How Special Relativity Makes Magnets Work

  • Опубликовано:  3 года назад
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    Magnetism seems like a pretty magical phenomenon. Rocks that attract or repel each other at a distance - that's really cool - and electric current in a wire interacts in the same way. What's even more amazing is how it works. We normally think of special relativity as having little bearing on our lives because everything happens at such low speeds that relativistic effects are negligible. But when you consider the large number of charges in a wire and the strength of the electric interaction, you can see that electromagnets function thanks to the special relativistic effect of length contraction. In a frame of reference moving with the charges, there is an electric field that creates a force on the charges. But in the lab frame, there is no electric field so it must be a magnetic field creating the force. Hence we see that a magnetic field is what an electric field becomes when an electrically charged object starts moving.

    I was inspired to make this video by Prof. Eric Mazur

    Huge thank you to Ralph at the School of Physics, University of Sydney for helping us out with all this magnetic gear. Thanks also to geology for loaning the rocks.

    This video was filmed in the studio at the University of New South Wales - thanks to all the staff there for their time and support.

    Music: Firefly in a Fairytale, Nathaniel Schroeder, and Love Lost (Instrumental) by Temper Trap licensed from
  • КатегорииОбразование
  • Длительность: 4:19
  • Тэги для этого Видео:  veritasium  science  physics  magnet  magnets  magnetic  how do electromagnets work?  how do magnets work?  special relativity  length contraction  attract  repel  minutephysics  charged cat  

Комментарии: 4 140

  • Martin Ducharme
    Martin Ducharme 13 часов назад

    I really like cooperative videos between youtubers.

  • Benjamin Lehmann
    Benjamin Lehmann 19 часов назад

    Best, most mind blowing video I've seen on YubTubs for a year.

  • José B. Junior
    José B. Junior 1 день назад

    Einstein still blowing my mind.

  • Caue Rego
    Caue Rego 3 дня назад

    what would happen to physics if instead of using cats to explain theories they'd use armadillos?

  • kristoffer gaard
    kristoffer gaard 4 дня назад

    I hope somebody can answer this question:

    According to special relativity, objects moving relative to one-another are subject to length contraction. So when the cat is static and the electrons in the wire start moving, wouldn't the electrons be subject to length contraction? Thus creating a higher density of electrons thus attracting the kitty?

  • ski
    ski 4 дня назад

    I really think a video about drift velocity would clarify this topic even more so than this excellent clip already does.

  • kdmc40
    kdmc40 4 дня назад

    Ah! This explains why I'm attracted to my sister-in-law! I knew it wasn't my fault!

  • Sean Dafny
    Sean Dafny 5 дней назад


  • Sean Dafny
    Sean Dafny 5 дней назад

    Thank u so much Feynman

  • SillieWous
    SillieWous 6 дней назад

    In the stationary cat case: why is the cat not attracted to the wire? Moving electrons would be more densely packed, thus overall negative charge and hence the cat should be attracted.

  • Gor O
    Gor O 8 дней назад

    it's a shame. delete this video

  • ​ ​
    ​ ​ 9 дней назад

    For anyone that came there trought the question "Why is magnetic force perpendicular to current/charge velocity/magnetic field?", this video perfectly explains.

  • chari Muvilla
    chari Muvilla 10 дней назад

    So when the electrons are moving it is like there are more of them everywhere?! Lol I'm never gonna understand how magnets work. Stupid world

  • Nikhil Aggarwal
    Nikhil Aggarwal 10 дней назад

    why not non-moving cat is attracted to wire?

  • Diluksh Fernando
    Diluksh Fernando 11 дней назад

    0:45 Adolf Hitler

  • Rober oat
    Rober oat 14 дней назад

    So how does this attract ferromagnetic stuff

  • Name_less
    Name_less 14 дней назад

    So if I'm moving fast enough i could occupy less space that someone who is stationary, what if blackholes are just moving really fast therefore taking up much more space than they seem to be, so it can look like they are squeezing matter into a fixed position to make a really strong gravitational force, but they are really just spinning really fast.

  • Minecraftster148790
    Minecraftster148790 15 дней назад

    Does this mean you can determine the speed of light using an electromagnet?

  • Ido Ben Lulu
    Ido Ben Lulu 15 дней назад

    why the density of the electron proton be the same if the electons move ? Dont the electons suppose to cover less space and hence the wire would be negatively charge from Vertasium reference? why only when the protons "move" the density isnt the same?

