Mechanical Heat

Program 21

Lesson 3.6

1.  Question
2.  Objectives
3.  Introduction
4.  Caloric theory
5.  Joseph Black
6.  Heat as Energy
7.  Count Rumford
8.  Mechanical Equivalent of Heat
9.  James Prescott Joule
10.  Conservation of Energy
11.  Summary

Text References

Spielberg & Anderson 124-127; 130-138

Booth & Bloom 183-186

Coming Up

In this lesson we will study the development of the concept of heat as a form of energy. We will learn of Black's early studies of heat, and his concept of heat as a fluid. Then we will learn how Count Rumford, one of the more colorful characters we will encounter, connected heat with work and primed the pump for Joule to complete the concept of conservation of energy by establishing a quantitative link between heat and energy. At last we see that our suspicions about heat, that it is a form of energy, were proven beyond a doubt.

 1.  Questions

  1.  Briefly describe two competing theories of heat which drove inquiry

  2.  Describe the relationship between temperature and heat

  3.  What did Joseph Black contribute to the study of heat?

  4.  What is calorimetry and how does it measure heat?

  5.  Discuss the statement:  Calorimetry depends on the fact that heat is conserved.

  6.  What was caloric theory and what were the properties of caloric?

  7.  What characteristics do heat and energy have in common?

  8.  What is the meaning and significance of the term "mechanical equivalent of heat"?

  9.  Compare the contributions of Rumford and Joule to the development of the concept of heat as a form of energy?

  10.  How does the modern concept of conservation of energy differ from earlier ones?

  11.  Describe the three types of heat transfer and give an example of the conditions in which each is effective.

 2.  Objectives

  1.  Describe the age old quandary concerning the nature of heat

  2.  Describe the properties of the caloric fluid

  3.  Detail the contributions of Joseph Black and Count Rumford to our understanding of heat

  4.  Define the mechanical equivalent of heat and discuss its significance.

  5.  Describe the experiments of James Joule which led to the modern concept of conservation of energy

  6.  Describe the types of energy known today and the types of transformations among them


3.  Introduction

  3.1.  Much controversy revolved around the applicability of the Newtonian paradigm outside of mechanics

   3.1.1.  could chemistry be explained by mechanical forces?
   3.1.2.  what is the nature of the forces?
   3.1.3.  how can the forces be measured in the laboratory?
   3.1.4.  can heat and temperature be incorporated into the paradigm, and if so, how?

  3.2.  Nature of heat was debated by early Greek philosophers

   3.2.1.  is heat a substance or invisible, chaotic motion of ultimate particles of ordinary matter ?
   3.2.2.  Greeks talked themselves out of the existence of atoms so rejected kinetic theory

  3.3.  Competing theories divided scientists until mid- nineteenth century

   3.3.1.  mechanical phenomenon (kinetic theory) or imponderable  fluid (caloric theory)  vibration of “corpuscles” of matter vs. substance with unusual properties  could neither be weighed nor measured
   3.3.2.  Newton, Boyle, Hooke, Huygens favored mechanical theory
   3.3.3.  chemists wanted to know how to measure the forces and vibrations, and what principles were involved

  3.4.  1738 - French Academy sponsored a prize essay contest on the nature of heat

   3.4.1.  all three winners favored the caloric concept of heat as a substance
   3.4.2.  view was developed mathematically and proved useful in description of many thermal phenomena
   3.4.3.  Black’s calorimetric scheme fitted the caloric hypothesis and gave it added prestige
   3.4.4.  kinetic interpretation remained an open alternative, but caloric theory was more fully developed and more popular

