2.07 Energy Conversions
Energy is defined as the ability to do work. Sometimes it’s easier to describe what energy does
that what energy is. That is because, unlike matter, energy is not something you can see or touch.
Energy is a property of matter, and all matter has it. Whenever a ligh bulb is lit, a turkey is
roasted, an orchestra plays, a fan spins, a book falls off the shelf, or a fire burns, you can be sure
that energy – in one form or another – made it happen.
Energy comes in many different forms. While it can be transferred from one object or system to
another or converted from one form to another, energy cannot be created or destroyed. This rule
is known as the Law of Conservation of Energy. The law simply states that energy cannot be
created or destroyed.
Mechinical energy is the energy an object has because of its motion or position. There are two
kinds of mechinical energy: kinetic and potential. Kinetic energy is the energy an object has
because it is moving. The greater the speed and mass of an object, the greaterits kinetic energy.
Potential energy is energy an object has because of its postion or shape.
Other forms of energy include the following:
Thermal energy(sometimes called heat energy) is the energy related to the temperature of a
substance or object.
Electromagnetic or Light energy is the energy carried by light and other kinds of
electromagnetic waves.
Chemical energy is the energy stored in chemical bonds.
Electrical energy is the energy produced by electric charges.
Nuclear energy is the energy contained in the nuclei of atoms.
Sound energy is the energy carried by sound waves.
Let’s look at some examples of energy being converted from one form to another.
Think about when you place a pot of water on the stove to boil. The electric energy that is being used to
turn the stove on is being converted to thermal energy (heat) then the heat is transferred to the pot
through conduction (remember that from 2.04?).
Have you ever stood close enough to a stero speaker to feel the sound coming out or to see the speaker
vibrate? What you are seeing and feeling is sound energy being converted to kinetic energy. Remember,
kinetic energy is the energy of motion. When you feel the vibrations of air, you are feeling the sound
energy being converted to kinetic mechanical energy because it is causing the air molecules to move.
You have probably seen solar panels on top of a house before. These solar panels, trap the
electromagnetic energy and thermal energy that is in the sun’s rays. When the panel trap’s this energy it
is converting it to stored chemical energy. When the house needs electricity, the stored chemical energy
in the solar panels is converted to electricity or electric energy.
Our bodies also store chemical energy in the form of fat. When we eat a salad for example, our bodies
are using the chemical energy that is stored in the plant (the plant got it’s energy from the sun).
Whatever is left over, our bodies store as potential chemical energy to use later. When we go for a run,
our muscle cells will convert the stored chemical energy to kinetic mechanical energy so that we can
move. Some of it is also converted to thermal energy, which is why we sweat!
Read this short story below and see how many energy conversions you can find:
Music has the power to energize!
You’re having a bad day! You just want a minute to yourself, so you walk to your
room. You sit on your bed, pick-up your MP3 player, put on the headphones and turn it
on. You hear the first few notes of your new favorite song, and a smile spreads across
your face. As the song plays, your foot starts to tap. Then you start to play the “air
drums”. Before you know it, you are dancing around your room. By the time the chorus
starts, you are singing at the top of your lungs. You’re getting hot, so you turn on the
fan. The umbrella in the corner catches your eye and you grab it for the big guitar solo!
The song comes to an end and you collapse on your bed. Then you think to yourself,
“What was I mad about again?”
Could you find at least 5 examples of energy conversions? Scroll down to see some that I found:
1. walk to your room; pick-up MP3 player, turn it on all represent chemical energy in body cells to
mechanical/kenetic energy
2. Turn on the MP3 player – stored chemical energy (also potential energy) to converted to electrical
energy
3. Electrical energy in the MP3 player is converted to sound energy heard in head phones.
4. Smiling and all the muscles used to dance and sing represent chemical energy in cells to
mechanical/kenetic energy
5. “getting hot” represents the mechanical energy in muscle movement converting to thermal energy
6. Turn on fan – electrical energy converted to mechanical energy
7. Singing mechanical energy in muscles is converted to sound energy
8. Umbrella sitting in corner has potential energy that is converted to kenetic (mechanical energy) as it
“becomes” an air guitar.
You should be ready to do your assessment for this lesson. If you have any questions, please contact
your teacher!
There is a small file to help you with this assignment. If you need it, ask your teacher where you can
find it!