• The particle model of a Gas
• A gas has no fixed shape or volume, but always
spreads out to fill any container.
• There are almost no forces of attraction between the
particles so they are completely free of each other. The
particles are widely spaced and scattered at random
throughout the container so there is no order in the
system. The particles move rapidly in all directions,
frequently colliding with each other and the side of
the container. With increase in temperature, the
particles move faster as they gain kinetic energy.
The particle of a liquid
• A liquid has a fixed volume at a given temperature but its
shape is that of the container which holds the liquid.
There are much greater forces of attraction between the
particles in a liquid compared to gases, but not quite as
much as in solids. Particles quite close together but still
arranged at random throughout the container, there is a
little close range order as you can get clumps of particles
clinging together temporarily. Particles moving rapidly in
all directions but more frequently collisions with each
other than in gases due to shorter distances between
particles. With increase in temperature, the particles
move faster as they gain kinetic energy, so increased
collision rates, increased collision energy and increased
rate of diffusion.
The particle model of a Solid
• A solid has a fixed volume and shape at a
particular temperature unless physically
subjected to some force. The greatest forces of
attraction are between the particles in a solid
and they pack together as tightly as possible in a
neat and ordered arrangement. The particles are
too strongly held together to allow movement
from place to place but the particles vibrate
about their position in the structure. With
increase in temperature, the particles vibrate
faster and more strongly as they gain kinetic
• In evaporation* and boiling the highest kinetic energy
molecules can ‘escape’ from the attractive forces of the
other liquid particles.
• The particles lose any order and become completely free
to form a gas or vapour.
• Energy is needed to overcome the attractive forces in the
liquid and is taken in from the surroundings.
• If the temperature is high enough boiling takes place.
• Boiling is rapid evaporation anywhere in the bulk liquid
and at a fixed temperature called the boiling point and
requires continuous addition of heat.
• The rate of boiling is limited by the rate of heat transfer into
• On cooling, gas particles lose kinetic energy
and eventually become attracted together to
form a liquid.
• There is an increase in order as the particles
are much closer together and can form
clumps of molecules.
– This is why steam has such a scalding effect, its
not just hot, but you get extra heat transfer to
your skin due to the exothermic condensation on
• When a solid is heated the particles vibrate more
strongly as they gain kinetic energy and the particle
attractive forces are weakened.
• Eventually, at the melting point, the attractive forces
are too weak to hold the particles in the structure
together in an ordered way and so the solid melts.
• The particles become free to move around and lose
their ordered arrangement.
• Energy is needed to overcome the attractive forces
and give the particles increased kinetic energy of
• On cooling, liquid particles lose kinetic
energy and so can become more strongly
attracted to each other.
• Eventually at the freezing point the forces of
attraction are sufficient to remove any
remaining freedom and the particles come
together to form the ordered solid
• Light is a form of energy produced by the change
in motion of a charged particle. Light does not
need a medium (solid, liquid or gas) in order to
travel. Electrons moving back and forth will cause
light. When the electrons inside of an atom
absorb energy they jump to a different energy
level. When these electrons fall back down to
their original energy level they give off a little
packet of energy in the form of light. This packet
of light energy is called a photon. Light can either
travel as a wave or as a particle.
• Some objects produce their own light will other
objects reflect light. These sources of light are
called laminated objects. Sources of light include:
the sun, a light bulb, a match and a candle.
Bioluminescent organisms are living things that
can produce their own light. A firefly is an
example of a bioluminescent organism. Objects
that reflect certain amounts of light are called
illuminated objects. Objects that reflect light
include: a mirror, the moon and a piece of paper.
• What is so amazing about light is the speed at
which it travels. Light travels 186,000miles per
second or 299,798 kilometers per second. That
means light can travel a distance of 186,000 miles
in one second! It takes eight minutes for light
from the sun to reach earth. This is why you hear
lightening before you see thunder. Lightening and
thunder happen at the same time, yet light
travels faster than sound so you see the
lightening then a few seconds later you hear the
• When you wake up in the morning and look at yourself
in there mirror you are seeing a reflection of yourself.
You see your self by the light waves bouncing off of the
mirror. Reflection is the bouncing back of a wave. As
we see in the diagram to the left. Light waves hit a
smooth surface and bounce off with the same angle in
which they hit the surface. This is the Law of Reflection:
the angle of incidence is equal to the angel of
reflection. Since both angles are equal the image
appears to be the same. This will happen when we
reflect light off of a flat smooth surface.
• What happens when the surface is not
smooth? When light bounces off of a rough
surface diffuse reflection is seen. Objects
appear blurred, like the reflection of the
setting sun on the water. We do not get a clear
picture of the sun as we would if the light was
being reflected off of a mirror.
• Surfaces can also be curved. A satellite dish is
a perfect example of a concave surface. The
dish is curved inward as to direct all of the
light waves in toward the center receiver and
then through a cable into your house.
• A security mirror is curved outward (convex
surface) as to see the entire store. If you go
into 7-11 you will see a curved mirror in the
corner. This mirror is designed to spread out
the light waves so the clerk can see everything
going on in the store.
• White light contains all colors of the spectrum.
The image of the prism to the left shows white
light entering. The light waves change speed
and direction as they pass through the prism.
Each of the different colors of light then
• The colors we see are just reflections of light
off of objects. If an object reflects all
wavelengths of light then it will appear white.
If an object absorbs all wavelengths of light it
will appear black. An object is the color of
light it reflects. All other wavelengths of light
For example, a red object reflects red light and
absorbs orange, yellow, green, blue, indigo
and violet. A green object reflects green light
and absorbs red, orange, yellow, blue, indigo
Heat and temperature
• Temperature is a measure of heat energy.
