Potential And Kinetic Energy Worksheet Page 4
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29Name:
Date:
7.1 James Prescott Joule
7.1
James Joule was known for the accuracy and precision of his work in a time when exactness of
measurements was not held in high regard. He demonstrated that heat is a form of energy. He studied the
nature of heat and the relationship of heat to mechanical work. Joule has also been credited with finding the
relationship between the flow of electricity through a resistance, such as a wire, and the heat given off from it.
This is now known as Joule’s Law. He is remembered for his work that led to the First Law of Thermodynamics
(Law of Conservation of Energy).
The young student
By 1841, Joule focused
most of his attention on the
James Joule was born near Manchester, England on
concept of heat. He
December 24, 1818. His father was a wealthy brewery
disagreed with most of his
owner. James injured his spine when he was young
peers who believed that
and as a result he spent a great deal of time indoors,
heat was a fluid called
reading and studying. When he became interested in
caloric. Joule argued that
science, his father built him a lab in the basement.
heat was a state of vibration
When James was fifteen years old, his father hired
caused by the collision of
John Dalton, a leading scientist at the time, to tutor
molecules. He showed that
James and his brother, Benjamin. Dalton believed that
no matter what kind of
a scientist needed a strong math background. He spent
mechanical work was done,
four years teaching the boys Euclidian mathematics.
a given amount of mechanical work always produced
He also taught them the importance of taking exact
the same amount of heat. Thus, he concluded, heat
measurements, a skill that strongly influenced James
was a form of energy. He established this kinetic
in his scientific endeavors.
theory nearly 100 years before others truly accepted
that molecules and atoms existed.
Brewer first, scientist second
On his honeymoon
After their father became ill, James and Benjamin ran
the family brewery. James loved the brewery, but he
In 1847, Joule married Amelia Grimes, and the couple
also loved science. He continued to perform
spent their honeymoon in the Alps. Joule had always
experiments as a serious hobby. In his lab, he tried to
been fascinated by waterfalls. He had observed that
make a better electric motor using electromagnets.
water was warmer at the bottom of a waterfall than at
James wanted to replace the old steam engines in the
the top. He believed that the energy of the falling
brewery with these new motors.
water was transformed into heat energy. While he and
his new bride were in the Alps, he tried to prove his
Though he learned a lot about magnets, heat, motion,
theory. His experiment failed because there was too
and work, he was not able to change the steam engines
much spray from the waterfall, and the water did not
in the brewery. The cost of the zinc needed to make
fall the correct distance for his calculations to work.
the batteries for the electric motors was much too
high. Steam engines fired by coal were more cost
From 1847–1854, Joule worked with a scientist named
efficient.
William Thomson. Together they studied
thermodynamics and the expansion of gases. They
The young scientist
learned how gases react under different conditions.
Their law, named the Joule-Thomson effect, explains
In 1840, when he was only twenty-two years old,
that compressed gases cool when they are allowed to
Joule wrote what would later be known as Joule’s
expand under the right conditions. Their work later led
Law. This law explained that electricity produces heat
to the invention of refrigeration.
when it travels through a wire due to the resistance of
the wire. Joule’s Law is still used today to calculate
James Joule died on October 11, 1889. The international
the amount of heat produced from electricity.
unit of energy is called the Joule in his honor.
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