Download Potential Energy - 7sciencewithmcmillan

Forms of Energy
Energy is the ability to do work. It is one of the fundamental building blocks of the universe.
Since energy is the ability to do work, and work is the product of a force over the distance it acts, energy can be
understood as the ability to cause a force to act over a certain distance.
Energy is a necessary component of everything in the universe. Every event that takes place, from the formation of
stars to the operation of machines, involves energy that is flowing from one place to another and changing back and
forth from one form to another. Energy flows via waves. The different forms of energy include:
 kinetic

potential

mechanical

radiant (light)

thermal

sound

electrical
In some ways, kinetic and potential energy can be thought of as the two fundamental types of energy. Kinetic
energy is the energy of motion, and potential energy is stored energy. All other forms of energy contain aspects of
kinetic and/or potential energy.
Kinetic Energy
Kinetic energy is the energy that an object has due to its motion. Kinetic energy is present in all moving objects such
as:

a moving car

blowing wind

a sliding sled

flowing water

a moving ball

a spinning amusement park ride
All moving objects have kinetic energy.
Kinetic energy can be harnessed and transformed into other kinds of energy. Humans routinely transform kinetic
energy into electrical energy by using the energy of flowing water in hydroelectric dams, blowing wind in wind
turbines, and rising steam in other power plants.
The amount of kinetic energy an object has is related to its mass and velocity. The greater the velocity and mass of an
object, the more kinetic energy it has.For example, if a car, a van, and a bus were moving at the same speed, the bus
would have the most kinetic energy because it has the most mass.
Potential Energy
Potential energy is defined as stored energy. Energy is stored by doing work against a force. Potential energy comes in
many different forms including:
 elastic potential energy

