Worlds of David Darling > Children's
Encyclopedia of Science > Between Fire and Ice > Chapter 1
BETWEEN FIRE AND ICE:
The Science of Heat
a book in the eXperiment! series by David Darling
1. Hot Subject
Heat is everywhere: in volcanoes, in icebergs, in your body – in every
object in the universe. All matter contains heat.
| Everything contains heat: the icy slopes
of this volcano as well as its hot inside
Like light and sound, heat is a form of ENERGY. This means that it can be
used to do work and cause movement. It can also be transferred from one
object to another. For example, some of the heat tat starts out in the center
of the Sun eventually reaches the Earth and provides us with the warmth
we need to live.
Almost all the substances round you are made up of MOLECULES. These are
very tiny particles that never stop moving.
Whenever you breathe in deeply, your lungs fill with about 5 septillion
(5 and 24 zeros following it) molecules of oxygen and about 18 septillion
molecules of nitrogen. These molecules are racing around at an average speed
of about 1,500 feet per second, the speed of a rifle bullet.
As air is heated up, the molecules in it move faster. As it is cooled down,
the molecules move slower.
In a gas or a liquid, the molecules are able to move around freely. In a
solid, the molecules are stuck together. However, they can still vibrate
back and forth. As a solid is heated up, the vibrations get bigger and faster.
In any substance, whether it is a solid, a liquid, or a gas, the speed of
the molecules is a measure of how hot or cold it is.
|Molecules in a solid, a liquid,
and a gas
Molecules in Collision
In a liquid or gas, the molecules behave like bumper cars. They keep ramming
into one another and bouncing away again. If two different liquids are put
together, their molecules immediately start to collide and become mixed
up. If one of the liquids is hot, its molecules will smash hard into the
molecules of the other liquid and cause them to spread out quickly. On the
other hand, if both liquids are cool, their molecules will move more slowly
and take longer to mix together.
You will need:
- Two clear glasses
- Food coloring
- An eyedropper
What to do:
Fill one of the glasses with cold water and the other with hot water.
Suck up a small amount of food coloring into the eyedropper. Put the
end of the eyedropper in the middle of the glass of cold water and
gently squeeze out a drop of food coloring. Do the same in the glass
of hot water. Compare what happens in the two glasses. Try to explain
what you see.
Hot Air, Cold Air
You will need:
- A balloon
- An empty glass bottle
- Two large plastic bowls
What to do:
Take the cap off the bottle and place the balloon over the top. Fill
one of the bowls with cold water and the other with hot water. Place
the bottle in the hot water. Does anything happen to the balloon?
Now place the bottle in cold water. What happens? Try to explain your
Heat and Gases
As a gas is heated up, its molecules move faster. They collide harder and
more often among themselves. They also collide harder and more often with
the walls of their container. If the container is made of a stretchy material,
such as rubber, it will expand as the gas inside gets hotter. If the container
is stiff, as the gas inside heats up, its molecules will not be able to
make the container bigger. Instead the gas molecules will just push harder
and harder against the walls.