Julius Sumner Miller: Lesson 22 - Heat Energy Transfer by Conduction

00:14:19
https://www.youtube.com/watch?v=lZk0tC7mNOU

Résumé

TLDRDans cette présentation, Julia Sumner Miller explore le concept de transfert d'énergie thermique par conduction, illustré à travers diverses expériences. Elle commence par comparer la capacité de conduction thermique de deux matériaux, le cuivre et le fer, montrant que le cuivre transfère la chaleur beaucoup plus rapidement. Ensuite, elle présente des expériences démontrant comment la chaleur se propage différemment selon les matériaux, par exemple, pourquoi un papier entourant une barre métallique ne brûle pas ou comment faire bouillir de l'eau dans un gobelet en papier sans le brûler. D'autres expériences incluent l'usage de thermomètres pour visualiser le transfert de chaleur, et des astuces pratiques comme utiliser des clous pour cuire des pommes de terre rapidement. Julia utilise ces démonstrations pour stimuler la curiosité et encourager l'observation des phénomènes physiques.

A retenir

  • 🧪 La conduction est le transfert de chaleur à travers un matériau solide.
  • 🥇 Le cuivre conduit la chaleur plus efficacement que le fer.
  • 🔥 Un papier entourant un métal chaud ne brûle pas facilement.
  • 💧 Faire bouillir de l'eau dans un gobelet en papier est possible sans le brûler.
  • 📏 Les thermomètres en verre peuvent d'abord lire une baisse de température lorsqu'immergés dans de l'eau chaude.
  • 🔍 L'imagination est cruciale pour comprendre la physique.
  • 🍽️ Utiliser des clous pour accélérer la cuisson des pommes de terre est une délicieuse astuce.
  • ☕ Même dans une tasse en papier, l'eau peut être chauffée sans brûler le contenant.
  • 🔬 Le liquide refroidissant rapidement rend un matériau plus difficile à sentir chaud au toucher.
  • 🚬 Les cendriers en verre peuvent aider à éteindre les cigarettes en conduisant la chaleur loin.

Chronologie

  • 00:00:00 - 00:05:00

    Julia Sumner Miller introduit le sujet du transfert d'énergie thermique par conduction, en mentionnant l'importance de comprendre son origine latine. Elle propose une expérience avec deux tiges, une en cuivre et une en fer, fixées ensemble pour démontrer que le cuivre conduit la chaleur beaucoup plus rapidement que le fer lorsqu'elles sont placées dans de l'huile chaude. Un autre exemple est donné avec une tige en bois et une en métal autour desquelles du papier est enroulé : le papier brûle du côté bois et pas du côté métal, car le métal dissipe la chaleur efficacement.

  • 00:05:00 - 00:14:19

    Julia continue par une expérience utilisant un gobelet en papier rempli d'eau, démontrant que l'eau peut bouillir sans que le gobelet ne brûle là où le papier est mince. Elle explique ensuite qu'un thermomètre immergé dans de l'eau chaude montre d'abord une baisse de température due à l'expansion du bulbe de verre avant que la lecture n'augmente. D'autres exemples incluent l'utilisation de clous en fer pour cuire des pommes de terre plus grosses plus rapidement et le rôle de la conduction thermique dans le choix des matériaux pour les ustensiles de cuisine. La démonstration finale est que le papier ne brûle pas dans le gobelet tant que l'eau n'est pas complètement évaporée.

Carte mentale

Mind Map

Questions fréquemment posées

  • Qu'est-ce que la conduction thermique ?

    La conduction thermique est le transfert d'énergie thermique à travers un matériau sans mouvement de la matière elle-même.

  • Quel matériau conduit la chaleur plus rapidement, le cuivre ou le fer ?

    Le cuivre conduit la chaleur environ dix fois plus rapidement que le fer.

  • Pourquoi le papier ne brûle-t-il pas quand il entoure une barre métallique chauffée ?

    Parce que la barre métallique conduit la chaleur loin du papier, empêchant sa température d'atteindre son point d'ignition.

