Charge
Outside of the nucleus
of the atom there are only two fundamental forces acting in the physical
world: the Graviational Force and the Electrostatic Force. The gravitational force governs the behaviour of
mass and the electrostatic one governs the behaviour of charges!
You are used to gravity
because you have mass in 'your world' and it acts on that mass all of the time and you see the effects. You are
not so aware of the electrostatic force because it only acts on you when
you have a net charge - a static charge.
There are only
two types of charge. They are opposite to each other and are called
'positive charge' and 'negative charge'.
Charge is a special
property that electrons and protons have. (At advanced level you will
hear about other charged particles too - but you don't come across them until
then!).
Matter (all solids,
liquids and gases) is made up of atoms.
Atoms are composed of protons, neutrons and electrons. As atoms
are made up of electrons and protons in equal number atoms the charge
of an atom is zero - it is called a neutral atom.
Electrons
have negative charge.
Protons
have positive charge.
(Neutrons
have no charge)
Ions
- In an
anion the atom gains an electron - it has a net negative
charge - it is attracted to an anode.
- In a cation
the atom loses and electron - it has a net positive charge - it is attracted to a cathode.
The electrostatic
force
Oppositly charged
objects attract each other and like repel
Charged objects experience
a force from all other charged objects. The closer the object it the bigger
the force experienced and the bigger the charges involved the stronger
the force. Uncharged objects don't 'feel the force' at all! This force
is called the electrostatic force.
This electrostatic
force is in addition to the force of gravity the object feels because
of its mass. Therefore, if a charged object has very little mass the electrostatic
force it experiences may be bigger than the gravitational force. If this
electrostatic force acts in the opposite direction to gravity the object
may be seen 'defying gravity'!
Examples:
When you charge up your body by touching the Van der Graaf generator your
hair stands on end. This is because the hair strands all gain the same
electric charge and repel each other. The force of repulsion is so great
that it exceeds the weight of each hair strand. Your arms do not lift
away from your body though - even though they have the same charge as
your body. This is because they are too heavy!
Take a look at the Electrostatic
Levitator at NASA's Marshall Space Flight Center in Huntsville