Transcript Conceptual Physics - Southwest High School

Chapter Nine Notes:
Energy
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In the past several chapters, we utilized Newton's laws to analyze
the motion of objects. Force and mass information were used to
determine the acceleration of an object. Acceleration information
was subsequently used to determine information about the velocity
or displacement of an object after a given period of time. In this
manner, Newton's laws serve as a useful model for analyzing motion
and making predictions about the final state of an object's motion.
In this unit, an entirely different model will be used to analyze the
motion of objects. Motion will be approached from the perspective
of work and energy. The affect that work has upon the energy of an
object (or system of objects) will be investigated; the resulting
velocity and/or height of the object can then be predicted from
energy information. In order to understand this work-energy
approach to the analysis of motion, it is important to first have a
solid understanding of a few basic terms. Thus, the sections of this
unit will focus on the definitions and meanings of such terms as
work, mechanical energy, potential energy, kinetic energy, and
power.
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When a force acts upon an object to cause a displacement of the
object, it is said that work was done upon the object. There are
three key ingredients to work - force, displacement, and cause. In
order for a force to qualify as having done work on an object, there
must be a displacement and the force must cause the displacement.
There are several good examples of work which can be observed in
everyday life - a horse pulling a plow through the field, a father
pushing a grocery cart down the aisle of a grocery store, a freshman
lifting a backpack full of books upon her shoulder, a weightlifter
lifting a barbell above his head, an Olympian launching the shotput, etc. In each case described here there is a force exerted upon
an object to cause that object to be displaced.
Mathematically, work can be expressed by the following equation.
where F is the force, d is the displacement, and the angle (theta) is
defined as the angle between the force and the displacement vector.
Perhaps the most difficult aspect of the above equation is the angle
"theta." The angle is not just any 'ole angle, but rather a very specific
angle. The angle measure is defined as the angle between the force
and the displacement. To gather an idea of its meaning, consider the
following three scenarios.
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Scenario A: A force acts rightward
upon an object as it is displaced
rightward. In such an instance, the
force vector and the displacement
vector are in the same direction. Thus,
the angle between F and d is 0
degrees.
Scenario B: A force acts leftward upon
an object which is displaced rightward.
In such an instance, the force vector
and the displacement vector are in the
opposite direction. Thus, the angle
between F and d is 180 degrees.
Scenario C: A force acts upward on an
object as it is displaced rightward. In
such an instance, the force vector and
the displacement vector are at right
angles to each other. Thus, the angle
between F and d is 90 degrees.
Units of Work
Whenever a new quantity is introduced in physics, the standard
metric units associated with that quantity are discussed. In the case
of work (and also energy), the standard metric unit is the Joule
(abbreviated J). One Joule is equivalent to one Newton of force
causing a displacement of one meter. In other words,
 The Joule is the unit of work.
 1 Joule = 1 Newton * 1 meter
 1 J = 1 N * m
In fact, any unit of force times any unit of displacement is equivalent
to a unit of work. Some nonstandard units for work are shown
below. Notice that when analyzed, each set of units is equivalent to
a force unit times a displacement unit.
In summary, work is done when a force acts upon an object to cause
a displacement. Three quantities must be known in order to
calculate the amount of work. Those three quantities are force,
displacement and the angle between the force and the displacement.
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Power
The quantity work has to do with a force causing a displacement.
Work has nothing to do with the amount of time that this force acts
to cause the displacement. Sometimes, the work is done very quickly
and other times the work is done rather slowly. For example, a rock
climber takes an abnormally long time to elevate her body up a few
meters along the side of a cliff. On the other hand, a trail hiker (who
selects the easier path up the mountain) might elevate her body a
few meters in a short amount of time. The two people might do the
same amount of work, yet the hiker does the work in considerably
less time than the rock climber. The quantity which has to do with
the rate at which a certain amount of work is done is known as the
power. The hiker has a greater power rating than the rock climber.
Power is the rate at which work is done. It is the work/time ratio.
Mathematically, it is computed using the following equation.
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The standard metric unit of power is the Watt.