  • Peut-on faire bouillir de l'eau dans un gobelet en papier sans le brûler ?

    Oui, l'eau permet de disperser la chaleur, empêchant le gobelet d'atteindre une température de combustion.

  • Pourquoi les thermomètres ont-ils généralement un bulbe cylindrique et non sphérique ?

    La forme cylindrique permet une mesure plus précise de la température en offrant une plus grande surface de contact avec le liquide à mesurer.

  • Pourquoi le verre est-il préférable au bois pour les cendriers ?

    Le verre conduit la chaleur loin, aidant à éteindre une cigarette oubliée.

  • Qu'est-ce qui se passe quand on chauffe une barre métallique avec des rayons en matériaux différents ?

    Les différents matériaux conduisent la chaleur à des vitesses différentes.

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    [Music]
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    um
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    [Music]
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    how do you do ladies and gentlemen and
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    boys and girls
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    i am julia sumner miller and physics is
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    my business
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    and my special business today is this
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    subject
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    the transfer of heat energy by the
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    mechanism of conduction
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    conduction very important word to know
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    the meaning of and i invite you
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    to look it up because its latin origin
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    is very important conduction consider
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    the following
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    an experiment which we will imagine
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    here are two rods
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    one is copper and one is iron and they
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    are fixed together very tightly at one
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    end and i am imagining that i am doing
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    the classical experiment that ben
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    franklin did on his investigation of
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    heat transfer by conduction we will
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    imagine that i put this junction in a
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    pot of hot oil
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    just like that
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    and i hold on to the remote ends of the
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    bar as i am doing
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    and lo and behold in a short while a
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    strange thing is witnessed one of these
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    feels hotter than the other and sooner
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    quicker
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    which means that one had thermal
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    conduction at a greater rate i invite
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    you to do this using a pot say of
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    boiling water and you will find a
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    strange thing that the conduction along
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    copper is about ten times as fast as a
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    long
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    iron of the same size rod consider
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    another wonderful experiment i'm going
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    to light my gas burner here which
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    perhaps i should have done already
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    there's the burner
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    now what do i have
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    i have two rods a shiny metal one and a
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    wooden one tightly fitted at a junction
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    here
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    now around that pair i have put a sleeve
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    of paper here is a wooden rod there is a
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    metal one and i've put that sleeve of
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    paper tightly on that junction
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    and i'm going to put this junction in a
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    flame of a gas tank gas burner and a
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    wonderful thing will happen
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    if
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    it does as i want it to do and if it
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    doesn't well then somebody says oh
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    professor the experiment failed but
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    experiments do not fail i must provide
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    nature exactly as she requires or she
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    won't do what i want her to do
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    i'm going to do it and watch now watch a
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    wonderful thing
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    a little
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    yes yes there it is there it is i want
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    the camera to get it tight
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    do you see
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    a very clearly bounded line
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    beautiful
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    and what do we find
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    that that paper scorched on the wood
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    side but not on the metal side why
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    because the metal is a good conductor
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    and it took the heat energy away
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    and did not allow time for the paper to
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    scorch
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    now next
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    beautiful thing here is a little paper
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    cup
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    i'm going to put a flame under that
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    paper cup
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    and as anyone in his right mind would
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    say professor that cup is going to burn
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    of course it's going to burn there it is
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    it's burning up it's burning up
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    as one would say its kindling
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    temperature was raised
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    no hurt
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    no hurt that's a pretty thing to see
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    though i like that look how nice and
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    shapely it still remains now what am i
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    going to do
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    i am going to fill another identical cup
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    with water
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    i'm going to fill a very same cup with
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    water
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    there it is right field and i'm going to
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    put this flame under that cup
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    and imagine what we will witness
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    we will witness this
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    that that water can be boiled in that
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    cup
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    without burning the paper cup except at
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    the rim where the paper is doubly or
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    triply folded and therefore very thick
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    so let's go on with some other matters
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    while we are waiting for that notice
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    your the housewife does not have to have
