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Heat Transfer Reading
Heat is the movement of energy of from one place to another. Molecules in matter are constantly moving. If
something is hot, the molecules move faster. If something is cold, the molecules move slower. When fast-moving
molecules hit slow-moving molecules, heat is transferred.
Heat moves from hotter to cooler objects. If you were to step barefooted onto a tile floor it might feel cold. You may
think the cold is moving into your foot. What really happens is heat is moving from your foot to the floor. This is
why your foot feels colder.
For heat to move, it must have a medium. A medium is something heat moves through. For example, heat moves
through metal. Metal is medium.
Heat can move from one object to another in three ways…
conduction.
convection.
radiation.
Conduction is when heat moves from one object to another by direct contact. Think of a time you have burned your
hand by touching a hot spoon in a bowl of hot soup. The hot water transfers its heat through molecules bumping
into each other. This continues until the spoon and soup are the same temperature.
For there to be heat transfer through conduction, you must have a conductor. A conductor is something through
which heat moves. Metals are excellent conductors of heat.
Eggs and sausages frying in a pan
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Convection is the rising of the hot and falling of the cold. Convection occurs only in liquids and gases. Think of the
furnace that keeps your home warm.
As the air is heated, it rises. When it cools off, it falls. The air is heated again and rises. The process continues,
keeping your home warm.
Convection requires a medium. That medium is always a liquid or gas. Examples of convection include boiling water,
winds, ocean currents, and hot air balloons.
Boiling water
Wind
Ocean currents
Hot air balloon
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Radiation is the transfer of heat by electromagnetic waves. It does not require a medium in which the energy is
transmitted. The Sun is the best example of heat through radiation.
The heat waves produced by radiation from the Sun travels through space. It does not become heat until the heat
wave strikes an object. The energy produced by the collision is heat.
Another heat source that produces radiation is fire.
As you can see, radiates out in all direction.
When a heat wave hits an object, the heat is absorbed (absorption). The
object retains the heat produced by the heat wave. This is why you don’t
want to wear dark colors in the summer. A dark color absorbs more heat,
making you warmer. A lighter color absorbs less heat and you are cooler.
How do you stop the movement of heat? You use insulation. Something
that stops the movement of heat is called an insulator. Examples of an
insulator is a thermos, Styrofoam, plastic, and rubber.
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Principles of Heat Study Guide Review Sheet
Vocabulary You Should Know and Use
Absorption – Retaining heat.
Conduction – Movement of heat through an object in contact.
Conductor – An object that will allow heat to travel through it.
Convection – Rising of hot air and falling of cold air.
Heat – Movement of thermal energy of from one place to another.
Medium – Something through which heat moves.
Insulator – An object through which heat cannot pass (example – cork).
Radiation – Heat energy traveling through space/air (heat from the sun or heat from a campfire).
Movement of Heat
Heat moves from the hot object to the cold object.
Heat must have something to move through.
1. This is called a medium.
Three Types of Heat Transfer
Conduction
1. The movement of heat through objects that are touching.
a. Both objects must be heat conductors.
1) A conductor is something through which heat travels.
Convection
1. Rising of hot air/liquid and falling of cold air/liquid.
2. Gets hot because particles in the object begin to move faster.
Radiation
1. The transfer of energy by electromagnetic waves.
a. Can’t feel heat until waves hit an object.
Absorption (Absorb) of heat
1. When the heat wave hits an object, the heat is absorbed by that
object.
a. Dark colors are better absorbers and the object gets warmer.
b. Light colors are poor absorbers and the object does not get as hot.
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Key Points to Remember
Conduction
Heat transfer through direct contact with heat source.
Must move through a conductor.
Moves from the heat source to the end of the conductor.
Convection
Heat transfer through hot gas/liquid rising and cold gas/liquid falling.
No gas or liquid – no convection.
Radiation
Heat transfer through heat (electromagnetic wave)
Does not become heat until wave hits an object.
Can travel through a vacuum (outer space) and gas.
Examples of Heat Conductors
Aluminum
Brass
Copper
Gold
Iron
Metal pots and pans
Platinum
Silver
Examples of Heat Conduction
A cold penny warming up in your warm hand.
A hot iron being placed on top of a wrinkled
shirt.
A metal hanger getting hot when cooking a hot
dog in a fire.
A plate heating up when hot food is placed
upon it.
An ice cube in your hand.
Cast iron skillet a stove’s burner.
Hot handle of a metal pot or pan.
Metal poker in a fire.
Walking on hot asphalt in your bare feet.
Examples of Heat Insulators
Air
Ceramic
Glass
Plastic
Porcelain
Rubber
Water
Wood
Examples of Heat Radiation
Heat from the sun warming your face.
Heat from a lightbulb.
Heat from a fire.
Roasting something over a campfire.
Examples of Heat Convection
Earth’s atmosphere.
Earth’s convection currents (hot magma rises;
cold magma falls).
Heating water on a stove.
Heating your house.
Hot air balloon.
Pond – cold water falls, hot water rises.
Refrigerator.
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