Download Heat and its Transfer Study Guide

Heat and its Transfer Study Guide
It is a sunny day outside. The sun’s rays warm the Earth. The sun is a star made up of
hot, glowing gases. It is the main source of heat and light on Earth. Energy from the sun
is called solar energy and is transmitted by waves of radiation. Heat is a kind of energy
that moves from one place to another. There are many other ways that heat is made on
the Earth.
Heat is a form of energy that moves through the air. Sometimes, when two things come
into contact with each other, heat is produced. For example, rub your hands together
quickly. Your hands feel warm. Heat has been made. When you rub your hands
together, you create friction. Friction is a force that results when two things are rubbed
together.
Heat is actually the flow of energy. This energy moves from one place to another. Heat
always moves from a warmer object to a colder one. Think about a cup of hot tea. You
put a cold metal spoon in the water. Soon the spoon becomes warm. Heat has moved
from the hot tea to the cold spoon. The transfer of thermal energy (heat) between two
objects that are touching is called conduction. For example, a frying pan sitting on a
stove would be a type of conduction. Convection is the transfer of thermal energy by the
movement of liquids and gases. For example, the heating vent in your home moves heat
throughout your house, but you don’t see it.
Suppose you put a pot of water on the stove. You turn up the heat and the water begins
to boil. You put a metal spoon in the water. You also put a wooden spoon in the water.
Heat from the water moves to the two spoons. But one spoon feels hotter. Why is one
spoon hotter than the other? If you touched the metal spoon it would feel very hot. But
the wooden spoon would not feel hot at all. That is because metal is a conductor of heat.
The wooden spoon is not. Conductors of heat are materials through which heat moves
easily. Metals are good conductors of heat. Copper, iron, silver, and aluminum conduct
heat very well. Most cooking pans are made of metal. The heat moves quickly through
the metal and warms the food.
If you touch the wooden spoon in the boiling water, it will not feel hot. This is because
wood is an insulator of heat. Insulators are materials that heat cannot move through
easily. Materials like wood and plastic are good insulators of heat. Foam is a good
insulator of heat too. Cloth is a good insulator of heat. Think about going outside when
it is cold. You wear thick wool clothes to keep warm. The wool insulates you from the
cold. You use a potholder to touch a pan that is hot. The potholder keeps the heat from
burning your fingers. Fur is a good insulator of heat. Fur keeps animals warm. The fur
traps heat and keeps it from leaving the skin of an animal. You have insulation in your
house to trap heat and keep it from leaving your house. Rubber is also a good insulator
of heat. Many metal wires are covered with rubber. This keeps the heat of the metal
wires from getting too hot.
Heat from the sun gives energy to molecules. A molecule is a tiny part of matter.
Energy makes molecules move faster. When the molecules move faster, the matter
changes in some way. When soil becomes too dry, it can crack. The hat from the sun
makes the molecules of the rock or soil move faster. When molecules move faster, the
rock or soil expand, or get larger in size. A crack in the rock would be a clue that a rock
has expanded in size. Heat from the sun can also make a puddle of water evaporate.
Evaporate means a liquid changes to a gas. The puddle disappears because the water
goes into the air.
When you go outside, you often want to know the temperature, or the measure of how
hot or cold it is. The higher the temperature, the warmer you feel. To measure
temperature, you use a thermometer. A thermometer is a thin glass tube that is filled
with a liquid. The scale on a thermometer is marked in degrees. When the temperature is
hot, the liquid inside the thermometer expands, or get larger. This makes the liquid rise
up in the glass tube. When it gets colder, the liquid goes down. Some thermometers are
marked in units called Fahrenheit, which is most likely the kind you have in your home.
Other thermometers are marked in units called Celsius. Most scientists use Celsius
thermometers. Water boils at 212°F and at 100°C. Water freezes at 32°F and 0°C. Your
body temperature is 98.6°F.