Many different kinds of energy travel in waves. Sound waves
carry noises through the air to our ears. SEISMIC WAVES travel
inside the Earth and cause earthquakes. Light, heat, radio, and similar types
of energy are carried by a variety of waves in the ELECTROMAGNETIC SPECTRUM. Some energy waves need a medium, such as water or air, through
which to travel. The medium moves back and forth as waves carry energy through
it, but it does not actually travel along with the wave.
When an ocean wave crashes against the shore, it releases a large
amount of energy. Ocean waves are transverse waves that carry huge amounts of
energy across the surface of the sea as they move up and down. A wave 3 m
(10ft) high carries enough energy to power around 1,000 lightbulbs in every 1 m
(3 ft) of its length.
BIOGRAPHY: HEINRICH HERTZ German, 1857-1894
In 1887, physicist Heinrich Hertz became the first person to prove
that waves carry electromagnetic energy between two places. This extremely
important finding eventually led to the development of radio and television.
Hertz did not live to see these inventions, however. He died in 1894, aged only
36.
Radios, televisions, mobile phones, and radar use signals
made up of electromagnetic waves. These are waves that carry energy as
electricity and magnetism at the speed of light. Light we can see is also an
electromagnetic wave, but other types of electromagnetic wave are invisible.
The various types of electromagnetic wave have different frequencies and
wavelengths. Together, they make up the electromagnetic
spectrum.
These are produced by radioactivity. They have a short wavelength
and a high frequency and carry large amounts of energy. They are very harmful
and can cause cancer in humans and animals.
These invisible waves are slightly shorter than visible violet
light and carry more energy. We wear sunglasses and sunblock to prevent damage
to our eyes and skin by ultraviolet rays.
Infrared rays are slightly longer waves than visible red light.
Although we cannot see infrared, we can feel it as heat. When heat energy is
transferred by radiation, it is carried by waves of infrared.
Radar is a way of locating aeroplanes and ships using a type of
radio waves called microwaves. These have much longer wavelengths than visible
light. Cooking is another use for microwaves.
Radio waves are the longest in the spectrum. They carry radio and
TV signals around Earth. Radio waves from outer space are picked up by radio
telescopes and used in studies of the universe.
When the energy stored in rock deep inside the Earth is
suddenly released, it travels up to the Earth’s surface in huge seismic
shock waves. The waves move along weaknesses in the rock known as faults. As
they do so, they produce violent shaking of the ground and an earthquake. The
largest earthquakes can release as much energy as a small atomic
bomb.
Earthquakes kill around 10,000 people every year worldwide.
Many cities now have buildings that absorb the energy in seismic waves. They
may wobble, but they do not collapse.
