Relativistic Addition of Velocity | Special Relativity Ch. 6
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- Опубліковано 11 чер 2018
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Mark Rober's youtube channel: / markrober
This video is chapter 6 in my series on special relativity, and it covers the topic of relativistic addition of velocity: aka, how things that are moving relative to one inertial reference frame, which is moving relative to another reference frame, what speed or velocity are those things moving relative to the second frame. We'll show this using the Lorentz transformation of moving worldlines, enacted with a mechanical minkowski diagram, aka mechanical Lorentz transformation, aka spacetime globe.
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Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute!
Created by Henry Reich - Наука та технологія
Avoiding demonetization by calling it a death pellet. Nicely done.
Cody'sLab that was exactly my thought
It only show how fucked up the entire system is, if we must use synonyms for normal objects in order to avoid the system penalty.
PotatoSmasher 1984 comes to mind
Ministry of Hatespeech is apparently a thing in youtube.
first time I understood the speed of light can't be surpassed.
I have to say, a bullet traveling at 0.6C definitely earns the name “death pellet”.
ANYTHING at 0.6C deserves.
@Pedro Nunes
Not so sure about that part. I am getting hit by plenty of things going upwards of 0.99C. Heck, my comment is hitting you faster than 0.6C right now.
Even a speck of paint counts as one. Remember Mass Effect lore?
Pedro Nunes not really neutrinos for instance travel faster then that and aren't dangerous at all even in high quantities
Ok, anything that is in a human scale.
I'll say it again. This spacetime globe is a work of genius. Hand this man his nobel prize.
* this man => Mark Rober FYI
This active visual presentation finally made it click for me. Brilliant.
Yeah, I really want to buy one, it doesn't look like he ever out them up for sale. 🙁
@Donald Deng my guess is MinutePhysics did a sketch of what these Lorentz Transformation diagrams look like and sent it to Mark, and Mark probably came up with some ideas of how it would look physically and then they both kind of agreed on what looked best and then Mark built it. I think it was the two of them working together to create this.
Naming a planar Device a globe is not that genius at all! haha ;)
I spilled water all over my keyboard.
"Death pellet"
Demonetization bot hitting hard on everyone's vocabulary.
Quahntasy - Animating Universe is avoiding demonetization that easy? And that crucial?
Think about it, you live from the revenue of ads. You get demonetized and lose your income. What should you do for a living? Quit the job and make something different? No. Change your work on some parts so you wont lose your income? Yes.
Demenetization comes from stupid bots and stupid people, so you can atleast hower away from the bots with some cleverness.
The video it's sponsored so it doesn't matter
just say "if you throw a ball"
Let me just take away half your paycheck, because as long as you don't have the other half it doesn't matter.
100 quadrillion neutrinos walk into a bar. One of them says ow
not a lot of people will get this
May you describe it for the people that actually don't get it ?
Help, lol
AH HA HA HAAAAA! 😂
Hahaha. It's funny because, being neutral in charge, neutrinos have notoriously low detection rates. Thus, even though 100 quadrillion neutrinos experienced the effect of "walking into the bar," only one alerted nearby observers.
That is fascinating. So now I know that all my physics assignments where I added speeds were wrong after the 13th digit behind the dot.
Not My Name
Unless the input values were improbably precise, your answers were correct to the number of significant figures given.
Death pellets do not travel faster than the speed of light, but love pellets do because they cause your universe to enlarge.
Also, love can go thru multiple dimensions. This is, of course, according to Interstellar.
Yo somebody else using a zombatar ayeeeee
Classiest boner joke ever
And then there's friendliness pellets that boost your LOVE...try to catch as many as you can lol
So cheesey that it's good
The first few minutes of this video taught me what years and years of physics courses couldn't.
for any high schoolers / college students taking the class: this is the formula for success
1) watch this video
2) read it in detail on brilliant.org
3) read it in mathematically rigorous detail of physics.libretexts
4) watch it on khan academy for review
Done. You're a master at it now. It comes intuitively after doing this cycle.
lol i'm a kid i tried for 2 years to learn that, i don't know why i didn't get this series :(
*I lost him at "In our universe".*
Shaolin Panda it’s a joke bruv
Alex Ryan Hughes He is saying that because there is a possibility that there are other universes where apply different laws of physics
@Chính Đặng Minh kudos to u.......
I love the way you animate your algebra. It captures really well the actual visualizations of someone who's doing the math.
I love that u repeatedly recap over and over the example in the beggining of each video in this series, it really helps me to fix the idea instead of remembering for myself the main idea that u already explained in the previous video
you really expand my coceptual understanding of the topic.
people say classical physics and relativity don't match up but the truth is when we talk about things moving at the speed of light we get to discover what really happens on the small scale..
At least they're not "friendliness pellets."
Thank you for this. Due to corona making all my classes online. My class on special relativity and related subjects has been entirely just "read the book" kinda stuff. Really love the fact that there are explainations like this that help provide intuition for topics like lorentz transformations, lorentz invariance, and relativistic addition of velocity.
Can you please tell which for which fields you'll learn special relativity in college other than Physicist?