  3.5.  Two competing theories

   3.5.1.  Kinetic Theory and Caloric Theory

  3.6.  Kinetic theory

   3.6.1.  revived atomic theory in nineteenth century led to modern interpretations of kinetic theory
   3.6.2.  resolved controversy of imponderable vs. mechanical nature
   3.6.3.  combined Newtonian mechanical paradigm and atomic theory
   3.6.4.  joined atomic and Newtonian paradigms into a larger, stronger body of knowledge
   3.6.5.  required for full understanding of the nature of heat  not necessary for understanding of principles involved in everyday matters  not necessary to deal quantitatively with heat as a form of energy and transformation of mechanical energy into thermal energy
   3.6.6.  we will study details of kinetic theory later
   3.6.7.  next:  Caloric Theory

4.  Caloric theory

  4.1.  The fluid theory of heat

  4.2.  An incorrect theory which serves as a model for scientific growth

   4.2.1.  language retains vestiges of concept
   4.2.2.  heat flows, objects soak up heat
   4.2.3.  leads to confusion:  we speak of it as a substance while told that it is not  metaphor
   4.2.4.  Lavoisier coined the term later in 1787  firmly entrenched by 1780  largely discredited by 1850

  4.3.  conservation of heat was a basic premise

   4.3.1.  heat lost by one object is gained by another
   4.3.2.  this is true and still a basis for calorimetry

  4.4.  heat was thought of as a substance

   4.4.1.  fluid = can flow
   4.4.2.  a “fluid” called caloric

  4.5.  Properties of Caloric

   4.5.1.  massless
   4.5.2.  could not be created nor destroyed
   4.5.3.  all substances contain caloric and absorb or release it
   4.5.4.  flows from hot to cold objects or substances
   4.5.5.  counterbalanced attractive forces of "particles of matter"  self repulsion caused it to flow from higher to lower concentration  kind of like pressure in a balloon

  4.6.  state of matter determined by amount of caloric

   4.6.1.  caloric surrounds the particles of matter causing them to swell
   4.6.2.  caloric occupied space, so gas has lots of caloric

5.  Joseph Black (1728-1799)

  Black, Joseph (1728-99), was a Scottish physician who was also a chemist and physicist. He became professor of medicine at Glasgow and later of chemistry at Edinburgh. He performed early quantitative experiments and was among the first to emphasize the importance of such experiments to chemists. He discovered that carbon dioxide is produced by respiration, burning of charcoal, and fermentation; that it behaves as an acid; and that it is probably found in the atmosphere. He founded the theory of latent heat and investigated the concept of specific heat but was unable to fit them into place because of his belief in the phlogiston theory.  These theories of specific heat and latent heat furnished a basis for Lavoisier's caloric theory of heat.  He also invented a form of ice calorimeter.

  5.1.  performed  quantitative experiments in chemistry and emphasized their importance

   5.1.1.  studied carbon dioxide

  5.2.  founded theory of latent and specific heat

   5.2.1.  unable to fit theories into place because of his belief in pholgiston and caloric

  5.3.  worked out first satisfactory method for measuring heat

   5.3.1.  invented calorimeter
   5.3.2.  ice calorimeter was first type
   5.3.3.  insulated water calorimeter later

  5.4.  noted that heat is conserved when transferred

  5.5.  Calorimetry

   5.5.1.  Measurement of Heat

    calorimeter  uses calorimeter  assumes conservation of heat  depends on change in temperature of a given amount of a certain substance, usually water  heats units standardized by comparing with change of temperature of water
   5.5.2.  heat gained or lost depends on mass, specific heat of substance and temperature change

    heat defined  delta H = mc delta T
   5.5.3.  heat gained by one substance = heat lost by another substance  conservation of heat  assumes total transfer  assumes no “loss” to surroundings  assumes no outside work done
   5.5.4.  heat of combustion  bomb calorimeter  foods and fuels burned to determine usable energy content  reported in kcal/kg or J/kg
   5.5.5.  heat of reaction  combustion is one type of reaction  solution, acid-base reactions, other chemical reactions

  5.6.  specific heat

   5.6.1.  clarified distinction between heat and temperature
   5.6.2.  defined and measured specific heats of various substances
   5.6.3.  water tank model

