Julius Sumner Miller Lesson 5: Energy and Momentum

00:14:39
https://www.youtube.com/watch?v=4lC2bzXZq7I

概要

TLDRDans cette vidéo, Julius Suna Miller explique les concepts de l'énergie et de la quantité de mouvement en physique, en utilisant des démonstrations expérimentales pour illustrer ces notions. Il commence par démontrer comment deux voitures avec des masses différentes mais reliées par des élastiques montrent l'égalité des quantités de mouvement, malgré des énergies différentes dues aux distances parcourues. Miller explique ensuite l'importance de la friction dans les systèmes physiques, illustrant cela avec une boule sur une piste et un clou enfoncé dans du bois. Il présente divers types d'énergie, y compris mécanique, thermique, acoustique, et électrostatique, et souligne que les expériences scientifiques enseignent toujours quelque chose, peu importe le résultat. Des concepts sur la conversion d'énergie sont également explorés à travers plusieurs expériences pratiques, mettant en avant l'interaction entre force, distance, et travail en physique. Finalement, il aborde l'histoire des idées sur la quantité de mouvement et l'énergie, en mentionnant notamment les contributions de Christian Huygens et de Leibniz.

収穫

  • 🚗 Les forces sur deux voitures peuvent être égales, mais leurs énergies diffèrent.
  • ⚖️ La quantité de mouvement est l'un des concepts clés en physique.
  • 🌀 Les expériences démontrent la conversion de l'énergie mécanique en thermique.
  • 🔌 L'énergie électrostatique peut attirer la poussière inerte.
  • 💡 Plusieurs formes d'énergie incluant mécanique et thermique sont explorées.
  • 🍿 Le maïs éclate en raison de l'expansion extrême de l'eau intérieure.
  • 🎤 L'énergie acoustique est produite par les vibrations des cordes vocales.
  • 🔋 L'énergie potentielle peut être convertie en travail mécanique.
  • 📜 Histoire des concepts de l'énergie et du momentum avec Huygens et Leibniz.
  • 📚 Comprendre les différences entre énergie et quantité de mouvement est fondamental.

タイムライン

  • 00:00:00 - 00:05:00

    L'orateur, Julius Suna Miller, commence par intéresser son public au sujet de l'énergie et du moment en physique, en soulignant la différence cruciale entre ces deux concepts. Il explique que lorsque deux voitures connectées par un élastique sont séparées, l'énergie élastique est stockée. Une seule force agit sur les deux voitures, la petite voiture ayant une plus grande accélération et, par conséquent, acquérant une vitesse supérieure. Cependant, malgré l'équivalence des moments pour les deux voitures dues à l'inverse de la masse et de l'accélération, les énergies ne sont pas les mêmes puisque l'énergie est le produit de la force et de la distance parcourue.

  • 00:05:00 - 00:14:39

    Miller démontre ensuite les conceptions de l'énergie à travers divers exemples pratiques. En utilisant une piste courbe et une bille, il illustre comment l'énergie potentielle se transforme en énergie cinétique et perdue à travers le frottement et le son. Il démontre aussi le travail et la production de chaleur à travers le martelage de clous, et les divers types d'énergie, y compris mécanique, thermique et électrostatique, avec des démonstrations ludiques mais éducatives. Enfin, il aborde le principe de la conservation du moment et la distinction historique entre l'énergie et le moment, en mentionnant des figures historiques influentes comme le Français Alam et le Hollandais Christian Hens.

マインドマップ

Mind Map

よくある質問

  • Quels sont les types d'énergie mentionnés dans la vidéo ?

    Les types d'énergie mentionnés incluent l'énergie mécanique, thermique, acoustique, magnétique et électrostatique.

  • Comment la démonstration avec les voitures illustre-t-elle la quantité de mouvement et l'énergie ?

    La démonstration montre que même si les forces et les accélérations sont les mêmes pour les deux voitures, la quantité de mouvement est égale mais l'énergie est différente en raison des distances parcourues.

  • Pourquoi la boule ne peut-elle pas monter à la même hauteur après avoir roulé sur la piste ?

    En raison de la friction et de la génération de sons, la boule perd de l'énergie et ne peut pas retourner à la même hauteur d'où elle est partie.

  • Qu'est-ce qu'une expérience réussie selon Julius Suna Miller ?