@@tahamuhammad1814 there's quite a few. Off the top of my head, Anything that usually requires precision in timing or travels at high speed. So, like, communications engineering (satellite communications, telecom, signals, etc). Even things that move at high speeds, think NASA travel, will require compensation. Rocket science probably as well. But in general, if you can think of a field where precision at high speed is required, there's probably some special relativity being applied.
A few years ago I took an online course through Stanford concerning the Special Theory. It was a superb course, and it required "homework" and tests so that the student must understand the material before proceeding.
I had a pretty thorough understanding of the concepts, but the addition of the spacetime globe in this series brought everything together. Using that instead of drawings was much more clear. Thank you so much!
That part about stretching the drawing made me understand the whole thing. And in the end you completed it by explaining how the Math works out for it. This is a great video
is he saying death pellet instead of bullet cause demonetization?
Dynamitris the Video Watcher yes
Dynamitris the Video Watcher well but also a bullet at .6c is a death pellet.
Technically the term is "kill vehicle," but sure, 'death pellet' works too.
Annihilation pebble*
@@yzmotoxer807 Oblitaration projectile.
I can understand that guy when I listen to him at 0,75x speed
This series has done more for my understanding of relativity than all of my high school physics classes. Keep up the great work, and thanks so much for the time and effort you put into making these!
I think this is one of your best videos! congrats for making this so simple
"Death pellet", gotta keep the demonetisation bots away
a death pellet a day
keeps demonetization away
Oh wait, UA-cam actually demonetize videos for using the word "bullet" or? :O
Gets demonetized anyways for saying death too many times
Always Watch at 0.5x speed if you're a Noob.
Vivek Joshi Sounds extremely high at that speed
x0.75 sounds way better
*0.75x speed
i'm a advance noob :v
I watch it at the speed of light.
yeah ikr it really helps
this is my favourite video on all of youtube! It answered a question that I had FOR A LONG TIME
I'm really digging this series on special relativity. Thanks for making it!
Incredible.
friendly pellets
*flowey is that you?*
i'm just a friendly neighborhood flower.Nothin' more :)
I laughed twice when I remebered he calls them bullets if you dodge them.
I love these videos.... and almost all of them go over my head. But i am starting to understand now, so thank you!
these explanations are so good, I'm loving them keep up the good work!
death pallet xD god damit youtube look at what we have to do to bypass yar crap
the shit PC world we are living
Death pellets don't kill people. People kill people.
You'd think the NRA would *love* to advertise on videos about guns, so why does youtube demonetize them?
be cause having your ads on high quality educational videos will trash your reputation.
DUH
Drinking game.
Every time “the speed of light” is said, you have to drink
Wow.... Now I understand the whole stuff.. thank you minutephysics. I've been following this series from the first episode and you have taught me a lot. Thank you once again.
It's becoming more and more clear with each video .. thank you so much
You are the best!
what about two photons travelling in opposite directions towards each other? I still can't grasp that one
It's a tough question to answer without more information. Do you mean from the Photon's perspective? Or a different observer?
well from one of the photon's perspective would be the worst (or rather weirdest) scenario
From the perspective of anything traveling at the speed of light, time does not pass. It's an interesting property of our universe that the speed of light happens to be the fastest that any two points in space can communicate with one another. Photons happen to carry that information.
Imagine this: A photon from a distant star is emitted. That ray of light travels from lets say 100 thousand years before striking your eye, and turning into an electrical signal. During that time, the photon has traveled through an enormous amount of space. Yet, when it strikes our eye, we do not see any other information. We only see the point of origin of that photon. It has carried information about that star across vast distances, unchanging, to your eye.
The reason cause and effect are consistent for all observers is that the universe has a speed limit.
If you look at the path of a photon on that space-time globe, it is *always* at 45 degrees to the current perspective. Ergo, "From the photon's perspective" itself doesn't make sense, because you can never have the photon's world line going straight up. If you did, everything else would be moving at infinite speed. Not light speed, literally infinite. rendering time non-existent.
well that last one just blew my mind back to the start, I was interpreting that from the point of view of one photon, time does not pass and the rest of the universe stands still, therefore from its point of view other photons would be still, therefore relative speed would still be C, but hidden ninja practically scrapped that idea, if time does not pass, and speed is a function of distance over time, how does a photon even move? however I would assume there has to be a point of view for the photon somehow valid.
as for the 3rd observer, I'm guessing the formula balances out in the middle somehow? though I'm still not sure how
You've just been knocking it out of the park lately, Henry
I really really really like these videos. You helped me visualize relativity in a way I was struggling to for years!
That is a simple equation. I didn't think that equation that would allow for slow speeds to add but disallow super-luminal speeds would be simple.
That's the beauty of physics.
Yep, very similar to the equations for time dilation and length contraction using the Lorentz factor!
can you manufacture the device so that everyone can buy it
Yeah, tell Mark to make me one too. I wonder how much he'd charge.
It looks like a pretty easy build if you have access to a minor machine shop.
Definitely an amazing series. Congrats!