    Water Tank Model  heat:temperature :: size of tank: level in tank  heat is transferred, temperature is intensity of heat  level depends on amount transferred and size of reservoir

6.  Heat as Energy

  6.1.  gradually displaced caloric theory of heat

  6.2.  heat shares certain characteristics with energy

   6.2.1.  appears when work is done
   6.2.2.  appears when mechanical energy "disappears"
   6.2.3.  systems move naturally from high to low energy
   6.2.4.  is conserved during interactions

7.  Count Rumford


  Benjamin Thompson a.k.a
  Count Rumford

  7.1.  showed caloric had no gravitational mass

   7.1.1.  no difference in weight between hot and cold objects
   7.1.2.  countered by Aristotlean arguement:  not ordinary matter so not affected by gravity
   7.1.3.  precedent in imponderable quintessential matter (Aristotle)

  7.2.  questioned caloric theory

Rumford's Boring

   7.2.1.   based on friction
   7.2.2.  "by accident" while supervising boring of cannons
   7.2.3.  heat was produced as long as horses were working
   7.2.4.  theory held than caloric was released when metal is reduced to chips  more heat was produced when drill bit was dull and produced fewer chips
   7.2.5.  how can motion of horses create an inexhaustible supply of caloric?

  7.3.  concluded heat was due to motion

   7.3.1.  motion causes heating through friction
   7.3.2.  heating continues so long as motion continues
   7.3.3.  not the first to think so  F. Bacon (1620): "Heat itself . . . is motion and nothing else.”  Boyle and Hooke expressed similar thought  Newton thought “corpuscles” of matter in motion could explain temperature
   7.3.4.  no one able to explain how heat in the form of motion was conserved

  7.4.  produced a rough proportion between quantity of work and quantity of heat

   7.4.1.  experiments were not convincing enough to caloric followers

  7.5.  relationship was qualitatively sound but quantitatively weak

8.  Mechanical Equivalent of Heat

  8.1.  heat is produced as long as mechanical processes continue

   8.1.1.  amount of heat is proportional to amount of mechanical energy dissipated
   8.1.2.  if there is a quantitative proportionality then we might be justified in assuming that mechanical energy and heat are different forms of the same thing
   8.1.3.  Rumford had failed to establish the quantitative relationship convincingly

  8.2.  ratio of work to heat is called the mechanical equivalent of heat

   Mechanical Equivalent
   8.2.1.  J = 4.18 Joule/cal

  8.3.  relationship was finally established by Joule

9.  James Prescott Joule (1818-1899)


Here are two brief online biographies of Joule:

  9.1.  waterfall sparked his interest

   9.1.1.  water should be warmer at bottom than at top due to loss of potential energy
   9.1.2.  attempts to measure temperature differences failed

  9.2.  invented accurate and reliable thermometers

  9.3.  saw potential of  newly invented electric motor

   9.3.1.  Faraday invented motors and generators in 1810s
   9.3.2.  Joule hoped to replace steam power with electric power in family brewery  cost of zinc consumed in batteries was greater than cost of coal

  9.4.  many types of experiments tested relationships in every observable situation

   9.4.1.  heat measured by calorimetry
   9.4.2.  measured heat developed by electric current from chemical reactions in batteries  discovered/invented in 1803
   9.4.3.  measured heat from electric current produced by electrical generator  source of generator current is mechanical work to turn it
   9.4.4.  stated Joule’s law  heating produced by an electric current is proportional to the square of the current
   9.4.5.  friction between moving cast iron plates
   9.4.6.  various liquids heated by rotating paddles

Joule's Churn

   At this London Science Museum site you can view a photograph of Joule's churn.

