4.2 SCIENTIFIC THEORIES OF HEAT4.2 SCIENTIFIC THEORIES OF HEATSCIENCE 10 Power pointSCIENCE 10 Power point

Early Theories of HeatEarly Theories of Heat

1-2 million years ago the 1-2 million years ago the first hominid (human-first hominid (human-like) species was called like) species was called Homo erectus. Homo erectus.

They lived in Africa and They lived in Africa and were thought to be the were thought to be the first humans to use fire to first humans to use fire to cook their food and keep cook their food and keep warm.warm.

They did not understand They did not understand the science of heat and the science of heat and energy.energy.

Empedocles – 492-435 BCEmpedocles – 492-435 BC

Empedocles’ theory Empedocles’ theory consisted of the following consisted of the following elements:elements:

All matter was made from All matter was made from a combination of the a combination of the 4 4 elements: EARTH, AIR, elements: EARTH, AIR, FIRE and WATERFIRE and WATER

He thought that when He thought that when objects burned, the fire objects burned, the fire within them was releasedwithin them was released

The Phlogiston TheoryThe Phlogiston Theoryearly 1700searly 1700s

Scientists believed that substances that could Scientists believed that substances that could burn contained an invisible fluid calledburn contained an invisible fluid called

..

They believed that phlogiston flowed out of an They 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 less leaving only ashes (therefore ashes had less mass than original wood)mass than original wood)

The Phlogiston TheoryThe Phlogiston Theory

An example that would An 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 ashes When Mg burned the ashes weighed MORE! weighed MORE!

So maybe phlogiston didn’t So maybe phlogiston didn’t always leave when substances always leave when substances were burnedwere burned

Or maybe….phlogiston didn’t Or maybe….phlogiston didn’t exist!exist!

The Caloric TheoryThe Caloric Theory

In the late 1700s, it was believed that “caloric” or In 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 substances. substances.

This theory was called the This theory was called the

Scientists believed that this “caloric” couldn’t be Scientists believed that this “caloric” couldn’t be created or destroyed, but could flow from one created or destroyed, but could flow from one substance to another. In fact, many scientists believed substance 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 the Joseph Black defined the

calorie calorie as:as:

A unit of heatA unit of heat

The Caloric TheoryThe Caloric Theory

Can you see any problems/limitations with Can you see any problems/limitations with the “Caloric Theory”?the “Caloric Theory”?

Caloric Theory = Caloric is a massless fluid Caloric Theory = Caloric is a massless fluid that flows from one object (warmer) to that 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 cannons.

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 explain this?

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 to friction.

Count RumfordCount Rumford

Count Rumford made Count Rumford made the conclusion:the conclusion:

HEAT = ENERGYHEAT = ENERGY

Relationship Between Energy and Relationship Between Energy and HeatHeat

Scientists now knew that heat and energy Scientists now knew that heat and energy were related – but wanted to find a were related – but wanted to find a mechanical equivalent of heat – in other mechanical equivalent of heat – in other words, they wanted to quantify or measure words, they wanted to quantify or measure heat in some way.heat in some way.

Scientists competed to be the first to come Scientists 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 who Julius Mayer actually was the scientist who found real evidence of a relationship found 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 important Julius Mayer – An important discoverydiscovery

Julius Mayer served as a ship’s Julius Mayer served as a ship’s doctor on a voyage to the East doctor on a voyage to the East Indies.Indies.

Many sailors would get sick – Many sailors would get sick – and “blood-letting” was a and “blood-letting” was a common practice to rid the common practice to rid the sailor of “toxins”. The doctor sailor of “toxins”. The doctor would puncture the sailor’s would puncture the sailor’s vein and allow some blood to vein and allow some blood to escape – believing it would escape – 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 (who Mayer noticed that the blood of the sailors (who lived predominantly in Northern climates) was lived predominantly in Northern climates) was darker reddarker red than the blood of the natives (who lived than the blood of the natives (who lived in tropical climates)in tropical climates)

Mayer knew thatMayer knew that darker blood meant darker blood meant less oxygen whereasless oxygen whereas lighter blood meant lighter 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 meant Mayer concluded that lighter blood meant more Omore O22 and therefore less work done by the and therefore less work done by the body (Mayer knew that work done by the body (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’s Mayer determined that the Northern sailor’s used quite a bit of body energy to stay warm used 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 – possibly Finally! Someone could quantify heat – possibly even measure it! If Julius Mayer could figure out even measure it! If Julius Mayer could figure out how to calculate how much energy the body how to calculate how much energy the body expended when staying warm – he could put a expended 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 get Sounds good! Why didn’t he publish this and get really famous? (Obviously he didn’t – have you ever really 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 trained Joule was a highly trained scientist who performed many scientist who performed many experiments.experiments.

He came up with a mechanical equivalent of He 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 ExperimentJoule’s Experiment

http://www.einstein-support.co.uk/support/msim/website/experiment/expA_hi-bandwwidth_version/screen_2.htm

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.

Joule’s Experiment

http://www.einstein-support.co.uk/support/msim/website/experiment/exp_B_virtual_exp_flash_1.htm

What is What is workwork??

Work Work = =

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 ??