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    metal dishes to cook in she can cook in
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    a paper cup which is an idea for uh
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    conserving or conservation or something
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    let's look at that let's look at that
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    again
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    that water will shortly be boiling and i
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    can boil the water away
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    without burning up the cup
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    question regarding a thermometer
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    notice thermometer yes that's what it is
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    i have a thermometer question
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    supposing i had here a glass of very hot
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    water let's imagine you see imagination
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    i must emphasize that again wherever is
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    my pen
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    imagination
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    a very necessary ingredient of your life
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    and work especially if you're going to
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    be a physicist
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    here is a thermometer there is a glass
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    of hot water the thermometer reads the
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    room temperature at this moment
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    question i submerge it quickly into that
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    into that glass of hot water what do we
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    see first
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    very quickly first
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    answer not usually given
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    the answer is this there is a drop in
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    the reading of the thermometer it reads
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    less
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    why
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    because the glass bulb
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    was heated first by immersion in the hot
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    water the glass bulb expanded and the
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    mercury level dropped but now after a
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    while when the heat energy has been
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    conducted through the glass into the
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    mercury then up goes the level
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    one other question while i'm on a
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    thermal meter
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    why is the bulb cylindrical
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    cylindrical
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    cylindrical instead of spherical
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    why is it cylindrical
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    very good question so you notice my my
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    philosophy here people
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    teachers mothers fathers young and old
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    children
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    students
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    not to teach you any physics but rather
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    to show an abundance of demonstrations
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    which are enchanting and dramatic to
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    witness
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    let me consider oh
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    oh look here look here let's look at
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    that again the water is boiling
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    fearfully fast bubbling away and yet the
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    paper cup remains nearly with immunity
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    let's go on
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    here i have
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    a cigarette
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    let me light this cigarette
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    notice i don't know which end to light
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    but i'll light cigarettes
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    now i have done this already
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    i laid the cigarette on this wooden
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    block
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    and do you see what happened the wooden
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    block got scorched
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    we don't use wooden blocks for cigarette
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    uh for ashtrays we use glass for
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    ashtrays why because when the cigarette
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    if left to its own forgotten let us say
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    when the burning gets to the glass the
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    glass conducts the heat away
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    and
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    the cigarette probably will go out let
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    me illustrate that here is a beautiful
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    demonstration for you to do a fork and a
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    spoon
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    which i lodged together in this manner
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    and then i'm going to put
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    a match there
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    notice i try to work fast and probably
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    will get it all fouled up because i'm
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    working fast and here is another match
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    and watch what i'm going to do
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    watch
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    that's a beautiful thing notice how
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    stable that is
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    notice how stable that is that's
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    terrific
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    if we can get a tight shot right on that
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    right on that now i'm going to light
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    both matches
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    just give me your attention a minute
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    i'm going to light both matches
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    question what will happen
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    answer
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    i suggest nothing will happen
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    i suggest nothing will happen
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    why oh i'm sorry i blew out that match
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    and i shouldn't have done that
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    watch it
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    both matches will go out why this one
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    will go out when the flame reaches the
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    glass and that one will go out when the
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    flame reaches the spoon
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    well i hope it doesn't work and then
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    you'll say
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    well it did just uh just give me your
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    attention boys and girls and ladies and
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    gentlemen do you see it nearly didn't do
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    what i wanted it to do
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    and i heard you oh oh well it didn't do
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    what i wanted it to do
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    and i don't want you to say that the
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    experiment failed because it did not i
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    did not make the necessary provisions
