Julius Sumner Miller: Lesson 10 - Atmospheric Pressure

00:14:38
https://www.youtube.com/watch?v=uOhm6ryOHI4

Zusammenfassung

TLDRDans cette vidéo, le professeur Julia Sumner Miller présente plusieurs démonstrations captivantes sur la pression atmosphérique. Il commence par chauffer de l'eau dans une boîte métallique, puis montre que lorsque la vapeur d'eau se condense, la pression à l'intérieur du récipient diminue, entraînant l'effondrement de la boîte sous la pression atmosphérique. Il utilise également une pompe à vide pour réduire la pression à l'intérieur de divers objets, illustrant l'énorme force de la pression de l'air. D'autres expériences incluent l'usage de ventouses, démontrant que ce n'est pas la "suction" qui les maintient ensemble mais bien la pression extérieure de l'air. Il montre comment la pression atmosphérique joue un rôle crucial dans la vie quotidienne, et conclut avec une explication des baromètres et des altimètres, des instruments mesurant la pression de l'air pour indiquer les changements d'altitude et de météo.

Mitbringsel

  • 🛢️ La pression atmosphérique est démontrée en chauffant une boîte métallique.
  • 🔊 L'air pousse avec une force incroyable, environ 15 livres par pouce carré.
  • 🌊 Enverser de l'eau froide sur la boîte augmente la condensation de la vapeur.
  • 💨 Une pompe à vide montre comment l'air peut écraser des objets.
  • ⚖️ 15 lb/pouce carré se traduisent par 45 000 lb sur un corps humain.
  • 🔧 Les ventouses démontrent l'effet de la pression de l'air plutôt que la suction.
  • 📐 Un altimètre mesure l'altitude en fonction de la pression.
  • 🌡️ Les baromètres mesurent la pression atmosphérique pour prédire la météo.
  • 🐦 L'air est essentiel pour le vol des oiseaux et des avions.
  • 🧪 La science de l'air est essentielle pour comprendre des phénomènes quotidiens.

Zeitleiste

  • 00:00:00 - 00:05:00

    Julia Sumner Miller présente une expérience en physique pour démontrer les effets de la pression atmosphérique à l'aide de boîtes de conserve, d'eau bouillante, et de nourriture sous vide. Elle chauffe une boîte de conserve contenant de l'eau jusqu'à ébullition, puis retire la chaleur et scelle la boîte. En refroidissant la vapeur d'eau se condense, créant une pression plus basse à l'intérieur, permettant à la pression atmosphérique d'écraser la boîte. Elle explique que cela se produit parce que la pression atmosphérique est plus forte à l'extérieur qu’à l'intérieur de la boîte condensée, et elle accélère le processus en versant de l'eau froide pour illustrer visuellement la force étonnante exercée par la pression de l'air sur la boîte.

  • 00:05:00 - 00:14:38

    Elle poursuit l'expérience en utilisant une pompe à vide pour démontrer davantage la pression de l'air avec des objets divers, notamment un morceau de pneu en caoutchouc et des hémisphères de Magdebourg, expliquant que la pression atmosphérique est responsable de leur maintien ensemble et non une force de "suction". Elle mentionne l'invention de la pompe à vide par Otto von Guericke et montre des illustrations de son fonctionnement historique. Julia termine en illustrant l'immense poids de l'air qui nous entoure, en reliant cela à un manomètre anéroïde, et explique comment cela contribue à la mesure de l’altitude et aux changements météorologiques. Elle conclut en réitérant la puissance impressionnante de la pression atmosphérique sur divers objets et son immense impact sur la vie quotidienne.

Mind Map

Mind Map

Häufig gestellte Fragen

  • Quelle est la force de la pression atmosphérique ?

    La force exercée par l'atmosphère est d'environ 15 livres par pouce carré.

  • Quel est le but de l'expérience avec le bidon en métal ?

    Il s'agit de démontrer la force de la pression atmosphérique sur un bidon en métal par la condensation de vapeur.

  • Combien pèse l'air qui pèse sur un être humain ?

    L'air exerce une pression de 45 000 livres sur une personne de taille moyenne.

  • Comment un altimètre mesure-t-il l'altitude ?