As is implied by the equation for power, a unit
of power is equivalent to a unit of work divided
by a unit of time. Thus, a Watt is equivalent to a
Joule/second. For historical reasons, the
horsepower is occasionally used to describe the
power delivered by a machine. One horsepower
is equivalent to approximately 750 Watts.
Most machines are designed and built to do work on objects. All machines
are typically described by a power rating. The power rating indicates the rate at
which that machine can do work upon other objects. Thus, the power of a
machine is the work/time ratio for that particular machine. A car engine is an
example of a machine which is given a power rating. The power rating relates to
how rapidly the car can accelerate the car. Suppose that a 40-horsepower
engine could accelerate the car from 0 mi/hr to 60 mi/hr in 16 seconds. If
this were the case, then a car with four times the horsepower could do the same
amount of work in one-fourth the time. That is, a 160-horsepower engine could
accelerate the same car from 0 mi/hr to 60 mi/hr in 4 seconds. The point is
that for the same amount of work, power and time are inversely
proportional. The power equation suggests that a more powerful engine can do
the same amount of work in less time.
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A person is also a machine which has a power rating. Some people
are more power-full than others. That is, some people are capable
of doing the same amount of work in less time or more work in the
same amount of time. A common physics lab involves quickly
climbing a flight of stairs and using mass, height and time
information to determine a student's personal power. Despite the
diagonal motion along the staircase, it is often assumed that the
horizontal motion is constant and all the force from the steps are
used to elevate the student upward at a constant speed. Thus, the
weight of the student is equal to the force which does the work on
the student and the height of the staircase is the upward
displacement. Suppose that Ben Pumpiniron elevates his 80-kg body
up the 2.0 meter stairwell in 1.8 seconds. If this were the case, then
we could calculate Ben's power rating. It can be assumed that Ben
must apply a 800-Newton downward force upon the stairs to elevate
his body. By so doing, the stairs would push upward on Ben's body
with just enough force to lift his body up the stairs. It can also be
assumed that the angle between the force of the stairs on Ben and
Ben's displacement is 0 degrees. With these two approximations,
Ben's power rating could be determined as shown below.
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Ben's power rating is 871 Watts. He is quite a horse.
The expression for power is work/time. And since the expression
work is force*displacement, the expression for power can
rewritten as (force*displacement)/time. Since the expression
velocity is displacement/time, the expression for power can
rewritten once more as force*velocity. This is shown below.
for
be
for
be
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This new equation for power reveals that a
powerful machine is both strong (big force) and
fast (big velocity). A powerful car engine is strong
and fast. A powerful piece of farm equipment is
strong and fast. A powerful weightlifter is strong
and fast. A powerful linemen on a football team
is strong and fast. A machine which is strong
enough to apply a big force to cause a
displacement in a small mount of time (i.e., a big
velocity) is a powerful machine.
Mechanical Energy
Previously, it was said that work is done upon an object whenever a force
acts upon it to cause it to be displaced. Work is a force acting upon an
object to cause a displacement. In all instances in which work is done, there
is an object which supplies the force in order to do the work. If a World
Civilization book is lifted to the top shelf of a student locker, then the
student supplies the force to do the work on the book. If a plow is displaced
across a field, then some form of farm equipment (usually a tractor or a
horse) supplies the force to do the work on the plow. If a pitcher winds up
and accelerates a baseball towards home plate, then the pitcher supplies
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the force to do the work on the baseball. If a roller coaster car is
displaced from ground level to the top of the first drop of a roller
coaster ride, then a chain driven by a motor supplies the force to do the
work on the car. If a barbell is displaced from ground level to a height
above a weightlifter's head, then the weightlifter is supplying a force to
do work on the barbell. In all instances, an object which possesses
some form of energy supplies the force to do the work. In the instances
described here, the objects doing the work (a student, a tractor, a
pitcher, a motor/chain) possess chemical potential energy stored in
food or fuel which is transformed into work. In the process of doing
work, the object which is doing the work exchanges energy with the
object upon which the work is done. When the work is done upon the
object, that object gains energy. The energy acquired by the objects
upon which work is done is known as mechanical energy.