Temperature is measured in degrees Celsius
(Centigrade), Fahrenheit, or Kelvin.
Some high temperatures:
Boiling water at sea level = 100 degrees
Molten lava = 2,000 Kelvin;
Tungsten filament of a light bulb = 4,000
• Silver melts at 962 degrees Celsius and boils at
2,210 degrees Celsius; Gold melts at 1,064
degrees Celsius and boils at 2,900 degrees
• Some warm-blooded animals hibernate during
cold weather and their body temperature falls
to conserve energy. The normal temperature
of a hibernating dormouse falls from 98.6
degrees Fahrenheit to 64 degrees; The normal
temperature of an opossum falls from 95
degrees Fahrenheit to 50.9 degrees
• Cold-blooded animals lack internal
temperature controls so they bask in the sun
to keep warm and then hide in the shade to
keep cool. They are most active when their
body temperatures are greater than 90
degrees Fahrenheit. The salamander is cold-
blooded and can survive in temperatures of
42.4 through 79.7 degrees Fahrenheit.
• Does hot water freeze faster than cold water?
No, it does not. However, boiled water has
less dissolved air and fewer air bubbles; for
this reason water that has been boiled might
freeze faster and will form ice that is more
• Heat is a form of energy. There are several
physical effects of heat including: 1. Changing
the temperature of a substance; 2. Changing
the state of a substance (as from solid to
liquid); 3. Causing expansion of the substance
• Heat is transferred from a substance at a
higher temperature to one at a lower
temperature by conduction, convection, or
radiation. Conduction occurs mainly in solids;
convection occurs in fluids, and radiation
occurs through space, Radiation occurs
without the need for any substance to transfer
• A magnet is an object or material that attracts
certain metals, such as iron, nickel and cobalt.
It can also attract or repel another magnet. All
magnets have North-seeking (N) and South-
seeking (S) poles. When magnets are placed
near each other, opposite poles attract and
like poles repel each other. Various electrical
devices make use of magnets.
• Types of magnets
• There are permanent magnets, temporary
magnets and electromagnets.
• Permanent magnets
• A permanent magnet is one that will hold its
magnetic properties over a long period of
• A temporary magnet is one that will lose its
magnetism. For example, soft iron can be
made into a temporary magnet, but it will lose
its magnetic power in a short while.
• By wrapping a wire around an iron or steel
core and running an electrical current through
the wire, you can magnetize the metal and
make an electromagnet. If the core is soft
iron, the magnetism will diminish as soon as
the current is turned off. This feature makes
electromagnets good for picking up and
dropping objects. Typically DC electricity is
used, but AC current will also result in an
• Properties of magnets
• Magnets always have two poles, come in various
shapes, and attract or repel other magnets.
• Names of poles
• All magnets have a North-seeking pole (N) and South-
seeking pole (S). In a compass, the side marked (N) will
point toward the Earth's North magnetic pole. Thus, it
is called the "North-seeking pole." Also note that the
Earth's North magnetic pole is not the same thing as
the North Pole. They are actually several hundred miles
• The magnet can be made into various shapes.
The bar magnet is the most common
• Bar magnet
• Magnets also can be square, spherical, shaped
like a horseshoe, and even shaped like a
• Horseshoe magnet
• If you put an iron plate across the N and S poles
of a horseshoe magnet, that would essentially
"short circuit" the effect of the magnetism, such
that its strength would not be very great. As soon
as the plate was removed, the magnet would
regain its full strength. That method is sometimes
used in magnets that are temporary to help keep
their magnetic properties for a longer time.
• An interesting characteristic of magnets is that
when you cut a magnet into parts, each part
will have both N and S poles.
• Bar magnet cut into three parts
• Attraction and repulsion
• Magnets strongly attract iron, nickel and
cobalt, as well as combinations or alloys of
• Also, unlike poles of two magnets will attract, but like
poles will repel. Thus, N and S attract, while S and S will
repel each other.
• Creating a magnet
• You can magnetize a piece of steel by rubbing a magnet
in one direction along the steel. This lines up the many
of the domains or sections of aligned atoms in the
steel, such that it acts like a magnet. The steel often
won't remain magnetized for a very long time, while
the true magnet is "permanently" magnetized and
retains its strength for a long time.
• If you use soft iron or steel, such as a paper clip, it will lose
its magnetism quickly. Also, you can disorient the atoms in
a magnetized needle by heating it or by dropping the
needle on a hard object.
• The first true application of a magnet was the compass,
which not only helps in navigation by pointing toward the
North magnetic pole, but it is also useful in detecting small
magnetic fields. A compass is simply a thin magnet or
magnetized iron needle balanced on a pivot. The needle
will rotate to point toward the opposite pole of a magnet. It
can be very sensitive to small magnetic fields.
• Other uses
• Magnets are found in loudspeakers, electrical
motors and electrical generators.
• A very common application of magnets is to stick
things to the refrigerator. Since the outer shell of
most refrigerators is made of steel, a magnet will
readily stick to it. The type of magnets used often
consists of a thin sheet of a magnetic material.
• As a novelty, magnetic disks can be stacked on a
pencil to show magnetic levitation.
• Summary for magnets
• A magnet attracts iron, nickel, cobalt and
combinations of those metals. All magnets
have North-seeking (N) and South-seeking (S)
poles. When magnets are placed near each
other, opposite poles attract and similar poles
repel each other. Magnets are found in many
of our electrical appliances.