is the transfer of energy."
is done on an object when you transfer energy to that object.
For introductory thinking, this is the best definition of
you put energy into an object, then you do work on that
a first object is the agent that gives energy to a second
object, then the first object does work on the second object.
The energy goes from the first object into the second object.
At first we will say that if an object is standing still,
and you get it moving, then you have put energy into that
example, a golfer uses a club and gets a stationary golf
ball moving when he or she hits the ball. The club does
work on the golf ball as it strikes the ball. Energy leaves
the club and enters the ball. This is a transfer of energy.
Thus, we say that the club did work on the ball.
before the ball was struck, the golfer did work on the club.
The club was initially standing still, and the golfer got
it moving when he or she swung the club.
almost all cases considered when studying mechanical forms
of energy, when work is done on an object a force is applied
to the object, and the object is displaced while this force
is acting upon it. That is, the object moves as a result
of a force being placed on it.
the previous golf example the club places a force on the
ball, and this force acts on the ball over the short distance
through which the club and the ball are in contact as the
ball is being hit. Energy is transferred as the force acts
over this displacement.
amount of work is calculated by multiplying the force times
the displacement. That formula looks like this:
= F * d
first we will consider only forces that are aimed in the
same direction as the displacement. For example, we will
imagine an object being pushed horizontally to the right,
and the object will be moving horizontally to the right
as a result of this applied force.
Conservation of energy
To scientists, conservation of energy is not saving energy.
The law of conservation of energy says that energy is neither
created nor destroyed. When we use energy, it doesn’t disappear.
We change it from one form of energy into another. A car engine
burns gasoline, converting the chemical energy in gasoline
into mechanical energy. Solar cells change radiant energy
into electrical energy. Energy changes form, but the total
amount of energy in the universe stays the same. Scientists
at the Department of Energy think they have discovered a mysterious
new form of energy called "dark energy" that is actually causing
the universe to grow!
is the amount of useful energy you get from a system. A perfect,
energy-efficient machine would change all the energy put in
it into useful work—an impossible dream. Converting one form
of energy into another form always involves a loss of usable
energy. In fact, most energy transformations are not very
efficient. The human body is a good example. Your body is
like a machine, and the fuel for your machine is food. Food
gives you the energy to move, breathe, and think. But your
body isn’t very efficient at converting food into useful work.
Your body is less than five percent efficient most of the
time. The rest of the energy is lost as heat. You can really
feel that heat when you exercise!