When you are at the beach, you can see the water waves moving up and
down when the tides come in. The waves are transverse: they move at 90⁰
to the direction they are travelling in. The same effect can be created when
hold a piece of rope at one end and wiggle it up and down. The up and down
motion is called undulation. Water waves can reflect or bounce off a surface.
For example, the water waves in a bath hit the sides of the bath tub and
When two waves meet each other, the overall shape of the wave changes.
They can add or cancel each other. This is called superposition. When two
waves come together that are in phase with each other, the waves add to
make a higher wave with a greater amplitude. When two waves come together
that are out of phase, the waves cancel each other out, and so there is no
Sound waves are different to water waves, they are longitudinal. They can
only travel through solid, liquid or gas. This means that there is no sound in a
vacuum. A vacuum is an enclosed empty space where there is no air. The
speed of sound through solids, liquids and gases is different. It is the measured
in the same way we measure the speed of moving objects – distance / time
taken. Sound travels faster through solids than liquids or gases as the
particles are closer together.