4.2 SCIENTIFIC THEORIES OF HEAT4.2 SCIENTIFIC THEORIES OF HEAT
SCIENCE 10 Power pointSCIENCE 10 Power point
Early Theories of HeatEarly Theories of Heat
1-2 million years ago the1-2 million years ago the
first hominid (human-first hominid (human-
like) species was calledlike) species was called
Homo erectus.Homo erectus.
They lived in Africa andThey lived in Africa and
were thought to be thewere thought to be the
first humans to use fire tofirst humans to use fire to
cook their food and keepcook their food and keep
They did not understandThey did not understand
the science of heat andthe science of heat and
Empedocles – 492-435 BCEmpedocles – 492-435 BC
Empedocles’ theoryEmpedocles’ theory
consisted of the followingconsisted of the following
All matter was made fromAll matter was made from
a combination of thea combination of the 44
elements: EARTH, AIR,elements: EARTH, AIR,
FIRE and WATERFIRE and WATER
He thought that whenHe thought that when
objects burned, the fireobjects burned, the fire
within them was releasedwithin them was released
The Phlogiston TheoryThe Phlogiston Theory
early 1700searly 1700s
Scientists believed that substances that couldScientists believed that substances that could
burn contained an invisible fluid calledburn contained an invisible fluid called
They believed that phlogiston flowed out of anThey believed that phlogiston flowed out of an
object when the object burned.object when the object burned.
When wood burned, the phlogiston flowed out,When wood burned, the phlogiston flowed out,
leaving only ashes (therefore ashes had lessleaving only ashes (therefore ashes had less
mass than original wood)mass than original wood)
An example that wouldAn example that would
dispute this theory:dispute this theory:
2 Mg (s) + O2 Mg (s) + O22 (g)(g) 2 MgO (s)2 MgO (s)
When Mg burned the ashesWhen Mg burned the ashes
weighed MORE!weighed MORE!
So maybe phlogiston didn’tSo maybe phlogiston didn’t
always leave when substancesalways leave when substances
were burnedwere burned
Or maybe….phlogiston didn’tOr maybe….phlogiston didn’t
The Caloric TheoryThe Caloric Theory
In the late 1700s, it was believed that “caloric” orIn the late 1700s, it was believed that “caloric” or
“heat” was a massless fluid that was found in all“heat” was a massless fluid that was found in all
This theory was called theThis theory was called the
Scientists believed that this “caloric” couldn’t beScientists believed that this “caloric” couldn’t be
created or destroyed, but could flow from onecreated or destroyed, but could flow from one
substance to another. In fact, many scientists believedsubstance to another. In fact, many scientists believed
it flowed from warm objects to cooler ones.it flowed from warm objects to cooler ones.
Joseph BlackJoseph Black
Joseph Black defined theJoseph Black defined the
A unit of heatA unit of heat
The Caloric TheoryThe Caloric Theory
Can you see any problems/limitations withCan you see any problems/limitations with
the “Caloric Theory”?the “Caloric Theory”?
Caloric Theory = Caloric is a massless fluidCaloric Theory = Caloric is a massless fluid
that flows from one object (warmer) tothat flows from one object (warmer) to
another (cooler)another (cooler)
Benjamin Thompson (aka Count Rumford)Benjamin Thompson (aka Count Rumford)
Count Rumford lived in Bavaria,
Germany and was in charge of
looking after the military
He noticed that after boring a
hole into the metal cannon, the
tools and metal became very hot
– but weren’t hot previously.
How would the Caloric Theory
Count RumfordCount Rumford
The count discovered
that the “caloric” or
“heat” as he called it,
was not transferred from
inside a hotter object to a
colder one – instead the
“heat” was a type of
energy that was
transferred from the
mechanical energy due
Count RumfordCount Rumford
Count Rumford madeCount Rumford made
the conclusion:the conclusion:
HEAT = ENERGYHEAT = ENERGY
Relationship Between Energy andRelationship Between Energy and
Scientists now knew that heat and energyScientists now knew that heat and energy
were related – but wanted to find awere related – but wanted to find a
mechanical equivalent of heat – in othermechanical equivalent of heat – in other
words, they wanted to quantify or measurewords, they wanted to quantify or measure
heat in some way.heat in some way.
