Calories (Units of Energy)
Year of Discovery: 1843
What Is It? All forms of energy and mechanical work are equivalent and can
be converted from one form to another.
Who Discovered It? James Joule
Why Is This One of the 100 Greatest?
We now know that mechanical work, electricity, momentum, heat, magnetic force,
etc., can be converted from one to another. There is always a loss in the process, but it can be
done. That knowledge has been a tremendous help for the development of our industries
and technologies. Only 200 years ago, the thought had not occurred to anyone.
James Joule discovered that every form of energy could be converted into an equivalent amount of heat. In so doing, he was the first scientist to come to grips with the general
concept of energy and of how different forms of energy are equivalent to each other. Joule’s
discovery was an essential foundation for the discovery (40 years later) of the law of conservation of energy and for the development of the field of thermodynamics.
How Was It Discovered?
Born on Christmas eve, 1818, James Joule grew up in a wealthy brewing family in
Lancashire, England. He studied science with private tutors and, at the age of 20, started to
work in the family brewery.
Joule’s first self-appointed job was to see if he could convert the brewery from steam
power to new, “modern” electric power. He studied engines and energy supplies. He studied electrical energy circuits and was fascinated to find that the electrical wires grew hot
when current ran through them. He realized that some of the electrical energy was being
converted into heat.
He felt it was important for him to quantify that electrical energy loss and began experiments on how energy was converted from electricity to heat. Often he experimented with
little regard for safety—his or others. More than once, a servant girl collapsed unconscious
from electrical shocks during these experiments. While he never converted the brewery to
electrical power, these experiments turned his focus to the process of converting energy
from one form to another.
Joule was deeply religious, and it seemed right to him that there should be a unity for
all the forces of nature. He suspected that heat was somehow the ultimate and natural form
for calculating the equivalence of different forms of energy.
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