Mechanical energy is the energy which is possessed by an object due to
its motion or due to its position. Mechanical energy can be either kinetic
energy (energy of motion) or potential energy (stored energy of
position). Objects have mechanical energy if they are in motion and/or
if they are at some position relative to a zero potential energy position
(for example, a brick held at a vertical position above the ground or
zero height position). A moving car possesses mechanical energy due to
its motion (kinetic energy).
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A moving baseball possesses mechanical energy due to both its high
speed (kinetic energy) and its vertical position above the ground
(gravitational potential energy). A World Civilization book at rest on
the top shelf of a locker possesses mechanical energy due to its
vertical position above the ground (gravitational potential energy). A
barbell lifted high above a weightlifter's head possesses mechanical
energy due to its vertical position above the ground (gravitational
potential energy). A drawn bow possesses mechanical energy due to
its stretched position (elastic potential energy).
An object can store energy as the result of its position. For example, the
heavy heavy ball of a demolition machine is storing energy when it is held
at an elevated position. This stored energy of position is referred to as
potential energy. Similarly, a drawn bow is able to store energy as the result
of its position. When assuming its usual position (i.e., when not drawn),
there is no energy stored in the bow. Yet when its position is altered from its
usual equilibrium position, the bow is able to store energy by virtue of its
position. This stored energy of position is referred to as potential energy.
Potential energy is the stored energy of position possessed by an object.
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Elastic Potential Energy
The first form of potential energy which we will discuss is elastic
potential energy. Elastic potential energy is the energy stored in
elastic materials as the result of their stretching or compressing.
Elastic potential energy can be stored in rubber bands, bungee
chords, trampolines, springs, an arrow drawn into a bow, etc. The
amount of elastic potential energy stored in such a device is related
to the amount of stretch of the device - the more stretch, the more
stored energy.
Springs are a special instance of a device which can store elastic
potential energy due to either compression or stretching. A force is
required to compress a spring; the more compression there is, the
more force which is required to compress it further. For certain
springs, the amount of force is directly proportional to the amount
of stretch or compression (x); the constant of proportionality is
known as the spring constant (k).
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Such springs are said to follow Hooke's Law. If a spring is not
stretched or compressed, then there is no elastic potential energy
stored in it. The spring is said to be at its equilibrium position. The
equilibrium position is the position that the spring naturally
assumes when there is no force applied to it. In terms of potential
energy, the equilibrium position could be called the zero-potential
energy position. There is a special equation for springs which relates
the amount of elastic potential energy to the amount of stretch (or
compression) and the spring constant. The equation is
To summarize, potential energy is the energy which is stored in an
object due to its position relative to some zero position. An object
possesses elastic potential energy if it is at a position on an elastic
medium other than the equilibrium position.
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Chemical Potential Energy
The chemical energy in fuels is also potential energy. Any substance
that can do work through chemical reactions possesses chemical
energy. Potential energy is found in fossil fuels, electric batteries,
and the food we eat.
Gravitational Potential Energy
The first form of potential energy which we will discuss is
gravitational potential energy. Gravitational potential energy is the
energy stored in an object as the result of its vertical position or
height. The energy is stored as the result of the gravitational
attraction of the Earth for the object. The gravitational potential
energy of the massive ball of a demolition machine is dependent on
two variables - the mass of the ball and the height to which it is
raised. There is a direct relation between gravitational potential
energy and the mass of an object. More massive objects have
greater gravitational potential energy. There is also a direct relation
between gravitational potential energy and the height of an object.
The higher that an object is elevated, the greater the gravitational
potential energy. These relationships are expressed by the following
equation:
PEgrav = mass * g * height
 PEgrav = m * g * h
In the above equation, m represents the mass of the object, h
represents the height of the object and g represents the acceleration
of gravity (9.8 m/s/s on Earth).
To determine the gravitational potential energy of an object, a zero
height position must first be arbitrarily assigned. Typically, the
ground is considered to be a position of zero height. But this is
merely an arbitrarily assigned position which most people agree
upon. Since many of our labs are done on tabletops, it is often
customary to assign the tabletop to be the zero height position.
