It is easy to confuse the concepts of force, energy, and power,
especially since they are synonyms in ordinary speech. The table on
the following page may help to clear this up:
| force | energy | power |
conceptual definition | A force is an interaction
between two objects that causes a push or a pull. A force can be defined as
anything that is capable of changing an object's state of motion. |
Heating an object, making it move faster, or increasing its distance from
another object that is attracting it are all examples of things that would
require fuel or physical effort. All these things can be quantified using a single
scale of measurement, and we describe them all as forms of energy. |
Power is the rate at which energy is transformed from one form to another or transferred
from one object to another. |
operational
definition | A spring scale can be used
to measure force. | If we define a unit of energy
as the amount required
to heat a certain
amount of water by a
1 °C, then we can measure
any other quantity
of energy by transferring
it into heat in water and
measuring the temperature
increase. | Measure the change in the
amount of some form of
energy possessed by an
object, and divide by the
amount of time required
for the change to occur. |
scalar or
vector? | vector - has a direction
in space which is the direction
in which it pulls or
pushes | scalar - has no direction
in space | scalar - has no direction
in space |
unit | newtons (N) | joules (J) | watts (W) = joules/s |
Can it run
out? Does it
cost money? | No. I don't have to
pay a monthly bill for
the meganewtons of force
required to hold up my
house. | Yes. We pay money for
gasoline, electrical energy,
batteries, etc., because
they contain energy. | More power means you
are paying money at a
higher rate. A 100-W
lightbulb costs a certain
number of cents per hour. |
Can it be a
property of
an object? | No. A force is a relationship
between two
interacting objects.
A home-run baseball
doesn't have force. | Yes. What a home-run
baseball has is kinetic energy,
not force. | Not really. A 100-W
lightbulb doesn't have
100 W. 100 J/s is the rate
at which it converts electrical
energy into light. |