gravitational potential energy

chemical potential energy
Potential energy that results from stretching or compressing an object is called elastic potential energy. For example,
when a spring is stretched, work has been done to deform the spring, resulting in increased potential energy. When
the spring is released, the potential energy will be transformed to kinetic energy as the spring snaps back into its
original shape. This is also true of a spring that is compressed.
Stretched or compressed objects store elastic potential energy.
Potential energy that is related to an object's height above the ground is known as gravitational potential
energy. Generally, an object's gravitational potential energy is directly proportional to the object's mass, height, and
the acceleration due to gravity. When two object's masses are equal, the object with the greater height has the
greater gravitational potential energy.
The bungee jumper in this picture has gravitational potential energy due to his height. As he falls, it is transformed
into kinetic energy.
Chemical potential energy is the energy that is stored
in the bonds and attractions within and between the
atoms that make up molecules. When a substance
undergoes a chemical reaction, chemical potential
energy is released.
Chemical potential energy is the type of energy that
humans and other organisms get out of food. The food
we eat contains stored chemical energy, and oxidation
of the food through cellular respiration releases this
energy for use in our bodies. Different substances
contain different amounts of chemical energy; in other
words, some substances are more likely than others to undergo chemical changes.
Substances that can be burned, such as fossil fuels and wood, also contain chemical potential energy. So when coal,
oil, wood, or natural gas are burned, their chemical potential energy is released.
Substances contain chemical potential energy due to the bonds between their atoms and molecules. Chemical
reactions, such as burning, can release this energy.
Hydrogen fuel and batteries also contain chemical potential energy. These technologies are often called energy
carriers since they can be used to store energy and transport it to new locations.
Mechanical Energy
Mechanical energy is best understood as the sum of an object's kinetic energy and potential energy. So it is the total
amount of energy that an object has due to its position, orientation (if it's stretched or compressed), and its motion.
A skateboarder on a ramp, for example, has kinetic energy due to his motion, but he also has gravitational potential
energy every time he leaves the ground. Both of these values change as he moves up and down a ramp, but his
mechanical energy (potential + kinetic) does not change.
A skateboarder loses kinetic energy and gains potential
energy as he moves up a ramp. But his mechanical energy
remains constant.Objects with mechanical energy are able
to do work, and mechanical energy is the form of energy
involved in the operation of simple machines. For example,
if a person lifts an axe above his head, he gives the axe
potential energy because the axe is now above the
ground. The person had to use kinetic energy to lift the axe.
As the person brings the axe down, he is still using kinetic
energy, and the energy of the axe is changed into kinetic
energy because it is now in motion. When the axe strikes a
piece of wood, it can transfer some of its energy to the wood, doing work on the wood and causing two portions of
wood to move away from each other.
Radiant Energy (Light)
Radiant energy is energy that is transmitted in the form of electromagnetic waves. Because of this, radiant energy
does not need a medium to travel through. Examples of radiant energy include visible light and infrared light, which
can come from the Sun. Numerous human-made objects also emit radiant energy, including light bulbs and street
lights. Radiant energy is carried by electromagnetic waves. These waves can include visible light, infrared light, x-rays,
gamma rays, and radio waves. Humans harness radiant energy from the Sun (solar energy) to generate electricity
using solar cells and power stations.
Thermal Energy
Thermal energy is the energy of an object due to the random motion of its particles. The faster the particles move,
the greater the thermal energy, and the greater the temperature. Temperature can be used as an indicator of the
amount of thermal energy that an object possesses, but it is not the same as thermal energy. Heat is thermal energy
that is transferred from warmer objects to colder objects. Heat energy can be produced from matter that undergoes a
chemical change or from another form of energy. Heat is an important ingredient in the production of electricity at
power plants. It can be used to boil water and produce steam, which can create pressure and cause the blades of a
turbine to turn. Steam is water that is in the gaseous state. Since water expands when it changes from a liquid to a
gas, it creates pressure that can turn against the fan blades of a turbine and cause the turbine to turn.
Sound Energy
Sound energy is the form of energy that is carried by sound waves as they travel through a medium, such as
air. Sound waves are produced by vibrating objects and travel through various materials. The vibrating of a drum
produces sound waves that travel through the air. These waves carry sound energy. The speed of a sound wave
depends on what the wave is traveling through. Sound travels more quickly through more elastic substances. Water,
for example, carries sound waves more rapidly than air. Sound waves cannot travel through a vacuum such as outer
space because there is no material for the waves to travel through.
Electrical Energy
Electrical energy is the energy associated with charged particles, such as electrons. When these particles are moving
or flowing in a current, this kind of energy is also referred to as electricity. Electricity travels through conducting
materials, such as wires. Lightning is an example of electrical energy in nature. Electrical energy is an incredibly useful
form of energy because it can be generated from many other types of energy and easily transported to new
locations. Once it is generated, electrical energy can be transformed into heat, light, sound, or mechanical energy. For
this reason, electricity is sometimes called an energy carrier.
Electrical energy is the energy associated with charged particles—usually electrons. Humans commonly carry energy
over long distances using electricity. Electricity is easily transformed into other forms of energy. Batteries, solar cells,
generators, flowing water, moving air, and burning fossil fuels can all be used to produce electrical energy. However,
it is important to note that energy cannot be created or destroyed. It only changes form. So the electrical energy
produced from any of the sources above originated as a different form of energy somewhere else.
Energy Resources
Numerous natural resources are used by human societies to generate energy (particularly electrical energy). There are
many different ways of obtaining, transforming, and distributing this energy, each of which has different environmental
consequences.
Fossil Fuels
The most common method for obtaining energy is through the burning of fossil fuels, such as coal, oil, and natural
gas. These fuels can be converted to other forms of energy in many ways, including the production of electricity
through coal-burning power plants. Fossil fuels are abundant and cheap, and coal-burning power plants are currently
the most effective way for generating widespread electricity where and when it is needed. However, coal-fired power
plants cause large amounts of pollution and can affect the Earth's natural greenhouse effect. Also, fossil fuels are
nonrenewable resources, so humans will eventually run out of them at current rates of usage.
Power plants like this one burn coal in order to produce electricity. While coal is plentiful and cheap, it produces a lot
of air pollution. Measures are being taken to reduce the amount of pollution released by coal burning, but it is
impossible to completely eliminate it.
Solar Energy
Solar energy is an inexhaustible resource, which means humans cannot
use it all up, and it a type of green energy—it has far fewer
environmental consequences than fossil fuels. The primary negative
effects are minor and are related to the manufacturing and disposing of
solar panels, which are used to convert solar energy into electrical
energy. The main reason that solar energy technology is not more
widespread at this time is that it is very expensive to harness solar energy
in useful quantities. Solar energy is also not as reliable as energy derived
from fossil fuels, because it is not always sunny. Not all locations can utilize solar technologies either. While California
and Colorado might be excellent places for solar power plants, Wisconsin and Michigan might not be. But as the
technology continues to improve, solar energy costs decrease, and more solar panels are being used.
Solar energy can be harnessed using solar panels such as this one. While this process results in far less pollution or waste
than burning fossil fuels, it is currently very expensive and therefore not yet used widely across the world.
Wind Energy
Wind energy is an inexhaustible resource that comes from the
movement of air heated by the Sun. Wind energy is also a form of
green energy. As with solar energy, wind energy has very few
negative environmental consequences, and these are mostly related
to the manufacture and disposal of wind turbines. However, wind
turbines also pose hazards for birds and bats. Unlike solar energy
technologies, wind technologies are relatively inexpensive. In terms
of electricity prices, wind energy is able to compete with fossil-fuel
generated electricity, but there are limitations to wind as well. The
inconsistency of wind patterns is one of the challenges facing the expansion of wind power. It is not always easy to
predict when and where the wind will be blowing. And there is not enough wind in many locations to generate
electricity. It is estimated that the U.S. has enough wind to supply about 20% of its current electricity demand, if wind
energy is used to its full potential.
Wind turbines like these are used to convert blowing wind energy into electricity. This process offers a much cleaner
alternative to burning fossil fuels, but not every location is suitable for wind power. And wind power is unreliable,
since the wind does not blow in consistent patterns.
Hydroelectric Energy
Hydroelectric energy is electrical energy converted from the kinetic energy of falling water. It is an inexhaustible
resource. Like solar and wind power, hydroelectricity is considered to be a green energy. Humans have constructed
dams in many parts of the world to hold back rivers. The held-back water is then released through tunnels in the dam
to spin turbines that run generators (see figure below). Hydroelectric energy is much cleaner than fossil fuels, but the
construction of dams is extremely disruptive to natural
ecosystems, especially where it prevents fish and other
aquatic animals from moving up or down a
river. Hydroelectric energy can also be harnessed from
the motion of tidal waters, but such examples are not
as common as those that use river dams.
Diagram of a hydroelectric dam. The main
environmental drawback of dams like these is their
disruption of river ecosystems.
Energy Transformations
Energy can be transformed, or changed, from one form to another.
Energy can change forms as it travels through an object, material, or system.Types of energy transformations can
include:

change from chemical energy to radiant, acoustic, or electrical energy

change from kinetic energy to potential energy

change from nuclear energy to light, chemical, or mechanical energy

change from almost any other form of energy to heat energy
Energy transformation diagrams are sometimes used to show how energy is changed as it is transferred from place to
place.
Transformation of Chemical Energy
Chemical energy is energy that an object or material has because of the bonds, or attractions, holding the particles of
the material together. Batteries contain chemical energy. Fossil fuels contain chemical energy that is released when
the fuels are burned. Food contains chemical energy that is released by our bodies and used to perform life
processes. Some common transformations of chemical energy are shown in the energy transformation diagrams
below.
Transformation between Kinetic Energy & Potential Energy
Kinetic energy is the energy something has because of its motion. Potential energy is the
energy something has because of its position. As objects or organisms move, they may gain
potential energy and lose kinetic energy, or they may gain kinetic energy and lose potential
energy.
For example, the total amount of energy in this yo-yo stays the same at all times, but the
amount of kinetic and potential energy changes with the position of the yo-yo. When the yoyo is at its highest position (before it falls), all of its energy is in the form of potential energy.
As the yo-yo falls, the potential energy is transformed into kinetic energy because it is moving. When the yo-yo goes
back up, the kinetic energy is transformed back into potential energy again.
Electric Energy Transformations
Electric energy is the energy associated with moving electric charges. It is an
extremely useful form of energy, since it is easily generated from other forms of
energy, easily transported, easily distributed, and easily transformed into other forms
of energy.
Many household items transform electric energy (in the form of electricity) into other
types of energy. Some examples include the following:
 Ceiling fans transform electric energy into kinetic energy.