    Une expérience est réussie lorsqu'on apprend quelque chose, même si on n'obtient pas le résultat initialement prévu.

  • Comment le clou illustre-t-il la conversion de l'énergie ?

    Le clou démontre la conversion de l'énergie mécanique en chaleur lorsqu'il est enfoncé dans le bois.

  • Qu'est-ce que l'expérience avec la tige en bakélite montre ?

    Elle montre l'énergie électrostatique en attirant de la poussière de CL après que la tige ait été frottée et chargée.

  • Quel phénomène physique est illustré par le jouet de l'ours en peluche ?

    Le jouet démontre le stockage et la libération d'énergie élastique.

  • Pourquoi la précision est-elle importante dans les expériences physiques ?

    La précision est essentielle pour que les démonstrations expérimentales fournissent des résultats attendus et significatifs.

  • Quel est l'effet de tenir un pistolet contre son épaule lors du tir ?

    Cela réduit la vitesse de recul car la masse globale (fusil plus épaule) augmente, réduisant ainsi le recul.

  • Comment la vidéo conclut-elle sur le sujet de l'énergie et de la quantité de mouvement ?

    Elle insiste sur l'importance de distinguer clairement entre ces deux concepts et invite à étudier leur histoire et développement.

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  • 00:00:00
    [Music]
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    how do you do ladies and gentlemen and
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    boys and girls I am Julius Suna Miller
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    and physics is my business and on
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    today's program our special business is
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    the subject of energy and momentum two
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    of the great immutable ideas of physics
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    and we must make clear their
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    difference so for my purpose I go to the
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    two cars again you remember what we have
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    in earlier programs a large massive
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    car on wheels and a smaller car Little M
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    on Wheels and they are on the tabletop
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    and they are connected by a sort of
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    elastic connection of rubber bands now
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    when I pull them apart I store some
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    elastic energy in the stretch
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    spring and there is a force then which
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    is exerted on both cars now what did we
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    learn before we learned that the big car
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    has a little acceleration and the little
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    car a big acceleration because one in
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    the same Force acts on both
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    cars now we also saw on another
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    occasion that the little car acquired
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    the greater
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    velocity and the bigger car the Lesser
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    velocity and we call the product of M
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    andv the
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    momentum and it is not unreasonable now
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    to say that because the accelerations
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    are inversely as the masses the
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    velocities are so and therefore the
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    momentum of the little
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    is equal to the momentum of the big car
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    so their moment are equal but now watch
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    watch is it not true that the smaller
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    car went the greater distance that is if
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    I let them come from a place of rest and
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    meet they would meet somewhere in here
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    this is the distance the big car would
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    go and this is the distance the little
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    car would go so the little car goes the
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    greater
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    distance s little s and now I Define for
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    you what is meant by work or energy in
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    physics the product of a force and a
  • 00:02:43
    distance the product of a force and a
  • 00:02:46
    distance so the same Force acts on both
  • 00:02:51
    cars but for the big car the distance is
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    a little one and for the little car the
  • 00:03:00
    distance is a big one and these products
  • 00:03:03
    are not equal so we learn this
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    astonishing thing that although the
  • 00:03:09
    forces are the same the accelerations
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    are inversely as the masses the
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    distances are inversely as the masses
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    the momenta are equal but the energies
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    are not very important idea now this
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    business of energy beautifully
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    demonstrated as follows look what we
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    have
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    here here is a curved
  • 00:03:37
    track straight and short here straight
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    and long
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    here now this end of the track is at the
  • 00:03:46
    very same elevation above the tabletop
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    as this end I have shimmed it up on that
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    end to get it
  • 00:03:54
    horizontal and what do we do we put a
  • 00:03:57
