Transcript Heat Transfer - Mrs. Nicolai's Science Class

HEAT TRANSFER
Conduction, Convection, and Radiation
State Science Standard
• Students know heat energy flows from
warmer materials or regions to cooler ones
through conduction, convection, and
radiation
Objectives
• Explain conduction, convection, and radiation
using terms of heat transfer.
• Given a scenario involving heat transfer,
recognize conduction, convection, and radiation.
• Compare different materials and their ability to
transfer heat.
• Understand the properties of conductors and
insulators.
Temperature
• What are you measuring when you take someone’s
temperature?
• Here is a hint: When we studied the states of matter,
we learned that particles speed up as they change
from a solid to a liquid, and then to a gas.
• Temperature is a measure of the average kinetic
energy of the individual particles in matter.
• When you heat a thermometer, the particles in the
liquid inside the thermometer speed up and take up
more space. The liquid then rises up the tube.
Thermal Energy
• If you were to compare the amount of kinetic
energy in a cup of water to the amount of kinetic
energy in the Pacific Ocean, which has more
energy? Why?
• The ocean has more kinetic energy than a cup of
water because it has more particles that can
move.
• The total energy of all the particles in an object is
called thermal energy.
Thermal Energy
• The thermal energy of an object depends on
three things:
• the number of particles in the object
• the temperature of an object
• the arrangement of the object’s particles (not going to worry
about this one this year)
Which one has more thermal energy, a mug of hot cocoa at
75 degrees Celsius or a large pot of hot cocoa at 75
degrees Celsius?
Which one has more thermal energy, 100 mL of boiling
water or 100 mL of cold water?
Heat
What does your mom tell you when you leave the front
door open on a cold day?
Heat is thermal energy moving from a warmer object to a
cooler object.
Technically, you are letting out the thermal energy during
this heat transfer (not letting the cold air in).
If two objects have different temperatures, heat will flow
from the warmer object to the colder one.
Conduction
• In the process of conduction, heat is transferred
from one particle of matter to another without the
movement of matter.
• This is how a pot gets hot when sitting on a stove.
• The fast-moving particles in the hot electric coil of
the stove collide with the slow moving particles in
the cool pot. The transfer of heat causes the
pot’s particles to move faster.
• Let’s demonstrate this by passing a gentle push
around the classroom.
Convection
• In convection, heat is transferred by the
movement of currents within a fluid.
• Remember density? Is warm air more or less dense than
cool air?
• When you heat water on the stove, the water at the
bottom of the pan heats faster than at the top. The water
at the bottom becomes less dense and floats to the top. It
then cools because it is farther away from the heat source
and sinks back to the bottom.
Convection
• This flow creates a circular motion known as a convection
current.
Cooler
water
sinks
because
it is more
dense
This creates
a convection
current
Warmer
water
rises
because
it is less
dense
Radiation
• Radiation is the transfer of energy by electromagnetic
waves.
• Unlike conduction and convection, radiation does not
require matter to transfer thermal energy.
• This is why the sun’s energy can reach Earth. It can
travel through empty space (no matter required).
Conduction, convection, or radiation?
• You sit by the fire to get warm.
• As you sit on the beach by the ocean, a wind comes up.
• You burn your hand when you grab the spoon sticking up
out of the soup on the stove.
• You cook your Totinos pizza rolls in the microwave.
• Even on a cold, sunny day, the inside of the car feels
warm.
• You take a ride in a hot air balloon.
Conductors and Insulators
• A material that conducts heat well is called a conductor.
• Would you rather grab a metal spoon or a wooden spoon
that has been sitting in a pot of boiling soup?
• A material that does not conduct heat well is called an
insulator.
• Would you rather wear a down jacket or a sheet of
aluminum foil on a very cold day?