Toasters, electric heaters, and electric stoves transform electric energy into
thermal energy.

Televisions transform electric energy into sound energy and light (radiant) energy.
Electric energy can also be stored in batteries (as chemical potential energy) and in
generators (often as elastic potential energy).
Once generated, electric energy is can be distributed easily along power lines.
Transformation of the Sun's Nuclear Energy
Nuclear energy is produced through fusion reactions taking
place inside the Sun. Nuclear energy is converted into
radiant energy (light and other forms of electromagnetic
radiation) that travels through space. Radiant energy is
absorbed by the atmosphere and converted into heat
energy.
Plants are able to convert radiant energy from the Sun into
chemical energy, stored in the food created by
photosynthesis. When consumers, such as humans, eat
plants, the chemical energy is converted into mechanical and heat energy.
Heat and Energy Transformations
Regardless of the type of transformation, essentially all of these transformations have something in common—some
of the energy involved is transformed to heat. Some of the energy of an exploding star, for example, radiates through
space as heat. Some of the stored chemical energy in the human body converts to heat when it is released to help
grow new living cells or to make the body move. Energy can also be lost as heat during transfer of the same type of
energy. For example, the moving gears of a machine lose heat energy due to friction as mechanical motion is
transferred from one gear to another.
The man in the picture above is transforming stored chemical energy in his body to make his legs pedal the
bicycle. During this transformation, some of the energy is lost as heat. Also, some of the mechanical energy he is
putting into the bike is lost as heat due to friction between the bike's gears.
Conservation of Energy
The Law of Conservation of Energy states that the total amount of energy in a system remains constant. Energy can be
converted from one form to another, but it cannot be created or destroyed.
The total amount of energy in the universe is a constant. Energy can:
o move from one object to another, such as when a moving pool cue strikes another ball, causing it to move.
o
change from one kind or form of energy to another, such as when energy changes from potential to kinetic or vice
versa, or when electric energy is changed to kinetic energy in an electric fan.
o
or some combination of these two.
Energy Transformation
When energy changes from one form to another, the process is known as energy transformation. Examples include:
o the potential energy of elevated objects being converted to kinetic energy as they fall, roll, or slide downward
o
the chemical potential energy of a battery changing to the kinetic electrical energy of moving electrons in a current
in electrical devices
o
the chemical energy of wood changing to heat and light energy as it burns
Conservative forces are those that can change energy from potential to kinetic or vice versa with perfect efficiency—
that is, all of the kinetic energy becomes potential energy, and all of the potential energy becomes kinetic.
Conservative forces include gravity, the spring force, and the electromagnetic force. When non-conservative forces
act to transform energy, some of the energy is changed into heat. This energy may sometimes be said to be "lost"
through heat dissipation because it cannot all be used to do work. Because energy is always conserved, energy that is
transformed into heat is not destroyed but is unusable, or it might travel out of the system by radiation, conduction,
or convection.
Example
Brenda turns on a small flashlight and forgets to turn it off.
The flashlight stays on until the chemical energy in the batteries is used up. If no
energy is lost as heat, how much of the chemical energy from the batteries is
transformed into light energy?
Answer: all of it. Energy cannot be created or destroyed; it can only change form. In a real flashlight, all of the
chemical energy is transformed into heat and light after first being transformed into electrical energy. In this situation,
since no heat is produced, all of the energy is eventually transformed into light.