    ball at the top of this track at this
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    end it has so much potential energy
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    being so high above the zero potential
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    plane and I let it
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    go now it is losing some of its
  • 00:04:10
    potential energy gaining kinetic losing
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    energy really because friction is in the
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    system and we hear sound which costs the
  • 00:04:20
    ball something it cannot produce the
  • 00:04:22
    acoustic energy for nothing now what do
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    some think that coming down this long
  • 00:04:28
    track the ball down here will have
  • 00:04:32
    enough velocity enough kinetic energy of
  • 00:04:35
    motion to put it up over the track here
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    but that is not
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    so if the system were absolutely ideal
  • 00:04:44
    no friction at all which is impossible
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    the best the ball could ever do would be
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    to go to the same height here and since
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    we are in a real world and friction
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    plays a large role the ball can never go
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    as high on that end as I Let It Go from
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    on this end watch
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    it oh oh it did it did I'm glad it did
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    because I said it wouldn't so somebody
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    says Professor ah the experiment failed
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    no I think what I have done I uh
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    manipulated this end a little improperly
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    so that this end is higher and therefore
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    it did what it did so you see a lesson
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    to be learned learned experiments never
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    fail I'm going to lower this a little
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    and now I hope that this end is the same
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    height as that now watch
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    it oh that's it andless andless andless
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    and less and less and so on
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    until the energy of the system is spent
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    in friction and in producing sound and
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    in vibration
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    a very beautiful demonstration a device
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    which I call my energy track now let's
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    consider this business of energy further
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    here is a block of wood here is a nail I
  • 00:06:14
    drive the nail into the block of wood oh
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    says somebody what kind of physics is
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    that astonishing physics why I am doing
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    work on the nail the nail is doing work
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    on the wood to separate its particles
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    and when when work is
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    done when it is done against friction
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    forces heat energy always arises heat is
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    a necessary consequence of work done
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    against
  • 00:06:41
    friction proof I'm going to pull that
  • 00:06:45
    out what do I feel too hot too hot to
  • 00:06:48
    handle accordingly the work I did on the
  • 00:06:51
    nail has been commuted to
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    friction now there are several kinds of
  • 00:06:58
    energy several kinds which we need to
  • 00:07:02
    consider mechanical
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    energy mechanical
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    energy thermal
  • 00:07:09
    energy I just showed you that with the
  • 00:07:11
    with the uh the nail heated by driving
  • 00:07:14
    it
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    in while we're talking about thermal
  • 00:07:16
    energy here is some popcorn some popcorn
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    now you know that if you apply thermal
  • 00:07:22
    energy to the popcorn it soon as a
  • 00:07:25
    result of this application of thermal
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    energy of heat explode
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    why because we gave energy to the little
  • 00:07:33
    little bit of water in the droplet in
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    the kernel of corn it expanded
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    enormously how many times does it expand
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    fantastic 1,700 times isn't that
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    fantastic no wonder the colonel explodes
  • 00:07:47
    with a rupturing Force mechanical energy
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    thermal energy acoustic
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    energy sure my vocal cords are in
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    vibration and that's the only reason you
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    can hear me I am giving ra R to
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    excitation of the air in this place and
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    it is falling on your eardrum and
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    putting your ear drum into motion and
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    then the bones in the ear and finally
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    the impulse gets to your
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    brain acoustic uh magnetic
  • 00:08:14
    energy electrostatic energy
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    electrostatic let me show you that
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    because it is absolutely exciting watch