Again this is merely arbitrary. If the tabletop is the zero position,
then the potential energy of an object is based upon its height
relative to the tabletop. For example, a pendulum bob swinging to
and from above the table top has a potential energy which can be
measured based on its height above the tabletop. By measuring the
mass of the bob and the height of the bob above the tabletop, the
potential energy of the bob can be determined.
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Since the gravitational potential energy of an object is directly
proportional to its height above the zero position, a doubling of the
height will result in a doubling of the gravitational potential energy.
A tripling of the height will result in a tripling of the gravitational
potential energy.
Use this principle to determine the blanks in the following diagram.
Knowing that the potential energy at the top of the tall platform is
50 J, what is the potential energy at the other positions shown on
the stair steps and the incline?
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Kinetic energy is the energy of motion. An object which has motion whether it be vertical or horizontal motion - has kinetic energy.
There are many forms of kinetic energy - vibrational (the energy due
to vibrational motion), rotational (the energy due to rotational
motion), and translational (the energy due to motion from one
location to another). To keep matters simple, we will focus upon
translational kinetic energy. The amount of translational kinetic
energy (from here on, the phrase kinetic energy will refer to
translational kinetic energy) which an object has depends upon two
variables: the mass (m) of the object and the speed (v) of the object.
The following equation is used to represent the kinetic energy (KE)
of an object.
where m = mass of object
v = speed of object
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This equation reveals that the kinetic energy of an object is directly
proportional to the square of its speed. That means that for a
twofold increase in speed, the kinetic energy will increase by a factor
of four. For a threefold increase in speed, the kinetic energy will
increase by a factor of nine. And for a fourfold increase in speed, the
kinetic energy will increase by a factor of sixteen. The kinetic energy
is dependent upon the square of the speed. As it is often said, an
equation is not merely a recipe for algebraic problem-solving, but
also a guide to thinking about the relationship between quantities.
Kinetic energy is a scalar quantity; it does not have a direction.
Unlike velocity, acceleration, force, and momentum, the kinetic
energy of an object is completely described by magnitude alone.
Like work and potential energy, the standard metric unit of
measurement for kinetic energy is the Joule. As might be implied by
the above equation, 1 Joule is equivalent to 1 kg*(m/s)^2.
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Internal vs. External Forces
There are a variety of ways to categorize all the types of forces. Earlier
it was mentioned that all the types of forces can be categorized as
contact forces or as action-at-a-distance forces. Whether a force was
categorized as an action-at-a-distance force was dependent upon
whether or not that type of force could exist even when the objects
were not physically touching. The force of gravity, electrical forces,
and magnetic forces were examples of forces which could exist
between two objects even when they are not physically touching. In
this lesson, we will learn how to categorize forces based upon
whether or not their presence is capable of changing an object's total
mechanical energy. We will learn that there are certain types of forces,
which when present and when involved in doing work on objects will
change the total mechanical energy of the object. And there are other
types of forces which can never change the total mechanical energy of
an object, but rather can only transform the energy of an object from
potential energy to kinetic energy (or vice versa). The two categories
of forces are referred to as internal forces and external forces.
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Forces can be categorized as internal forces or external forces.
There are many sophisticated and worthy ways of explaining and
distinguishing between internal and external forces. Many of these
ways are commonly discussed at great length in physics textbooks.
For our purposes, we will simply say that external forces include the
applied force, normal force, tension force, friction force, and air
resistance force. And for our purposes, the internal forces include
the gravity forces, magnetic force, electrical force, and spring force.
Internal Forces
External Forces
Fgrav
Fspring
Fapp
Ffrict
Fair
Ftens
Fnorm
F magnetic
F electric
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The importance of categorizing a force as being either internal or
external is related to the ability of that type of force to change an
object's total mechanical energy when it does work upon an object.
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When net work is done upon an object by an external force, the total
mechanical energy (KE + PE) of that object is changed. If the work is
positive work, then the object will gain energy. If the work is
negative work, then the object will lose energy. The gain or loss in
energy can be in the form of potential energy, kinetic energy, or
both. Under such circumstances, the work which is done will be
equal to the change in mechanical energy of the object. Because
external forces are capable of changing the total mechanical energy
of an object, they are sometimes referred to as non-conservative
forces.