    Un altimètre utilise un système de levier et mesure la pression atmosphérique pour indiquer l'altitude.

  • Que se passe-t-il lorsque la pression diminue dans un récipient fermé ?

    L'air est comprimé quand la pression diminue dans un récipient, ce qui fait s'effondrer les structures fragiles sous la pression extérieure.

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Untertitel
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Automatisches Blättern:
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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'm julia sumner miller and physics is
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    my business and our business today has
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    more than ordinary enchantment and i
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    will go at once to it consider the
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    following
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    i have a tin can
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    with some water in it
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    under which i have put a burner
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    so that the water has now been boiling
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    for a time as evidenced by the water
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    vapor seen here condensed and we call it
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    steam
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    so that what remains in the vessel now
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    is some water less than before and some
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    water vapor
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    now i'm going to take the burner away
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    and stop her up
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    the can
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    and we will witness an astonishing and
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    absolutely astonishing thing
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    if we listen very carefully we will hear
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    a certain flexing of the can
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    what is happening some of the water
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    vapor is condensing the pressure is
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    getting less in the can and the
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    atmosphere is taking hold and
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    atmospheric pressure is an astonishing
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    thing
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    i will hasten the process by pouring
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    some cold water on it and this is an
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    experiment you can do with absolute
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    enchantment yourself
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    here it is
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    i am going to take the burner away
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    i am going to stop this up
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    i'm going to put it down here
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    listen
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    oh
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    oh but watch it i'll hasten the process
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    [Music]
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    oh there it is let me turn it around
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    there it is and i say that is something
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    to bear witness to that is fantastic the
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    push of the air
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    staggering
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    in its consequences for the human race
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    now listen listen
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    the water is boiling inside that can at
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    reduced pressure
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    at a much lower temperature than 100
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    degrees centigrade because the pressure
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    inside is less than one atmosphere
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    this is fantastic
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    fantastic
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    let me show it to you another way
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    here i have another tin can
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    and i'm going to connect this tin can to
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    a vacuum pump which permits me to pump
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    out some of the air
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    and just a little of it i could never
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    pump it all out if i pump for a million
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    years i couldn't get it all out why too
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    many molecules in there but let me
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    there it is
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    there it is
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    there it is the push of the air
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    staggering to witness staggering
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    show it to you another way
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    take a look at another piece of
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    apparatus i have a funnel
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    a funnel
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    and across the top of it is a sheet of
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    rubber tubing as from an automobile
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    inner tubing
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    the air inside is at atmospheric
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    pressure i'm going to connect the vacuum
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    pump here and reduce the pressure inside
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    from atmospheric less and less and less
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    and less
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    and the rubber sheet
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    suffering the forces the push of the air
  • 00:03:28
    will be depressed inside deeper and
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    deeper and deeper
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    and indeed
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    if it can endure the reduction in
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    pressure and the push of the atmosphere
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    i shall be surprised very likely it will
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    be
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    be
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    torn apart here it is there's the rubber
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    tube i am going to
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    connect this
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    now i'm going to reduce the pressure
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    there it is getting pushed in
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    there it is getting pushed in
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    oh man this is something
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    i'm going to stop in a minute let's get