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    this watch I have here some CL dust
  • 00:08:26
    which I put out on the table CL dust
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    it is lifeless and dead and inert here
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    is a bakerite hard rubber Rod now the
  • 00:08:37
    rod I say and later we will say more
  • 00:08:40
    about it on a program on electrostatics
  • 00:08:42
    the rod is electrostatically neutral I
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    bring it near the CL
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    dust and what do I see happen answer
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    nothing seeing nothing happens is a very
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    important thing to see very
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    important now I am going going to do
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    some work on this rubber Rod work work
  • 00:09:05
    now watch oh Mama Mia look at that the
  • 00:09:10
    COA dust has been attracted to the rod
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    not only that but it's jumping off it's
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    jumping
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    off and would you believe it this is the
  • 00:09:20
    foundation of all of our electric
  • 00:09:23
    science indeed these television cameras
  • 00:09:26
    could not work were this principle not
  • 00:09:30
    uncovered more about energy more energy
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    energy here is a massive
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    weight which I have lifted above the
  • 00:09:40
    level of the floor the zero potential
  • 00:09:42
    plane I am doing some mechanical work on
  • 00:09:45
    it I am endowing it with potential
  • 00:09:47
    energy here is a nail in a block of wood
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    and I release the
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    weight look what has happened it has
  • 00:09:56
    driven the nail into the block
  • 00:09:59
    the heat developed here very
  • 00:10:02
    substantial a toy energy a toy a
  • 00:10:07
    spring if I do work on the spring I
  • 00:10:11
    store energy in the spring there is a
  • 00:10:14
    so-called suction cup on the bottom and
  • 00:10:17
    in another program I will show you that
  • 00:10:20
    that word suction is not a good one ever
  • 00:10:23
    to use but I'm going to put a ball in
  • 00:10:26
    this upper
  • 00:10:28
    platform p push down the spring storing
  • 00:10:32
    some energy in the compressed spring now
  • 00:10:35
    the energy is available to do work for
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    me on the ball when the atmospheric
  • 00:10:42
    pressure seeps into that so-call suction
  • 00:10:46
    cup it will let the spring loose and you
  • 00:10:49
    know the consequence up will go the ball
  • 00:10:52
    there it goes up went the ball and there
  • 00:10:54
    was something else there was some action
  • 00:10:57
    taking place in this Pro projectile
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    mechanism which Bears also on momentum
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    and
  • 00:11:04
    energy consider this business of
  • 00:11:07
    momentum this gun is a toy and so we
  • 00:11:11
    need have no fear about it but don't
  • 00:11:13
    play with guns concerning
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    momentum if I shoot the gun holding it
  • 00:11:19
    far from my shoulder will it not kick
  • 00:11:22
    very severely and hurt me why the mass
  • 00:11:25
    of the gun recoils with a certain
  • 00:11:28
    velocity the M and the v constituting a
  • 00:11:31
    certain momentum how do you avoid this
  • 00:11:34
    kick you hold the gun tightly against
  • 00:11:37
    your shoulder so that when the gun
  • 00:11:40
    recoils you and the gun constitute a
  • 00:11:43
    larger mass and therefore less recoil
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    velocity an excellent demonstration of
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    momentum
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    conservation consider a toy made for
  • 00:11:55
    threey olds here is a little toy
  • 00:12:00
    a uh a uh a teddy bear mounted on an
  • 00:12:04
    elastic shaft through his shoulders he
  • 00:12:07
    stands in a vertical plane because his
  • 00:12:09
    center of gravity is below his axis of
  • 00:12:11
    support and now what am I going to
  • 00:12:15
    do I rolled him away and he rolls back
  • 00:12:19
    and so I am demonstrating a profound
  • 00:12:22
    principle of physics in a toy for twoy
  • 00:12:26
    olds we stored some elastic energy it
  • 00:12:29
    was now available to do work on me to
  • 00:12:32
    return the car or such a toy an array of
  • 00:12:37
    geared wheels and a
  • 00:12:39
    shaft and some uh uh seers in there
  • 00:12:43
    which rub against other things and
  • 00:12:45
    produce heat from friction and
  • 00:12:49
    notice I am showing the transmutation of
  • 00:12:53
    mechanical work into thermal energy as
  • 00:12:56
    well as into light because when body get
  • 00:13:00
    hot enough they become
  • 00:13:04
    incandescent energy momentum very
  • 00:13:08
    important now as one views the history
  • 00:13:10
    of this subject I invite you to study it
  • 00:13:14
    yourself because for 150 years there was
  • 00:13:19
    much
  • 00:13:20
    dispute on the difference between
  • 00:13:23
    MV and MV
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    Square which were settled by by a
  • 00:13:29
    Frenchman named Alam but who gave rise
  • 00:13:32
    to the problem in the first place a
  • 00:13:35
    young Dutchman by the name of Christian
  • 00:13:37
    hens and I want to show you a picture of
  • 00:13:41
    him as a little boy at the age of 11 an
  • 00:13:45
    enchanting little rascal and I shall
  • 00:13:47
    have more to say about him sometime on a
  • 00:13:49
    program on light because he spent his
  • 00:13:52
    youthful youthful days throwing pebbles
  • 00:13:55
    into the canals in his native Holland
  • 00:13:57
    and watching the ever growing Circles of
  • 00:14:00
    disturbance and thus was led to the idea
  • 00:14:03
    of the wave motion of light and here
  • 00:14:06
    finally is a picture of him in his later
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    days with his with his uh what shall we
  • 00:14:14
    call it
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    wig now the idea of momentum must be
  • 00:14:19
    clearly distinguished from the idea of
  • 00:14:22
    energy and I thank you for your
  • 00:14:28
    attention
  • 00:14:38
    the
タグ
  • énergie
  • momentum
  • physique
  • friction
  • démonstration
  • expériences
  • électrostatique
  • conversion d'énergie
  • types d'énergie
  • Julius Suna Miller