Work. Power. Еnergy.
Work is a word with a large number of meanings.
It can be a noun or a verb. There is often a problem when a common English word is used as part of a
strict scientific vocabulary. The difficulty arises because some of the common meanings conflict with the
scientific meaning.
Measuring work
Work is done when a force causes an object to move or to change the way it is moving. But knowing that work
has been done does not tell-how much work has been done. How is work measured?
Whenever work is done, a push or a pull-that is, a force must cause an object to move while the push or the pull
is acting on the object. To measure the amount of work done, you need to know two facts. One is the amount of
force used to make the object move. The other is how far the object moves while the force is acting on it.
When the amount of force used and the distance an object moves while a force acts on it are known, the amount
of work done can be found. The amount of work done is equal to the amount of force used multiplied by the
distance the object moves while the - force acts on it. Here is another way to write this:
Force * Distance = Work
A = F* S
Units for measuring work
Scientists all over the world have been using metric units to measure for a long time.
In many countries all people use metric units for measuring. Most people in the
United States, however, use units called English units. Now people in this country
are being urged to use metric units. In this section metric units for measuring work
will be described and used. English units will also be given, usually in parentheses
The metric unit for' measuring distance is the meter . One meter is a little longer than three feet. The metric unit
for measuring force is the newton. A newton is not a large amount of force. It is a little less than 1/4 pound.
Earlier it was stated that the amount of work is equal to the force times the distance.
The unit of work is Newton * 1 metre. This unit is named the joule (J). 1 joule is the work done
when a force of 1 Newton moves its point of application through a distance of 1 metre.
Power. Unit of power
What does a scientist mean by the word «power"?
How is power measured?
'Why did James Watt describe machines in terms of horsepower?
What is power?
Suppose you used a force of 150 newtons to move a box of books 10 meters. You would have done 1500
newton-meters of work. You would have done the same amount of work whether you took ten seconds or thirty.
seconds to move the box. But, the faster you worked, the sooner the work would have been done.
The amount of work done in a given period of time, say one second, is the rate of work. Scientists use the word
«power" when they speak of the rate of work.
In the example, you would have done 1 500 newtonmeters of work in moving. the box of books. However, the
rate of work would have been three times faster if you did the work in ten seconds instead of in thirty. That is, it
would have taken more power to move the box in less time.
Think about this example: A bulldozer digs up and moves a lot of dirt in a short time. A bulldozer has a lot of
power. A person could dig up and move as much dirt as a bulldozer. But a person does not have as much power
as a bulldozer. So a person would have to work for a long time to do as much work as a bulldozer does in a short
time.
Measuring power
Power is measured by dividing the amount of work .done by the time it takes to do the work. This can be shown
as follows:
N = A/t
Units
The dimension of power is energy divided by time. The SI unit of power is the watt (N), which is equal to
one joule per second.
The watt ( symbol: W) is a derived unit of power in the International System of Units (SI), named after the
Scottish engineer James Watt (1736–1819). The unit measures the rate of energy conversion. It is defined as
one joule per second.
What does a scientist mean by the tenn "energy'?
lVhat are some kinds of energy?
'Vhat are two ways in which ob;ects can gain potential energy?
What is energy?
Energy is closely related to work. In fact, the term "work" is
often used to explain what scientists mean by the term "energy."
Energy is described as the ability to do work. If something has
energy, it is able to do work.
To scientists, there is only one meaning for the term "work."
That is, work is done only when a force causes a change in the
way something is moving. However, there is more than one
kind of energy. Scientists often divide energy into two groups:
potential energy and kinetic energy.
Potential energy. Kinetic energy. ( Е).
In physics, potential energy is the energy stored in a body or in a system due to its position in a force field or due
to its configuration.
In the International System of Units (SI), energy is measured in joules, but in some fields other units such as
kilowatt-hours and kilocalories are also used.
Any form of energy can be transformed into another form.
Energy may not be created nor destroyed. This principle, the conservation of energy, was first
postulated in the early 19th century.
The kinetic energy of an object is the energy which it possesses due to its motion.