  • Samantha Kun
    Samantha Kun 16 дней назад

    kawaii cat <3

  • Jack 'o Bong
    Jack 'o Bong 16 дней назад

    this video shows how magnets are RELATED to RELATIVITY

  • Johnny Pacheco
    Johnny Pacheco 17 дней назад

    I think you mix thinks together which have nothing to do with one another.....

  • Sam Sırri
    Sam Sırri 18 дней назад

    02:13 this cat has a badly inflamed tooth root :(

  • Victor Drevin
    Victor Drevin 20 дней назад

    So an electron only moves about three centimetres per second?

  • Ajas Azeez
    Ajas Azeez 22 дня назад

    how the attraction between an iron piece and an electro magnet relatively at rest can be explained by the same theory

    • Sam Sırri
      Sam Sırri 18 дней назад

      the electrons are still moving in the wire.

  • onehit pick
    onehit pick 22 дня назад

    A positive cat experiences forces with a neutral wire with no current, including gravitational and electromagnetic forces. Your opening statements contradict the simplest of experimental observations and the most fundamental of theories. Try rubbing a balloon on your hair and see how it interacts with nearby mostly neutral objects, including ceilings, wire strands, etc...

  • martiarenax3
    martiarenax3 23 дня назад

    Bad. From this point of view the electromagnets should be purely one negative field and it's not so.

  • Joebert
    Joebert 23 дня назад


  • Prince 1022
    Prince 1022 25 дней назад

    why is special relativity true ?

  • Hebert Sanchez
    Hebert Sanchez 26 дней назад

    I am in an infinite magnetic loop between veritasium and minute physics. :(

  • Lars Berntzon
    Lars Berntzon 27 дней назад

    Can you explain how the magnetic spin of the electrons comes into play for the relativistic effect? I don't understand this.

  • Ariel Nicolai
    Ariel Nicolai 27 дней назад

    Very interesting!. The example is understood. but now, someone can explain me what happen if the cat stays still?
    1. If I think the example using the traditional phisics: the cable makes a magnetostatic field and the cat doen't experiment a force because its velocity is null.
    2. But if I think the example using the relativistic phisics: the electrons are moving into the cable, so the cat sees that the electrons are closer each other because the contraction of lenght. So, the resultant charge is negative (if I close a section the cable in a volume) giving an electric resultant field and so, a resultant electrical force in the cat ponting to the cable...

    Please help me, because I can't stop thinking! jajaja

  • StoneBacon
    StoneBacon 27 дней назад

    Holy crap! What a beautiful and simple explanation. The "only in your frame of reference was hilarious" 10/10

  • Ariel Nicolai
    Ariel Nicolai 28 дней назад

    Dear veritasium, what is the name of the music in background???

  • Ashwini Kumar
    Ashwini Kumar 29 дней назад

    Why is there no force on cat when only current is flowing through the wire?
    electrons are flowing relative to the cat , so it should contract as it is moving.
    And hence the wire should be more negative and cat should get attracted towards the wire.

  • Marcus Tornea
    Marcus Tornea 29 дней назад

    For the cat's stationary frame, the electrons should be denser therefore it should attract the cat. But for the electron's frame, the positive charges are denser; therefore it shouldn't attract the stationary cat. For the cat's moving frame, the positive charges look denser; therefore it repels the cat, but for the positive charges' frame, the electrons look denser and therefore should instead attract the moving cat. Knowing that relativity states that all perspectives are considered valid, I personally disagree with this theory.

  • Shubham Dhiman
    Shubham Dhiman 29 дней назад

    mind = blown !
    why is this not taught in relativity courses?

    • Shubham Dhiman
      Shubham Dhiman 28 дней назад

      0MoTheG of course that is taught but the fact that SR unites electricity and magnetism isn't even mentioned

    • 0MoTheG
      0MoTheG 28 дней назад

      The Lorentz transformation is taught in every course that includes SRT.

  • Shree Vignesh
    Shree Vignesh 29 дней назад

    So if there is a stationary positive charge outside the wire it gets attracted when current passes through the wire??

    • 0MoTheG
      0MoTheG 28 дней назад

      Strangely no.

