Forms of energy in THE HUMAN BODY
Speaking and listening
Humans communicate using our voices, which make sound, and our
ears, which hear sound. Listening and hearing involve the transfer
and transformation of sound energy.
Where sound energy comes from
Sound waves are produced when particles in matter vibrate back
and forth. The vibration moves through matter in a wave. Sound
waves travel through the air to our ears and then to our brains,
where the vibrations are translated into the sounds we hear.
The sound waves of your
voice do not travel far
through the air. However,
when you talk on a
telephone, the sound
waves from your voice
are transformed into
electrical energy, which
can travel long distances.
How humans make sound
energy
Humans use their voices to sing, talk, shout,
whisper and hum. The sound of our voices is
produced in the larynx, or voice box, which is in
the throat.
The larynx contains folds of skin called vocal
cords. When you talk or sing, the force of air
moving from your lungs makes your vocal cords
vibrate, producing sounds. The kinetic energy of
moving air is transformed into sound energy.
Different sounds are produced by changing how
fast the air flows across the vocal cords or by
changing the shape of your mouth, tongue
and lips.
When a sound is made, sound waves travel out in a circle from
the source of the sound, like the ripples that form when a stone is
dropped in water.
Loud sounds make sound waves with more energy than soft
sounds. The distance that a sound travels depends on how loud it
is and what it is travelling through.
Sound waves
lose energy and become
weaker as they move away from
the source of the sound, just as
ripples get smaller as they travel
further away from a stone that
has been dropped into
a pond.
Sound energy
helps us talk to
our friends.
Try this
Put your fingers gently on the
front of your neck. Feel for
the hard lump that is your
larynx and start humming.
Can you feel the vibrations
through your fingertips?
Vocal cords
vibrate when
air moves past
them, creating
the sound of
your voice.
larynx
vocal cords
trachea
18
oesophagus
19
speaking and listening
Sound energy has loudness and pitch
How humans hear sound energy
Try this
Tie two pieces of string to a wire
coathanger. Wind one piece of string
around each forefinger and put them
in your ears so that the coathanger
hangs in front of you. Have someone
gently tap the coathanger with a
pencil. What can you hear?
Humans hear with their ears. Ears work by collecting waves of
sound energy travelling through the air around us and sending
them into the head through the ear canal. The sound waves hit
the eardrum, which is stretched tight like a drum across the end of
the ear canal, making it vibrate as well.
In turn, the vibrating eardrum sets off a chain of vibrations from
tiny ear bones in the middle ear to the cochlea in the inner ear.
The cochlea, which is filled with liquid, acts as a microphone and
transforms the vibrations into electrical signals. The electrical
signals are sent through nerves from the cochlea to the brain,
which interprets the signals as sound.
In the ear, sound energy is transformed
into kinetic energy in the eardrum.
Kinetic energy is transferred to the
cochlea, where it is transformed into
electrical energy and sent to the brain.
outer ear
The sounds humans hear vary in loudness and pitch, depending on
the shape of the sound wave.
Loudness
Loudness is how soft or how loud a sound is. It is measured on
a scale of decibels (dB), which starts at zero, the softest
sound a human can hear. Every increase of 10 dB along the
scale means that the sound is 10 times louder. An average
conversation is about 60 dB. A sound of 130 dB is painful to
our ears.
Although sound energy is
not as powerful as other
forms of energy, very loud
sounds, such as explosions,
can damage eardrums or
even break glass.
Pitch
Pitch is how high or low a sound
is and it depends on the speed of
the sound wave’s vibration. Pitch
is measured in hertz (Hz). One
hertz is one vibration per second.
High-pitched sounds are made
by faster vibrations and have
more energy than low-pitched
sounds. Humans can usually hear
sounds pitched from 20 Hz
to 20 000 Hz.
middle ear
inner ear
nerve
leading to
the brain
cochlea
ear canal
20
You hear music
when your ears transform
sound energy from an mp3 player
into electrical energy in your brain.
If the volume is too loud too often, the
nerves inside the central part of the ear
can be damaged. This means that the
sound waves will not be converted
into electrical signals properly,
affecting your hearing.
ear drum
21
Forms of energy in THE HUMAN BODY
How digestion works to provide energy
Fuelling the body
The chemical energy in food is released when we digest food. The
human body digests food to obtain nutrients and energy, while
getting rid of waste.
Human bodies need a constant supply of energy to grow, move
and survive. We get energy by eating food, which contains stored
chemical energy. Our bodies extract energy from the food we eat
through the process of digestion.
Food is a source of chemical energy
Linus Pauling
(1901–1994)
Linus Pauling
was an American
chemist. He
received the
Nobel Prize for
Chemistry in
1954 for his
research on the
chemical bonds
that join atoms
together to form
molecules.
The food we eat is made of molecules, which are held together
by bonds. Different molecules store different amounts of chemical
energy in their bonds.
Our bodies digest food through a series of chemical reactions.
During these chemical reactions, molecules break apart and new
molecules are formed.
The new molecules sometimes need less chemical energy to bind
them together than the original molecules. Some chemical energy
is left over and can be transformed into other forms of energy,
such as heat energy and kinetic energy.
Digestion begins in the mouth. Teeth break up food into smaller
pieces and saliva, or spit, starts the chemical breakdown of
food. When you swallow, food enters the oesophagus, where
the force of gravity and strong muscle movements combine to
squeeze the food down to the stomach.
In the stomach, the food is mashed up and mixed with digestive
juices to form a sloppy mixture. The mixture is sent to the small
intestine, which breaks it down even further. The small intestine
absorbs the nutrients from the food and sends them through the
bloodstream to the liver.
The liver is like a chemical processing
factory. It uses the nutrients to make
products that can be easily used
by the body and also filters out
harmful substances.
salivary glands
Humans produce
about 1.7 litres of
saliva every day as they
digest their food.
As food
travels through your
digestive system, it is
broken down into smaller
parts that your body uses
to build your cells and
to provide energy.
tongue
glucose
oesophagus
liver
Scientist Snapshot
stomach
Most food contains a sugar called
glucose, which is made of carbon,
oxygen and hydrogen atoms joined
together by chemical bonds. These
bonds store chemical energy that
our bodies use as a fuel.
22
hydrogen atom
carbon atom
oxygen atom
small intestine
large intestine
23