towards an analysis of errors made by university students ... - DSpace

purposes it is ideal.
The electric motor has one great disadvantage;
it
has to be supplied with electricity.
It must either be connected
to an electric supply line or to a very heavy battery. This
is
why the electric motor is unsuitable
for cars, motor cycle and
so on. But many machines do not need to be moved about, or
at
any rate they can be attached to a power point. For all
these
machines the electric motor can be used.
T2P - Text number 2 - Physics
CORROSION
This is the slow, gradual attack made on the surfaces
of metals and alloys by the atmosphere or by the water. The
best
known example
is the rusting of ordinary iron and steel, but most
metals corrode, though some more slowly than others. Tens of
thousands of iron and steel are washed into the sea as rust from
the United Kingdom alone, and at least £50 million
is spent
annually in Great Britain in preventing corrosion,
The processes that attack exposed metals, both pure
metals and alloys are essentially chemical. The simplest of them
is tarnishing, which is usually the result of a gentle reaction
between the metal and a gas - that is, the atmosphere around us.
Sometimes oxygen combines with the metal
to form an oxide: more
frequently the air, containing traces of sulphur compounds,
reacts with the metal
to produce a thin layer of metalic
sulphide. The blackening of silver and the darkening of copper
arid brass are well-known examples of tarnishing.