  • Rakibul Islam Prince
    Rakibul Islam Prince 29 дней назад

    yesssssssssssssssss..........i got it........
    thanks bro...................thank u very much

  • Vishal Shah
    Vishal Shah 29 дней назад


  • breakingthemasks
    breakingthemasks 1 месяц назад

    never commented here before...but this video and it's twin were stellar. more high level videos! great job🖒

  • Crafty DIY Craftlantic
    Crafty DIY Craftlantic 1 месяц назад

    what if the positively charged cat moved the one way when the negatively charged atoms in the wire went the other way ?

  • Alexander Dräbenstedt
    Alexander Dräbenstedt 1 месяц назад

    So does an electron beam, which is a current without surrounding protons, not produce a magnetic field? I would doubt that.

  • Ryan Koepke
    Ryan Koepke 1 месяц назад

    what is the positive "cat" was moving near the speed of light? What would that do to the charge?

  • makro80
    makro80 1 месяц назад

    How does the cat near the neutral wire at 3:00 get pushed away? Like he said in the video its due to the magnetic field around the wire but I dont understand how that would cause it to be repelled?

  • nikitha nayaer
    nikitha nayaer 1 месяц назад

    mind = blown
    oh and how did you assume the cat was female what if it identified it's self as a helicopter

  • Cat Man
    Cat Man 1 месяц назад

    The best explanation I've seen for electromagnets

  • Engineer Ahmad
    Engineer Ahmad 1 месяц назад

    Direction of Magnitic field is tangent to conductor not away from it

  • Kyle MacDonald
    Kyle MacDonald 1 месяц назад

    How do you grow such a thick beard in six hours? Takes me a week and a sacrifice to the eldritch follicular powers.

  • peanutaxis
    peanutaxis 1 месяц назад

    The velocity of an electron in a 2mm radius wire with 1 ampere flowing throuogh it is:


    .....and I'm supposed to believe that relativistic effects are relevant. I don't *&%ing think so.

    wiki: Drift_velocity#Numerical_example

  • erikk77
    erikk77 1 месяц назад

    Thank you Michael Faraday.

  • Dercio Silveira
    Dercio Silveira 1 месяц назад

    I dreamed that a moving charged particle affect some quantum field like plane´s wings, creating lifting (magnetisim)...

  • Cold Death By Multiverses
    Cold Death By Multiverses 1 месяц назад

    This all sounds more like a classic interpretation rather than a relativistic one, because only Galilean Relativity was used to explain it.

  • deltango12345
    deltango12345 1 месяц назад


  • Mike Billars
    Mike Billars 1 месяц назад

    This doesn't make sense to me. I always thought that electrons actually move *very* slowly through a conductor - like millimeters per second. If that's true, then the Lorentz contraction would be so insignificant that I can't imagine it having any effect at all. What am I missing?

  • Lu Chee Ket
    Lu Chee Ket 1 месяц назад

    What consequent can we tell when a high power transformer is performing in a strong electrostatic field?

  • Lu Chee Ket
    Lu Chee Ket 1 месяц назад

    Right hand screw rule is best to rely and consequently charges appear with relative motion induce equal charges to flow in opposite direction as equivalence to magnetic's in or out for determination of force direction.

  • Lu Chee Ket
    Lu Chee Ket 1 месяц назад

    The prevailed +dQ to moving +q repels, and the prevailed -dQ to moving +q attracts with opposite current seems to be logically right.

  • AvioPhile
    AvioPhile 1 месяц назад

    That is pretty, then in all reference frames we agree on the end result. How does it fit with electromagnetic waves?

    • 0MoTheG
      0MoTheG 28 дней назад

      Where is the contradiction?

  • Eliyahu Kassorla
    Eliyahu Kassorla 1 месяц назад

    It's because cats have pos. Like a cation being positive.

  • Jari Skogster
    Jari Skogster 1 месяц назад

    There is no magnetic force between still standing ions and a moving cat. Still standing charges don't have a magnetic field. You explained a thing that does not exist!

  • frank x
    frank x 1 месяц назад

    BUT electrons in a wire are moving AT A SNAIL'S PACE, (my typing fingers are more time-dilated, relative to the KB than the electrons that shunt a bit when the little connections are made when keys are hit). Care to explain?