When the only type of force doing net work upon an object is an
internal force (for example, gravitational and spring forces), the total
mechanical energy (KE + PE) of that object remains constant. In such
cases, the object's energy changes form. For example, as an object
is "forced" from a high elevation to a lower elevation by gravity,
some of the potential energy of that object is transformed into
kinetic energy. Yet, the sum of the kinetic and potential energies
remain constant. This is referred to as energy conservation and will
be discussed in detail later in this lesson.
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When the only forces doing work are internal forces, energy changes
forms - from kinetic to potential (or vice versa); yet the total amount
of mechanical is conserved. Because internal forces are capable of
changing the form of energy without changing the total amount of
mechanical energy, they are sometimes referred to as conservative
forces.
The work-energy theorem describes the relationship between work
and energy. The work-energy theorem states that whenever work is
done, energy changes. We abbreviate “change in” with the delta
symbol, Δ, and say
 Work = ΔKE
The study of the various forms of energy and the transformations
from one form to another is the law of conservation of energy. The
law of conservation of energy states that energy cannot be created
or destroyed. It can be transformed from one form into another, but
the total amount of energy never changes.
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There are six types of simple machine:
A machine is a tool used to make work easier. Simple machines are
simple tools used to make work easier. Compound machines have
two or more simple machines working together to make work easier.
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Inclined Plane: A plane is a flat surface. For example, a smooth
board is a plane. Now, if the plane is lying flat on the ground, it isn't
likely to help you do work. However, when that plane is inclined, or
slanted, it can help you move objects across distances. And, that's
work! A common inclined plane is a ramp. Lifting a heavy box onto a
loading dock is much easier if you slide the box up a ramp--a
simple machine.
Wedge: Instead of using the smooth side of the inclined plane, you
can also use the pointed edges to do other kinds of work. For
example, you can use the edge to push things apart. Then, the
inclined plane is a wedge. So, a wedge is actually a kind of inclined
plane. An axeblade is a wedge. Think of the edge of the blade. It's
the edge of a smooth slanted surface. That's a wedge!
Screw: Now, take an inclined plane and wrap it around a cylinder.
Its sharp edge becomes another simple tool: the screw. Put a metal
screw beside a ramp and it's kind of hard to see the similarities, but
the screw is actually just another kind of inclined plane. How does
the screw help you do work? Every turn of a metal screw helps you
move a piece of metal through a wooden space. And, that's how we
build things!
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Lever: Try pulling a really stubborn weed out of the ground. You
know, a deep, persistent weed that seems to have taken over your
flowerbed. Using just your bare hands, it might be difficult or even
painful. With a tool, like a hand shovel, however, you should win the
battle. Any tool that pries something loose is a lever. A lever is an
arm that "pivots" (or turns) against a "fulcrum" (or point). Think of
the claw end of a hammer that you use to pry nails loose. It's a lever.
It's a curved arm that rests against a point on a surface. As you
rotate the curved arm, it pries the nail loose from the surface. And
that's hard work!
Wheel and Axle: The rotation of the lever against a point pries
objects loose. That rotation motion can also do other kinds of work.
Another kind of lever, the wheel and axle, moves objects across
distances. The wheel, the round end, turns the axle, the cylindrical
post, causing movement. On a wagon, for example, the bucket rests
on top of the axle. As the wheel rotates the axle, the wagon moves.
Now, place your pet dog in the bucket, and you can easily move him
around the yard. On a truck, for example, the cargo hold rests on
top of several axles. As the wheels rotate the axles, the truck moves.
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Pulley: Instead of an axle, the wheel could also rotate a rope or
cord. This variation of the wheel and axle is the pulley. In a pulley, a
cord wraps around a wheel. As the wheel rotates, the cord moves in
either direction. Now, attach a hook to the cord, and you can use the
wheel's rotation to raise and lower objects. On a flagpole, for
example, a rope is attached to a pulley. On the rope, there are
usually two hooks. The cord rotates around the pulley and lowers
the hooks where you can attach the flag. Then, rotate the cord and
the flag raises high on the pole.
A machine transforms energy from one place to another or
transforms it from one form into another.
In this section we study two specific simple machines, the lever and
the pulley. Below are the three types of lever. We will focus on the
first class lever.