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    a tight shot if you will of that and
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    notice notice the enormous push of the
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    atmosphere fantastic
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    now i'm going to evacuate more and more
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    and let the push of the air push that
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    more and more and i'm going to step
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    aside because when this does indeed
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    burst it has a detonation which could
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    well unseat this building
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    that'd be very good
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    oh i like to do this once in a while
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    because it adds to the drama of the
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    matter it adds to the drama oh there it
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    went
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    there it went i hadn't expected it
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    really but notice the enormous forces of
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    the air
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    how enormous
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    well only about 15 pounds per square
  • 00:05:06
    inch at sea level
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    let me remind you of the consequences
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    the ordinary human being has about three
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    thousand square inches of surface three
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    thousand square inches of surface
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    three thousand square inches
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    if you skinned an ordinary human being
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    laid out the skin and measured the
  • 00:05:24
    projected area be about that on every
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    square inch there's about 15 pounds
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    45 000 pounds is the push of the air on
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    me
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    40 over 20 tons is there any wonder why
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    at the end of the day a fella goes
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    around all worn out carrying that load
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    of air
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    now to show you further the consequences
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    consider these things
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    which we need to look at sharply
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    acutely circumspectly because what is
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    said about them is always wrong
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    they are called suction cups
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    suction cups
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    and i must advise you to put the word
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    suction
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    out of your vocabulary it is
  • 00:06:09
    unacceptable
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    why because there is no suction no such
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    force
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    what do we do let me squeeze them
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    together face upon face and what have i
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    done
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    i have squeezed the air out from between
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    them
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    now why are they held together
  • 00:06:27
    they are held together because of the
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    push of the air
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    i could compute it very readily if i let
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    us say i have squeezed out all the air
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    inside
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    from between them
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    all i need to do is measure their area
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    pi r square is the area of a circle
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    and that area in square inches times 15
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    pounds per square inch indeed it turns
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    out that about 300 pounds is necessary
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    to pull these apart
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    about 300 pounds necessary to pull them
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    apart of course look at the usefulness
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    look at that
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    indeed regarding the usefulness the next
  • 00:07:03
    time you watch
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    people who change big panes of glass in
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    department store windows you will notice
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    the pane of glass weighs half a ton and
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    three four men carry it how by by fixing
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    a
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    so-called
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    forgive me for the use of the language
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    so-called suction cups and then they
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    carry it around
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    the push of the atmosphere
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    now i use the vacuum pump in this
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    and you should read
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    about otto von garaki
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    g-u-e-r-i-c-k-e
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    who in the 16th century
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    invented the vacuum pump
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    and i want to show you his first one
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    if we can get a tight shot of that
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    there we are notice here is a pump with
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    a piston and two men are drawing on it
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    and he reports in his report to the
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    societies and scientific societies that
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    there was first a slight hissing as by
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    bees and birds and then bang
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    the cast collapsed here is another one
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    showing the same
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    fantastic
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    those two hemispheres put together
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    the original magdeburg hemispheres and
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    here is a picture of von
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    so we should pay him tribute
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    we should pay him tribute