  • MidnightSt
    MidnightSt 1 месяц назад

    when i saw the title of this video, i was like "GOD, YES!"
    Awesome. First real explanation of (electro)magnetic fields i ever got. Thank you very much, have an awesome life! :)

  • M Goudsmits 金马桥
    M Goudsmits 金马桥 1 месяц назад

    actually you should be able to test it
    th ecat only needs to do about 30 cm per second

  • lynn rathbun
    lynn rathbun 1 месяц назад

    NO----passing a current through a metal does not make IT a magnet. It makes a magnetic field in space but it does not do anything to the metal.

  • ThunderboltTangerine
    ThunderboltTangerine 1 месяц назад

    Whats the song near the end?

  • Markus Helenius
    Markus Helenius 1 месяц назад

    love ur work

  • DrDress
    DrDress 1 месяц назад

    What!? Is this for real? I've never heard of this. That's amazing!

  • Venkatesh Babu
    Venkatesh Babu 1 месяц назад

    Most of the elements emit some kind of waves because of the properties.

  • IqbalHamid
    IqbalHamid 1 месяц назад

    Who believes this? Yes, it's an interesting idea, BUT it feels contrived. Furthermore, as suggested by the video, the maths don't seem like they would add up. I refer to the speed of the electrons in the wire. Another consequence of this theory which sits uncomfortably with me is that the force on the cat suggests an ASYMETRY between observers. Meaning: in the frame of reference of the stationary observer, there should be no force! He should witness no force! But he does. Hence the feeling of it bring contrived. Is there any experimental or other evidence to support or suggest this theory. Still, it is better than no theory.

  • Alex Botsford
    Alex Botsford 1 месяц назад

    So the faster the cat moves, the greater the magnetic repulsion?

  • Luis Augusto Libório
    Luis Augusto Libório 1 месяц назад


  • Shawn Strickland
    Shawn Strickland 1 месяц назад

    30,330 likes and 330 dislikes, I want to like this but my OCD won't let me

  • Caleb Griffith
    Caleb Griffith 1 месяц назад

    I can't stand Minute Physics narrators voice.

  • Quintin Hansen
    Quintin Hansen 1 месяц назад

    where do the north and south come from

  • Billy Willy
    Billy Willy 1 месяц назад

    Or, like Richard Feynman put it, magnetism is the relativistic aspect of the electric field. But there is really only the electric field. There's also an analogous "magnetic" component of the gravitational field. It's called gravitomagnetism and was measured by the famous Gravity Probe B satellite experiments. Google "Gravitomagnetism".

  • Joaquín Herreros
    Joaquín Herreros 1 месяц назад

    i don't understand the explanation: if a charge is moving linarly in one direction, the electric field and the magnetic field are perpendicular between them and both also with the direction of movent ("right hand law"), so here are saying that the magnetic field is a relativistic efect of an electri field, saying somehow that are only electric fields involved in the right hand law?????

    • 0MoTheG
      0MoTheG 28 дней назад

      The right hand law is based on the conceptual existence of a magnetic field.
      You could formulate a different law that does not need magnetism:
      Equal charges traveling in parallel are repulsed.

  • Alexander Zalesov
    Alexander Zalesov 1 месяц назад

    I'm a bit sceptic about this explanation.

  • Lg Ft
    Lg Ft 1 месяц назад

    I don't wanna talk to no scientist, yall motherfuckers lying and gettin me pissed

    RODLON 1 месяц назад

    Do really electrons drift through wires at 3cm per second?

  • Prasad NSG
    Prasad NSG 1 месяц назад

    You started to clear the fog of magnetism in my brains!!!!!!!!!!!!!!!!!!

  • Jose Lanza
    Jose Lanza 1 месяц назад

    somebody is getting animation graphic designer money

  • RSGTomcat
    RSGTomcat 1 месяц назад

    I've always wondered... if the electrons are moving in your frame of reference (if the cat is also stationary to you) wouldn't they take up less space (and contract) due to special relativity and attract the non moving cat?

  • Jonathan01590
    Jonathan01590 1 месяц назад

    No way you can grow that beard in 6 hours

  • John Coppola
    John Coppola 1 месяц назад

    Albert Einstein said: "The special theory of relativity owes its origins to Maxwell's equations of the electromagnetic field." This viewpoint seems a bit like a circular argument to me. Cool you can explain magnetism this way but the linear Maxwell's equations are a more elegant way to explain it. Can't visualize circular lines of force with the relativity explanation of magnetism really just being moving charges. I think this effect is just a correction term.

