Worlds of David Darling > Children's
Encyclopedia of Science > From Glasses to Gases > Chapter 1
FROM GLASSES TO GASES:
The Science of Matter
a book in the eXperiment! series by David Darling
1. Matter of Interest
Think about how many different materials we use in our everyday lives –
wood, paper, plastic, metal, glass, cotton, rubber, stone, and dozens of
others. Some of these materials are natural, the rest are human-made.
| Matter is all around us,
in both human-made and natural things
How we use a substance depends upon its properties. For instance, rubber
works well for the sole of an athletic shoe because it bends and then goes
back to its original shape. It also grips well and is very tough. Glass,
on the other hand, would make a terrible shoe, but is ideal for use in windows.
Scientists spend a lot of time trying to develop new materials to do new
jobs or to do old jobs better. This has led to such breakthroughs as nonstick
frying pans, toughened glass, heat-resistant tiles for the space shuttle,
and even clothes that change color.
Three States of Matter
Everything around us – every material or substance – is made
of MATTER. Matter is anything that takes up space. It can exist in three
states: SOLID, LIQUID, or GAS. Under normal conditions, most substances
occur in just one of these states. For example, we think of iron as being
a solid. But if it is heated enough, iron will turn into a liquid, and eventually
into a gas. As a substance changes its state, so do many of its properties.
All substances are made up of tiny particles called ATOMS. In most substances,
atoms are joined together in groups known as MOLECULES.
Molecules are always moving. In a solid, the molecules are very close together
and can only vibrate in fixed positions. In a liquid, the molecules are
usually a bit farther apart and can move around one another. In a gas, the
molecules are far apart and are able to dart rapidly in any direction.
You will need:
- A collection of small pieces of materials of different kinds,
such as wood, plastic, rubber, steel, copper, glass, stone, leather,
cardboard, pencil lead (graphite), and cork
- A bowl of water
- A nail
- A magnet
- A bulb holder and bulb
- Four pieces of wire
- A battery
- A block of wood
- Two thumbtacks
- Several pieces of different kinds of fabric
What to do:
Choose one of the materials. What is its color? Is it rough, dull,
or shiny? Use the nail to find out whether the material is easy to
scratch. Does the material float when placed in the bowl of water?
Is it attracted by the magnet?
Connect the light bulb to the battery. Join two of the wires to the
battery and then to the block of wood, using the thumbtacks as shown.
Test to see if electricity will pass easily through the material by
laying it across the thumbtacks. The bulb will light up if electricity
can get through.
Repeat these tests with the other materials. Make a table of your
results under the headings shown. Arrange the materials in groups
according to their properties. For example, you might group the materials
under the headings "Easy to Scratch" and "Hard to Scratch" and the
under the headings "Will Float" and "Will Not Float." Do the materials
that scratch easily also tend to be the ones that will float? If so,
can you suggest an explanation? Make other such comparisons and try
to explain your results.
Taking it further:
Think about other properties that materials possess. Devise your own
experiments to test these properties.
Collect several pieces of different kinds of fabric. Design an experiment
to find out which of the fabrics is the hardest-wearing.
It is interesting to look at the ideas that different people come
up with when asked to design an experiment. Take the case of an experiment
to measure which group of fabrics is the most hard-wearing. Different
pupils in a class will design different ways to carry out this test.
Which is the best? Sometimes an idea for an experiment does not work
well in practice because the equipment is too complicated, or is simply
wrong for the job. In other cases, the experiment does not isolate
the topic of interest properly. If other factors are allowed to interfere
with the results in an unpredictable way, the experiment is not fair."
One method of finding out how well various fabrics wear is to use
a brick and a thick newspaper (to help keep the brick in place). Put
the newspaper on a table and place the brick in the center of the
newspaper. Hold each piece of fabric at either end and rub it backward
and forward across the brick. Keep a record of how many rubs it takes
to make a small hole in the material. Your test will only be fair
if the rubs are equally hard and you use pieces of fabric the same
size. Does a cotton sweater last longer than a woolen one? Does brand
A of jeans wear better than brand B? Set goals for your experiment
and present your results in a clearly written report.
Little and Large
Atoms and molecules are much too small to be seen individually by the human
eye. But we can certainly see the effect of trillions and trillions of these
tiny particles together.
The properties of a substances are related to the properties of its molecules.
For example, a hard-wearing material is one whose molecules are bound firmly
together. A material, such as steel, that can be turned into a magnet is
one whose molecules can behave like miniature magnets. A substance that
is yellow contains molecules that reflect mostly yellow light.
Diamond: A Hard Act to Follow
Diamonds, pencil lead, and charcoal may not look much alike, but they are
all made from the same kind of atoms: carbon atoms, In diamonds, the carbon
atoms are linked by very strong bonds. This makes diamonds extremely hard.
Another reason for their hardness is that the atoms are not arranged in
layers, so they cannot slide over one another. Each carbon atom is at the
center of a triangular pyramid, surrounded by four other atoms at the corners
of the pyramid. This pattern repeats itself millions and millions of times,
so a diamond is really a single giant molecule.
|In diamond, carbon atoms are arranged in
a the shape of pyramids
Diamonds are the hardest substance known. This makes them ideal for use
in cutting equipment, such as glass cutters and diamond-edged saws. Powdered
diamonds are also used as abrasives for smoothing very hard materials. Diamonds
are found in rocks in certain parts of the earth, but they can also be made
artificially in laboratories. Good, natural diamonds are extremely rare
and are used mostly in jewelry.
You will need:
- Small samples of different materials, including expanded polystyrene
(the white, crumbly material used in packaging), cork, plastic,
wood, stone, iron, and lead
- An apple, an orange, a beet, an onion (or any other types of
fruits and vegetables that are available)
- A bowl of water
What to do:
Weigh each object in your hand. How heavy does it feel? Put it in
the bowl of water. Does it float or sink? How well does it float,
or how quickly does it sink? Keep a record of your results. Investigate
other materials in the same way.
Dense, Denser, Densest
Polystyrene and cork feel light. Metals feel heavy. This is because metals
are more dense.
Density is a measure of how much matter is contained within a certain volume.
Water has a density of 1.3 ounces per cubic inch. Anything will float in
water if its density is less than the density of water. Look at the table
of densities and you will see why a cork floats and a stone sinks.
Fruits and vegetables contain mostly water, so they either sink or float.
Fro example, apples and oranges ten to float, but carrots and tomatoes tend
to sink. Oranges sometime sink when peeled because the fruit is denser than
A substance may be dense because it contains heavy atoms, or because its
atoms are packed closely together, or for both of these reasons. Are denser
substances harder than less dense ones? Some they are. For example, stone
is harder than polystyrene. On the other hand, lead and gold are both much
softer than iron, even though they have higher densities. Hardness is decided
not just by how well a substance's atoms are packed together but by how
strongly they are bonded.