Scientists competed to be the first to comeScientists competed to be the first to come
up with a measurable quantity for heat –up with a measurable quantity for heat –
which was finally discovered in the 1800s.which was finally discovered in the 1800s.
Julius Mayer – 1800sJulius Mayer – 1800s
Julius Mayer actually was the scientist whoJulius Mayer actually was the scientist who
found real evidence of a relationshipfound real evidence of a relationship
between energy and heat.between energy and heat.
How did he do this?How did he do this?
Julius Mayer – An importantJulius Mayer – An important
Julius Mayer served as a ship’sJulius Mayer served as a ship’s
doctor on a voyage to the Eastdoctor on a voyage to the East
Many sailors would get sick –Many sailors would get sick –
and “blood-letting” was aand “blood-letting” was a
common practice to rid thecommon practice to rid the
sailor of “toxins”. The doctorsailor of “toxins”. The doctor
would puncture the sailor’swould puncture the sailor’s
vein and allow some blood tovein and allow some blood to
escape – believing it wouldescape – believing it would
cure the sailor.cure the sailor.
Mayer’s findings:Mayer’s findings:
After performing many blood-letting “operations”,After performing many blood-letting “operations”,
Mayer noticed that the blood of the sailors (whoMayer noticed that the blood of the sailors (who
lived predominantly in Northern climates) waslived predominantly in Northern climates) was
darker reddarker red than the blood of the natives (who livedthan the blood of the natives (who lived
in tropical climates)in tropical climates)
Mayer knew thatMayer knew that
darker blood meantdarker blood meant
less oxygen whereasless oxygen whereas
lighter blood meantlighter blood meant
more oxygen.more oxygen.
Native’s blood Sailors’ blood
Mayer’s findings con’tMayer’s findings con’t
Mayer concluded that lighter blood meantMayer concluded that lighter blood meant
more Omore O22 and therefore less work done by theand therefore less work done by the
body (Mayer knew that work done by thebody (Mayer knew that work done by the
body = less oxygen in blood = darker blood)body = less oxygen in blood = darker blood)
Mayer determined that the Northern sailor’sMayer determined that the Northern sailor’s
used quite a bit of body energy to stay warmused quite a bit of body energy to stay warm
– therefore there was less oxygen in the– therefore there was less oxygen in the
blood which meant darker blood overall.blood which meant darker blood overall.
Mayer’s Downfall…Mayer’s Downfall…
Finally! Someone could quantify heat – possiblyFinally! Someone could quantify heat – possibly
even measure it! If Julius Mayer could figure outeven measure it! If Julius Mayer could figure out
how to calculate how much energy the bodyhow to calculate how much energy the body
expended when staying warm – he could put aexpended when staying warm – he could put a
quantity or unit on heat.quantity or unit on heat.
Sounds good! Why didn’t he publish this and getSounds good! Why didn’t he publish this and get
really famous? (Obviously he didn’t – have you everreally famous? (Obviously he didn’t – have you ever
even heard of Julius Mayer??)even heard of Julius Mayer??)
Julius Mayer tried to write a
scientific paper outlining his
theories on heat and energy
but it was overlooked by the
scientific community because
he lacked the formal
education necessary to write
a good paper.
By the time he had gone back
to school to learn how to
write a paper… another
scientist had quickly
published all of these ideas!
He became QUITE famous…
James Prescott JouleJames Prescott Joule
Joule was a highly trainedJoule was a highly trained
scientist who performed manyscientist who performed many
He came up with a mechanical equivalent ofHe came up with a mechanical equivalent of
heat – called a JOULE (J).heat – called a JOULE (J).
The Joule is now used to measure energy.The Joule is now used to measure energy.
Joule's apparatus for measuring the mechanical equivalent of
heat. A descending weight attached to a string causes a
paddle immersed in water to rotate and the "work" of the
falling weight is converted into "heat" by agitating the water
and raising its temperature.
What isWhat is workwork??
W = FΔdW = FΔd
W = work (J) (Joules)W = work (J) (Joules)
F = force (N) (Newtons) (F = mg)F = force (N) (Newtons) (F = mg)
Δd = change in distance (m) (metres)Δd = change in distance (m) (metres)
Work ProblemsWork Problems
F = 1.0 NF = 1.0 N
Δd = 0.35 mΔd = 0.35 m
W = ?W = ?
W = FΔdW = FΔd
Answer is ??Answer is ??