  • Nick Flock
    Nick Flock 1 месяц назад

    so wait, when the cat is stationary, is case a:"the fact that the electrons are moving through the wire cause the space between them to contract, therefore attracting the stationary positive cat" true or case B: "The electrons are moving and do shrink but the space is not moving so they stay the same distance apart and therefore do not affect the net charge of the region." Because I could see reason for both. Case A: why else would the electrons move apart as the reference frame begins to equalize speed. no Net difference of movement should show the particles true, unaffected and un-stretched formation and the fact that equalizing speed caused them to spread out leads me to believe that there was contraction when the cat wasn't moving. But case B seems plausible as well because if the electrons were being contracted then one would see attraction between the cat and the wire, yet he clearly stated that there was no attraction between the two.

    1:if one case is correct, then please explain why the other, OR BOTH, is wrong.
    2:if B is correct, then how do electromagnets attract stationary objects?
    3:also, regardless of case, does that mean an electromagnet's strength and even charge depends on how fast you are moving relative to the electrons. For example would the cat traveling half of the electrons speed see more proton contraction and [possibly] less electron contraction cause a weaker force on the cat than if the cat were traveling the speed of the electron, which (in this frame of thinking) cause more proton contraction and [possibly] less electron contraction.

  • Saint Mendez
    Saint Mendez 1 месяц назад

    Dead wrong, magnetism doesn´t work like that. besides, the electrons inside a conductor move about 0.5 mm/s at about 120 v. The magnetic field is produced by alignment of the electrons in a circular motion when being pulled by an electric field opposite to the currents direction. Relativity has no part on it.

  • cody x
    cody x 1 месяц назад

    if we are talking about a non moving cat, wouldn't the electrons be more compressed than when they were still? the non moving cat should be attracted then, right?

    • cody x
      cody x 1 месяц назад

      at 1:31 you say the density would be the same for moving electrons, why does it change for moving protons at 2:01???

  • Jack Specht
    Jack Specht 1 месяц назад

    If this hypothesis were true it would seem that the force of electromagnetism would be calculable in some manner of proportionality to the theoretical time dilation described in special relativity . Since time dilation is described by special relativity as infinitesimally small it would seem that the force origination , generated and described by hypothesis would be negligible even if it were an exponential proportion .

  • Raymond K Petry
    Raymond K Petry 1 месяц назад

    In the static state the positive-cat draws wire-electrons, setting up a mirror wire image of negative charge drawing them together... In flowing, the wire-electrons speed up, nearing the positive-cat, avoiding and repelling it... Were electrons directly, causing, the magnetic field there'd be no current through capacitors—so—current is charge-displacement-flow...

  • Raymond K Petry
    Raymond K Petry 1 месяц назад

    [01:09] "positive metal ions" only if the wire is vapor heated to be an electroplasma...
    [02:00] 'contracted separation' of protons—but—not previously [01:32] of electrons...

  • cole royer
    cole royer 1 месяц назад

    this video brings me back

  • markdude100
    markdude100 1 месяц назад

    There is an error in this video. @2.28 You say that the stationary feels no force; however, in the cat's frame of reference the electrons will appear to be contracted. Therefore, a net negative charge is created, so the cat is then attracted.

  • François Cauneau
    François Cauneau 1 месяц назад

    Wow !! That's teaching !! Congratulations !!

  • Alex Shtyrlin
    Alex Shtyrlin 1 месяц назад

    Shouldn't the magnetic force push the not-moving positive particle only besause of the lenght contraction of the electrons?

  • MindlessTurtle
    MindlessTurtle 1 месяц назад

    that was like watching someone force a square peg in a round hole: you can make it fit, but it doesn't make sense to do that

  • Frank Harr
    Frank Harr 1 месяц назад

    And here I thought cat ions would be negatively charged.

    Oh! And 0.000 000 000 100% c=
    0.00108 km/h,
    0.000300 m/s,
    0.000984 fps,
    0.000671 mph and
    0.000583 kn.

    I can crawl faster than that.

    I guess the force that propels the electrons acts faster than the actual movement of the electrons. That is, electrons push each other away faster than they move. Like a block of wood.

    Also, I gather that the effects of SR have some kind of scaling to do with the nature of the system. So its more noticable, noticible, noticeble, observable in electrons and less so in slowly pitched softballs.

  • Mohammed Benaissa
    Mohammed Benaissa 1 месяц назад

    only in your frame of reference bitch , lol 0:54