Energy Systems
UNIT 7
Student Reader
Front Cover:
The cover shows a photograph of a sled that is not in motion. The movement of a sled from one place to another is an example of a
mechanical energy system. A push or the pull of gravity inputs energy into the sled. The movement of the sled is the output energy. The sled stops moving due to friction between the bottom of the sled and the ground.
Unit 7:
Energy Systems
Table of Contents
Section 1: Forces 4
What Powers a Sled? 4
Where Does Energy Come From? 6
In the Know: Forms of Energy 7
What Is Friction? 8
Section 1: Try This on Your Own 9
Section 2: Electromagnetic Motor 10
Where Are Energy Systems Found? 10
How Do Magnets Work? 11
What Is a Motor? 12
Electromagnetic Motor Activity Sheet
13 Section 2: Try This on Your Own 14
Glossary 15
Main Ideas
Energy is a force that is able to do work. There are several forms of energy.
Energy is never created or destroyed; it constantly changes forms as it moves through energy systems.
Friction is the transfer of mechanical energy to heat energy that takes place when two moving objects or substances rub against each other.
What Powers a Sled?
A s a boy, Lance Mackey
dreamed of winning the Iditarod Trail Sled Dog Race. It’s not an easy task. The roughly 1,900 kilometer race across the
Alaskan wilderness can take 8 to 20 days. Racers may face
blizzards and sub-zero temperatures. Lance
watched his father and older brother both win, and it was his turn to carry on the family legacy.
Lance overcame many hardships to train for the race, but that didn’t stop him from winning first place in 2007, 2008, 2009, and 2010.
1 Forces
Lance’s victories weren’t just chance. It takes strategy to win a sled race. A dog sled racer must know about forces before he or she can race.
An Iditarod race allows each musher (racer) to
train a team of 12 to 16 dogs. Lance needed to train his dogs until they were strong enough to cross many kilometers of icy roads. He also needed to use a sled that was light enough for his dogs to pull.
Racers usually train dogs called huskies.
The Iditarod can last many days, so it is important that the racer and his dogs take breaks. Dogs need energy to pull the sled for such a long distance.
They need to be fed at least 10,000 calories a day, with a diet that may include lamb, chicken, beef, moose, or salmon.
The dogs need all this energy because it takes a great amount of force to pull a grown adult like Lance, as well as his supplies, especially at a speed fast enough to win a race.
Mushers know that the more mass something has, the more force is needed to move an object across any distance. The Iditarod has rules about how many dogs can pull a racer to make the race fair. A team of 30 sled dogs would be able to move much faster than a team of 6 sled dogs.
energy – a force that is able to do work (e.g., move an object, heat up an object,
charge an
object)
force – the
energy (or
effort) needed
to do work
Where Does Energy Come From?
D ogs can pull sleds because their bodies, like all animals, transfer the chemical energy in food into mechanical energy to move. A dog is an example of an energy system because there is an energy input (food) and an energy output (movement).
According to the law of conservation of energy, energy cannot be created or destroyed; it can only be transferred from one form to another. Energy is always either being stored or doing work.
Potential energy is energy that is being stored. A stretched archer’s bow is an example of potential energy. The more the archer pulls back the bow, the farther the arrow will travel. Another example is a bicycle at the top of a hill. The higher the rider is on the hill, the farther the bicycle will travel once it goes over the hill.
The energy of a moving arrow or bicycle is called kinetic energy. Kinetic energy is energy in
motion. The more kinetic energy something has, the more work it can do.
energy system – a set of
connected parts that transfers an input of energy to a different output of energy
conservation of energy – a physical law that states that energy cannot be created or destroyed; it can only be transferred from one form to another
kinetic energy kinetic energy
energy in energy out
potential energy
In the Know: Forms of Energy
Forms of Potential Energy Forms of Kinetic Energy
chemical: energy stored in the bonds of atoms
and molecules (e.g., food, wood, gasoline)
heat: the motion of atoms and molecules in a substance or
object as its temperature increases (e.g., boiling water)
gravitational:
stored energy related to an object’s height above the ground (e.g., a roller coaster at the top of the track)
sound: energy produced by sound vibrations moving through a
substance in waves (e.g., music, talking)
nuclear:energy stored in the nucleus of an atom (e.g., energy that holds the nucleus together)
light:the movement of energy in a wave- like pattern that
comes from light (e.g., visible light, X-rays) elastic:energy stored in
objects when stretched (e.g., compressed springs, stretched rubber bands)
mechanical:the energy of a
substance or system due to its motion (e.g., car moving, windmill blades turning)
static electricity:
energy stored in an electric charge (e.g., static charged
balloons)
current
electricity: the movement of charged particles through a
conductor (e.g., electricity, lightning)