   9.4.7.  liquid forced through small tubes by mechanical pressure

  9.5.  determined quantitative relationship between work and heat

   9.5.1.  called the mechanical equivalent of heat
   9.5.2.  1 calorie = 4.18 Joules (1 kcal = 4180 J)
   9.5.3.  joules and calories are different units for same quantity
   9.5.4.  input in work (joules) appears as heat (calories)

  9.6.  creditied with general statment and proof of conservation of energy (along with Mayer)

   9.6.1.  established through 40 years of extensive experimentation
   9.6.2.  includes not only mechanical energy
   9.6.3.  added heat, electrical energy and chemical energy to work/energy equation

10.  Conservation of Energy

  10.1.  Energy exists in many forms which are all interconvertible.

   Types of Energy

   10.1.1.  mechanical energy (kinetic and potential)
   10.1.2.  electrical energy
   10.1.3.  elastic energy
   10.1.4.  chemical energy
   10.1.5.  thermal energy
   10.1.6.  radiant energy
   10.1.7.  (nuclear energy)

  10.2.  When energy is transformed none is lost, all can be accounted for.

  10.3.  Energy can neither be created nor destroyed.

  10.4.  Glen Canyon Dam

Glen Canyon Dam

   10.4.1.  solar energy evaporates water and lifts it high in atmosphere  increases potential energy of water  condensation releases latent heat
   10.4.2.  precipitation collects in streams and flows downhill  water has both kinetic and potential energy  some energy is used for erosion and friction
   10.4.3.  stream is dammed to create energy difference due to water level  potential energy is converted to kinetic energy as it falls between levels  kinetic energy of water is transferred to turbine by doing work on it  kinetic energy of turbine is converted to electrical energy by generator
   10.4.4.  electrical energy is transmitted through wires as current and magnetic field
   10.4.5.  final use of energy depends upon the type of transformation at the user end

  10.5.  The amount of energy in a closed system remains constant

  10.6.  Julius Mayer (1814-1878) arrived at same concept independently

   10.6.1.  fascinated by Lavoisier's suggestion that animal heat is generated by regulated combustion  slow combustion of food
   10.6.2.  noticed that venous blood is redder in tropics
   10.6.3.  noticed that animals in tropics did not consume as much oxygen as in colder climates
   10.6.4.  related heat of metabolism to heat loss and work performed by body

  10.7.  Joule and Mayer get recognition after long battle over priority

   10.7.1.  such battles are common in history of science
   10.7.2.  Newton’s calculus vs. Leibnitz’s for example
   10.7.3.  Joule gets the energy unit named after him, Mayer doesn’t

11.  Summary

  In this lesson we have considered a number of the aspects of heat as a form of energy, from the historical and physical perspective.
  The focus is that mechanical energy, although the model for energy and conservation in general is only one of many forms of energy, including heat.
  Loke momentum, energy can be transferred from one object to another.  Unlike momemtum, there are many different forms of energy, and it can be transformed from one type to the other even in the same object.
  The principle of conservation of energy, as stated by Joule and Mayer, suggests that the total amount of energy in the universe remains constant although it may change forms many imes.
  11.1.  Contributions of Black, Rumford, Joule
  11.2.  Caloric theory vs. energy theory of heat
  11.3.  Question remains as to how heat fits into Newtonian paradigm.
  11.4.  There are many different forms of energy
   11.4.1.  mechanical
   11.4.2.  chemical
   11.4.3.  thermal
   11.4.4.  electrical
   11.4.5.  radiant
   11.4.6.  nuclear
  11.5.  Energy can be transformed back and forth between the various types
  11.6.  Much of our modern technology is devoted to energy transformations
  11.7.  When energy is transformed none is lost, all can be accounted for in one form or another
  11.8.  The amount of energy in a closed system remains constant
  11.9.  Energy can neither be created nor destroyed.
  11.10.  Conservation of energy vs. energy conservation

Now we are ready to undertake our studies of the nature of matter and see how that will tie in with our studies of physics., and how the two separate fields of study will merge into one solid and interrelated paradigm.We will do that in the next lesson.