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Sci 10 4.2 early theories of heat

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Sci 10 4.2 early theories of heat

  1. 1. 4.2 SCIENTIFIC THEORIES OF HEAT4.2 SCIENTIFIC THEORIES OF HEAT SCIENCE 10 Power pointSCIENCE 10 Power point
  2. 2. 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 warm.warm. They did not understandThey did not understand the science of heat andthe science of heat and energy.energy.
  3. 3. Empedocles – 492-435 BCEmpedocles – 492-435 BC Empedocles’ theoryEmpedocles’ theory consisted of the followingconsisted of the following elements:elements: 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
  4. 4. 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)
  5. 5. The Phlogiston TheoryThe Phlogiston Theory
  6. 6. 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!
  7. 7. 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 exist!exist!
  8. 8. 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 substances.substances. 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.
  9. 9. Joseph BlackJoseph Black Joseph Black defined theJoseph Black defined the caloriecalorie as:as: A unit of heatA unit of heat
  10. 10. 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)
  11. 11. 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?
  12. 12. 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.
  13. 13. Count RumfordCount Rumford Count Rumford madeCount Rumford made the conclusion:the conclusion: HEAT = ENERGYHEAT = ENERGY
  14. 14. Relationship Between Energy andRelationship Between Energy and HeatHeat 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.
  15. 15. 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?
  16. 16. Julius Mayer – An importantJulius Mayer – An important discoverydiscovery 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 Indies.Indies. 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.
  17. 17. 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
  18. 18. 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.
  19. 19. 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??)
  20. 20. 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…
  21. 21. James Prescott JouleJames Prescott Joule Joule was a highly trainedJoule was a highly trained scientist who performed manyscientist who performed many experiments.experiments. 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.
  22. 22. Joule’s ExperimentJoule’s Experiment http://www.einstein-support.co.uk/support/msim/website/experiment/expA_hi-ba
  23. 23. 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_virtu
  24. 24. What isWhat is workwork?? 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)
  25. 25. 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 ??

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