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    now i have spoken the magdeburg
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    hemispheres let's take a look at them
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    here they are in replica
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    two hemispheres made of steel which i
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    put closely face to face
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    and then i connect the vacuum pump
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    and the valve is open
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    and i take out some of the air
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    i take out some
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    never all could never take it all out
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    then i'm going to close the valve
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    shut off the pump
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    now i'm going to try to pull them apart
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    never not one man alone indeed two could
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    hardly do it so i'm going to do
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    something obviously the pressure inside
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    is too low the push of the atmosphere
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    outside is too big
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    i'm going to
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    do something watch listen listen i'm
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    going to open the valve instantaneously
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    there
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    now what did i do
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    oh some say you let some of the vacuum
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    out
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    oh that murders me
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    as macbeth murder sleep didn't let any
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    of the vacuum out i'll let some air in
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    still too much
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    let more of the vacuum out
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    oh now i let so much out that all of
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    it's out and so we have the magdeburg
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    hemispheres a classical demonstration
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    historically
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    of atmospheric pressure
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    one more very dramatic one on an earlier
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    program i showed this when i talked
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    about inertia but i want to do this now
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    because it is a demonstration of
  • 00:10:05
    atmospheric pressure
  • 00:10:07
    you see
  • 00:10:08
    ladies and gentle boys and girls what i
  • 00:10:10
    am trying to do is not teach any physics
  • 00:10:12
    in these recitations but rather stir
  • 00:10:15
    your interest by events which are
  • 00:10:16
    dramatic for the soul here is a sheet of
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    paper
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    about 20 inches one way and 30 the other
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    600 square inches on each square inch 15
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    pounds 600 times 15 9 000 pounds of air
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    and you know as i did before i'll do it
  • 00:10:33
    once again
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    i cannot move the weight of that air
  • 00:10:38
    there it is
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    and i say that is staggering to
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    contemplate the push of the air
  • 00:10:45
    of what usefulness is this oh well
  • 00:10:48
    without air birds couldn't fly and
  • 00:10:49
    airplanes couldn't fly
  • 00:10:51
    indeed talking about flying
  • 00:10:53
    here is an instrument called an
  • 00:10:56
    altimeter altimeter
  • 00:10:58
    what does it consist of
  • 00:11:00
    it considers which is highly evacuated
  • 00:11:03
    i'll draw that little chamber which is
  • 00:11:05
    highly evacuated here it is
  • 00:11:09
    highly evacuated and it has a lever
  • 00:11:11
    system on it with a scale
  • 00:11:13
    now
  • 00:11:14
    we go
  • 00:11:15
    high into the sphere very high ends a
  • 00:11:18
    little
  • 00:11:19
    the cover lifts up and leave on so we
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    get a reading of the athode terms of the
  • 00:11:24
    air
  • 00:11:26
    or if you wish another use
  • 00:11:29
    made of the atmosphere which has so much
  • 00:11:32
    to do with the events of weather
  • 00:11:34
    here is an aneroid barometer which has
  • 00:11:37
    inside it exactly the same thing
  • 00:11:40
    the response of the chamber
  • 00:11:43
    to increase and diminution of pressure
  • 00:11:45
    gives rise to a reading and i advise you
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    invite you to look up the word aneroid
  • 00:11:52
    because what does it mean
  • 00:11:54
    it means without a meaning not and near
  • 00:11:57
    us
  • 00:11:58
    wet without wetness so it is not a
  • 00:12:01
    mercury in glass barometer but a dry
  • 00:12:04
    barometer and talking about a mercury
  • 00:12:06
    and glass barometer here's something you
  • 00:12:08
    can do take a long glass tube about a
  • 00:12:11
    meter long
  • 00:12:12
    and fill it with mercury
  • 00:12:15
    it's closed at one end
  • 00:12:17
    closed at one end fill it with mercury
  • 00:12:19
    then take a vessel in which the mercury
  • 00:12:22
    resides
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    turn the tube upside down a finger
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    across the open end
  • 00:12:27
    immerse submerge the open end in this
  • 00:12:30
    vessel of mercury and take your finger
  • 00:12:32
    away remember the tube is filled with
  • 00:12:33
    mercury
  • 00:12:35
    what would you expect you would expect
  • 00:12:37
    all the mercury to fall out
  • 00:12:40
    no it does not it's to a certain level
  • 00:12:43
    and notice the shape of the meniscus the
  • 00:12:46
    shape of the surface
  • 00:12:47
    it for
  • 00:12:49
    how far so that this length is about 76
  • 00:12:52
    centimeters or about 30 inches
  • 00:12:56
    and that is one atmosphere which
  • 00:12:58
    sustains this column of mercury and here
  • 00:13:01
    is a region
  • 00:13:03
    highly highly empty of everything except
  • 00:13:06
    a little mercury vapor perhaps
  • 00:13:10
    so one of the best vacuums we can get is
  • 00:13:13
    produced by such a performance of a
  • 00:13:15
    mercury column in a glass tube
  • 00:13:19
    now let's see what else we could show
  • 00:13:22
    what else could we look at this isn't
  • 00:13:24
    this fantastic indeed
  • 00:13:27
    i have another one i have another one
  • 00:13:29
    and since it enchants me i'm going to do
  • 00:13:31
    it this was boiling over there here it
  • 00:13:33
    is
  • 00:13:35
    notice
  • 00:13:36
    notice
  • 00:13:37
    i'm in a hurry
  • 00:13:39
    listen
  • 00:13:45
    there it goes
  • 00:13:47
    notice i thought i had not boiled the
  • 00:13:49
    water long enough because if there was
  • 00:13:50
    any occluded air in there we would have
  • 00:13:53
    trouble and so are you not agreed that
  • 00:13:55
    atmospheric pressure is a staggering
  • 00:13:57
    thing to witness and i thank you for
  • 00:13:59
    listening
  • 00:14:02
    [Music]
  • 00:14:37
    you
Tags
  • pression atmosphérique
  • expérimentation physique
  • vapeur d'eau
  • boîte métallique
  • vacuum pump
  • altimètres
  • baromètres
  • démonstration scientifique
  • physique
  • Julia Sumner Miller