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First Class Lever: If we push down on effort arm, the load is lifted
up. We do work on the effort arm, and the load arm does work on
the load.
If the heat from friction is small enough to neglect, the work input
will be equal to the work output.
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Work input = Work output
Since work equals force times distance, we can say
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(Force x distance)
input
= (Force x distance)
output
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Moving the fulcrum, allows us to input a small force through a large
distance, and lift a large load through a small distance. However, no
machine can multiply work or energy!
The ratio of output force to input force for a machine is called
mechanical advantage. The MA (mechanical advantage) can be
found by taking the ratio of the output force to the input force. On
page 155 of our book, the girl pushes down with a force of 10N
through a distance of 1m. The rock, which weighs 80 N is lifted a
distance of (1/8)m. The MA (mechanical advantage) is (80N)/(10N),
or 8. We can also determine the MA by the ratio of the input
distance to output distance.
Pulley: A major purpose of a pulley is to change the direction of the
input force. You can pull down one a pulley rope, and the rope will
lift the object upward.
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Pulley’s can be used several ways.
A single pulley changes the direction of the lifting force.
For example, if you are lifting a heavy object with a single pulley
anchored to the ceiling, you can pull down on the rope to lift the
object instead of pushing up. The same amount of effort is needed
as without a pulley, but it feels easier because you are pulling down.
A fixed pulley is the only pulley that when used individually, uses
more effort than the load to lift the load from the ground.
The fixed pulley when attached to an unmovable object e.g. a ceiling
or wall, acts as a first class lever with the fulcrum being located at
the axis but with a minor change, the bar becomes a rope.
The advantage of the fixed pulley is that you do not
have to pull or push the pulley up and down.
The disadvantage is that you have to apply more
effort than the load you lift (friction).
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A movable pulley is a pulley that moves with the load.
The movable pulley allows the effort to be less
than the weight of the load. The movable
pulley also acts as a second class lever.
The load is between the fulcrum and
the effort.
The main advantage of a movable pulley is that you
use less effort to pull the load.
The main disadvantage of a movable pulley is that
you have to pull or push the pulley up or down.
If you add a second pulley, the amount of effort
to lift the heavy object seems much less .
For example, to lift a box weighing 150 N, one
would need to exert 150 N of force without the
help of pulleys.
However, by using just two pulleys, the person
would only need to use 75 N of force.
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A combined pulley makes life easier as the effort
needed to lift the load is less than half the
weight of the load.
The main advantage of this pulley is that the
amount of effort is less than half of the load.
The main disadvantage is it travels a very long
distance.
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A major factor in the usefulness of a machine is its efficiency.
A machine converts the force provided from an input energy into
motion that changes the magnitude or direction of that force. This
motion against a resistive force is the work done by the machine.
According to the Law of Conservation of Energy, the total input
energy must equal the total output energy. However, some of the
output energy does not contribute to the output work and is lost to
such things as friction and heat.
The efficiency of a machine is the ratio of the input energy to the
useful output work.
Questions you may have include:
 What is the work done by a machine?
 What role does the Conservation of Energy play in machines?
 What is the efficiency of a machine?
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The efficiency of a machine is the output work or energy divided by
the input work or energy.
 Efficiency = Wo/Wi
As an illustration of the losses in all machines, a simple lever loses
about 2% of the input energy to internal friction at its fulcrum, such
that its efficiency is 98%. If 100 joules of work is input, 98 joules of
work is the output.
On the other hand, the efficiency of an automobile is only around
15%. About 75% of the energy is lost through wasted heat from the
engine and another 10% is lost due to internal friction, including
losses from tire friction.
The usefulness of a machine is determined by its efficiency. A
machine converts the force provided from an input energy into
output work. The Law of Conservation of Energy requires that the
total input energy must equal the total output energy. Some output
energy does not contribute to the output work and is lost to friction
or heat. The efficiency of a machine is the ratio of the input energy
to the useful output work (output divided by input).
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In any machine, some energy is transformed into atomic or
molecular kinetic energy --- making the machine warmer. We say
this wasted energy is dissipated as heat.