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    for nature
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    all right
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    next question
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    beautiful for the housewives children
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    mothers fathers teachers
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    here are some small potatoes let's
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    imagine we have put them in the oven to
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    bake
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    and they are nearly all baked
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    dinner is about to be served and knock
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    knock knock some company
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    unannounced and may be unwanted you have
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    to make some potatoes quick for them and
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    all you have are some big ones
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    now you know these take very much longer
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    to bake than the small ones
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    you are not allowed to cut these but you
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    want them to bake quickly question how
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    will that be done
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    wonderful wonderful just take a couple
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    nails like this 80 penny spikes bang
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    like that
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    and
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    and bang like that
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    and two three more and put them in the
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    oven and are we not agreed that the
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    thermal conduction of this iron nail
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    will transfer the heat energy to inside
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    the potato and it will bake with all
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    quick dispatch
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    right or again
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    for people who eat flesh eaters
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    carnivorous human beings
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    question let me imagine that i have two
  • 00:10:16
    identical roasts of beef
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    absolutely identical in every respect
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    except that
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    one has a bone in it and the other does
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    not question
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    what is their rate of cooling uh cooking
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    when put in the oven answer
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    the one with the bone obviously will
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    cook the faster for very obvious reasons
  • 00:10:38
    is not bone a very good thermal
  • 00:10:40
    conductor indeed it is apart from that i
  • 00:10:44
    would like to lecture for about a half
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    an hour on the beautiful virtues that
  • 00:10:48
    this bone possesses
  • 00:10:50
    inside for example the marrow a blood
  • 00:10:53
    factory which keeps us going wonderful
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    thing so think more about the virtue of
  • 00:10:58
    a bone
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    or consider this
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    ho ho let's get back on there let's get
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    back on there
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    camera quickly get on the water in the
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    cup
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    the water is nearly all boiled out
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    and the cup is still not burning and i
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    say that's remarkable or
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    give me your attention for another
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    dramatic experiment here is an asbestos
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    glove
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    notice
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    notice
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    with absolute immunity why
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    oh i'll let that go because when all the
  • 00:11:29
    water is gone the obvious consequence
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    must ensue the paper then will reach its
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    kindling temperature and
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    conflagrate as one would say
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    another wonderful demonstration
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    thermal conduction
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    imagine that you get up in the morning
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    put your feet out of bed
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    and put your feet down
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    on the floor
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    do you not prefer to put your foot on
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    some deep heavy mattered stranded woolen
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    rug rather than on a bl bare floor
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    obviously why
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    consider the following
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    here i represent a bare floor
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    and here i represent a deep knife rug or
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    braided rug
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    i'm going to do as follows
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    right here and now
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    haha
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    feels cool
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    oh that feels warm
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    when in fact they are both at the same
  • 00:12:24
    temperature but this conducted the heat
  • 00:12:26
    away at a much more rapid rate and
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    therefore
  • 00:12:30
    it felt cooler
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    more than that illustration when you get
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    up in the morning if you don't have a
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    rug near the bedside what do you do
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    don't you turn your footsie woodsy on
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    the side sort of why to make less area
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    of contact so less heat energy will be
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    conducted away
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    the same thing happens here
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    i have a metal faucet i have a table top
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    i put my hand on the table top feels
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    warm
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    i put my hand on the faucet feels cold
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    oh no no no they are the same
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    temperature this however is a good
  • 00:13:05
    thermal conductor and took the heat
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    energy away
  • 00:13:10
    another remarkable demonstration
  • 00:13:14
    here it is
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    let's see oh yes yes notice i'm going to
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    show you
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    the water is nearly gone
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    but the paper cup has not burned let's
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    get on to this one
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    here is no i can't do it i don't think
  • 00:13:27
    here is a hub with some metal spokes all
  • 00:13:30
    different materials if i heat the metal
  • 00:13:33
    hub would i not find that the different
  • 00:13:35
    materials conduct the heat away at
  • 00:13:37
    different rates
  • 00:13:38
    so our show has been on the transfer of
  • 00:13:42
    heat energy by conduction and i thank
  • 00:13:45
    you for watching
  • 00:13:59
    oh
  • 00:14:09
    [Music]
  • 00:14:18
    you
Tags
  • conduction
  • physique
  • chaleur
  • expérience
  • énergie thermique
  • Julia Sumner Miller
  • matériaux
  • thermomètre
  • éducation
  • science