absence of heat or
slow atoms. Even when it is 15 degrees
outside, that is 15 degrees of HEAT,
NOT 15 degrees of COLD.
Another word for heat is
THERMAL ENERGY.
Heat (thermal energy) is transferred from
warmer objects to cooler objects
Can a balanced temperature ever be reached?
YES, IT’S CALLED THERMAL
EQUILIBRIUM
No energy transfer occurs
HEAT IS TRANSFERRED IN
THREE WAYS
BY
CONDUCTION
CONVECTION
RADIATION
CONDUCTION
Transfer of heat from one substance to
another by direct contact of molecules.
Happens in solids, liquids and gases
Best conduction happens in solids
Examples: Sauce pan on a stove top, metal
spoon in a bowl of soup, ice melting in a
warm hand, hot shower, walking on hot coals
Objects that heat up
easily are called
CONDUCTORS.
Metals are the best
conductors
Metal objects feel
cold because they
conduct heat AWAY
from your hand
Objects that DO NOT
heat up easily are
called INSULATORS.
Things like glass,wood,
plastic and rubber are
good insulators
Which parts of the pan are conductors and which
are insulators?
CONVECTION
 Transfer of heat in liquids and gases ONLY
 Heat moves up and down in a motion called a
CONVECTION CURRENT
 Heated liquids and gases are less dense &
rise carrying heat with them
 Examples: movement of plate, ocean
currents, home furnace heating & circulating
air
Convection Currents in
The house
Convection Current
Convection currents cause the Earth’s tectonic plates to move about.
RADIATION
 transfer of heat through empty space in form of
infrared radiation waves (what we think of as heat
waves)
 When light strikes an opague object, it converts
into heat
 Examples: blacktop heats up on a sunny day, hot
sand on a beach, electric heaters.
Explain how each of these uses radiant heat.
How does heat affect matter?
Physically: heat changes the state in which
matter exists i.e. melting, freezing,
evaporating, condensing
Chemically: for chemical reactions to occur,
chemical bonds must be broken and new
compounds formed. Requires energy to be
absorbed or released
Effects of Heat on the Earth
Large bodies of water
moderate the climate. The
temperatures are not as
extreme!!
Ocean CurrentsCaused by convection
Currents.
Effects of Heat On the Earth
Uneven heating in the atmosphere creates wind
and storms.