The efficiency of a machine is the ratio of useful energy output to
total energy input, or the percentage of work input that is converted
to work output.
useful work output
 Efficiency =
total work input
Efficiency can also be expressed as the ratio of actual mechanical
advantage to theoretical mechanical advantage.
actual mechanical advantage
Efficiency =
theoretical mechanical advantage
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MECHANICAL ADVANTAGE OF THE INCLINED PLANE
Complex Machines:
A car jack is a simple example of a complex
machine that increases the applied force.
The upward force exerted by the jack is greater
than the downward force you exert on the
handle.
However, the distance you push the handle down
is greater than the distance the car is pushed
upward.
Because work is the product of force and
distance, the work done by the jack is equal to
the work you do on the jack.
The jack increases the applied force, but it
doesn’t increase the work done.
As physicists learned in the nineteenth century, transforming 100%
of thermal energy into mechanical energy IS NOT POSSIBLE. Some
heat must flow from the engine. Friction adds more to the energy
loss. Even the best designed gasoline-powered automobile engines
are unlikely to be more than 35% efficient!
On top of these contributors to inefficiency, the fuel does not burn
completely. A certain amount of it goes unused. We can look at
inefficiency in this way: In any transformation there is a dilution of
the amount of useful energy. Useful energy ultimately becomes
thermal energy, Energy is not destroyed, it is simply degraded.
Through heat transfer, thermal energy is the graveyard of useful
energy.
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Every living cell in every organism is a machine. Like any machine, living
cells need an energy supply. Most living organisms on this planet feed on
various hydrocarbon compounds that release energy when they react with
oxygen. There is more energy stored in gasoline than in the products of its
combustion. ~ There is more energy stored in the molecules in food
than there is in the reaction products after the food is metabolized.
This energy difference sustains life.
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The Sun is the source of practically all our energy on Earth!
Solar Power : The sun is the single most significant source of energy
to the planet Earth, and any energy that it provides which isn't used
to help plants grow or to heat the Earth is basically lost. Solar power
can be used with solarvoltaic power cells to generate electricity.
Certain regions of the world receive more direct sunlight than
others, so solar energy is not uniformly practical for all areas.
Hydropower: The use of hydropower involves using the kinetic
motion in water as it flows downstream, part of the normal water
cycle of the Earth, to generate other forms of energy, most notably
electricity. Dams use this property as a means of generating
electricity. This form of hydropower is called hydroelectricity. Water
wheels were an ancient technology which also made use of this
concept to generate kinetic energy to run equipment, such as a
grain mill.
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Wind: Modern windmills can transfer the kinetic energy of the air
flowing through them into other forms of energy, such as electricity.
There are some environmental concerns with using wind energy,
because the windmills often injure birds who may be passing
through the region.
Nuclear: Certain elements are able to undergo powerful nuclear
reactions, releasing energy which can be harnessed and transformed
into electricity. Nuclear power is controversial because the material
used can be dangerous and resultant waste products are toxic.
Accidents that take place at nuclear power plants, such as
Chernobyl, are devastating to local populations and environments.
Still, many nations have adopted nuclear power as a significant
energy alternative.
Biomass: Biomass is not really a separate type of energy, so much as
a specific type of fuel. It is generated from organic waste products,
such as cornhusks, sewage, and grass clippings. This material
contains residual energy, which can be released by burning it in
biomass power plants. Since these waste products always exist, it is
considered a renewable resource.
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Geothermal: The Earth generates a lot of heat while going about its
normal business, in the form of subterranean steam and magma
among others. The energy generated within the Earth's crust can be
harnessed and transformed into other forms of energy, such as
electricity.
Fuel Cells: Fuel cells are an important enabling technology for the
hydrogen economy and have the potential to revolutionize the way
we power our nation, offering cleaner, more-efficient alternatives to
the combustion of gasoline and other fossil fuels. Fuel cells have the
potential to replace the internal-combustion engine in vehicles and
provide power in stationary and portable power applications because
they are energy-efficient, clean, and fuel-flexible. Hydrogen or any
hydrogen-rich fuel can be used by this emerging technology.
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THE END!!!!!
AT LAST!!!!!!!!!!