That was a great video! I have always wondered about that; so thank you for finally making it clear to me... 👍
Now I understand why good professors take a pause when they explain something before throwing something new at us, it's so we can take our time to think about the info at hand and give us time to prepare for the next one.
Here you do all this amazing job preparing the videos but you go too fast throwing new information left and right. After a while pausing, going back, slowing the video etc.. starts to be a pain.
zouhairy yes but you can go back
zouhairy
Thank goodness you can pause and skip back when watching a video on your own. (However, you are right that it makes the video more difficult to use in, say, a classroom setting.)
zouhairy It's called minutephysics for a reason. I appreciate the speed because I often find other videos way too slow. This one was perfect for me, but if I don't understand, I can just go back until I do, or look up a more detailed exlpanation if I'm really stuck.
zouhairy He is, this video was a singular concept, building on information from his previous videos.
The start of the video recapped on what has already been taught, then the new equation was introduced with an explanation.
Any less content and there wouldn't be any content, any longer of a video and it'd be repetition.
There are sections where he's wanting you to think for yourself, such as considering the equation at the lower values of c, but what good professor wouldn't want you to think for yourself at least a little?
You can control the speed of any video on YT. I usually watch these videos at x1.5 so I can’t really see the problem... and being not too repetitive is one of the things I love from this channel.
I would like to know what would be the relative speed of a light coming from the opposite direction if I am already move at the speed of light? Just like the LHC crashing two particle at opposite direction, is it the same with just one particle crash at the speed of light into a stationary one?
cfsscfsshk Both particles would move at a speed close to that of light. Viewed from the perspective of one particle, the other particle would move at almost the speed of light towards them.
cfsscfsshk You can't move at the speed of light because you're not a photon (and you have mass). If you were a photon, the question wouldn't make sense because you wouldn't experience the passage of time, and thus "speed" is meaningless.
+Buttercak3
There you go.
So basically still the speed of light.
+David Guild
Oh wow. Pretty smart stuff
Now that I'm at a proper keyboard rather than a phone, I can actually type a bit more about this. Note that it's been a while since I went to school and learned about this topic, so don't take anything I say as facts and consider doing some more research.
Particles that have mass can move at a speed close to that of light, but not *at* the speed of light. You can perform Lorenz transformations for the perspectives of two particles that move towards each other with such speeds and will see that the other particle's speed will appear a bit closer to the speed of light than before.
If we're talking about two particles that *actually* move at the speed of light towards each other, like two photons, things get a little weird. You probably noticed throughout these videos that you can't really perform a transformation that creates the perspective of a photon with the time globe. What you can do, however, is plug the speed of light into the transformation formulas from last video as v.
I'll have to do some workarounds to be able to express the formula in a comment. "dx" and "dt" stand for "delta x" and "delta t", "sqrt" for the square root of what's in the parentheses.
Length contraction: dx' = sqrt(1 - v²/c²) * dx
If v is equal to the speed of light, then v²/c² equals1. The part under the square root evaluates to 1-1, which is equal to 0. The square root of 0 is 0 and you multiply that with delta x to get the result. Basically, you get dx' = 0 * dx, meaning that everything that moves at the speed of light appears with a length of 0.
Time dilation: dt' = dt / sqrt(1 - v²/c²)
If v is equal to the speed of light, then the square root evaluates to 0 again, like with length contraction. Now you're left with dx' = dx / 0. Now here is where I'm not sure, so take this with a grain of salt. Division by 0 is obviously not allowed, but what if you interpret the result of dx / 0 as infinite? Time would be infinitely streched, causing time for things moving at the speed of light to stop.
These two things mean that, viewed from the perspective of a photon, everything has a length of 0 and time of everything around it is slowed to a halt, effectively eliminating the concepts of space and time altogether. What does this mean or look like? I don't know. I'm not a photon.
I love this series and have watched every episode multiple times by now. Still hoping I'll understand it one day...
This video is really cool because it blew my mind. I love it
Those death pellets are quite speedy quick. Better watch out.
I’m curious, do you call it a “death pellet” because saying “bullet” would get you demonitised? :S
This explanation actually cleared most my doubts regarding special relativity. Thank you very much.
This. Is. Just. So. SoOooOo. Sooooo. SOOOOOOO GOOOOOD!!! Thank you Henry!
ummm just pretending that I understood
Questn you will understand it clearly once you question it yourself, and wonder why and how is it
Basically our general understanding of how things move applies the same to things moving waaay faster, but the outcome looks significantly different from our perspective. However, our understanding of the universe is that the speed of light cannot be surpassed by us because that’s just the nature of our universe.
🙃😶😵
How it works is actually pretty simple. Why it works that way took one of the greatest minds in history to figure out.
The theory of Relativity is about how the quantities that are measured by one observer (Alice) relate to corresponding quantities that are measured by another observer (Bob) who are moving with respect to each other. The value of some quantities change depending on your perspective; such as the velocity of an object, the time interval/the distance that is measured between a pair of events, the energy/momentum associated with a physical system, etc. Transformation laws describe how the values change from the perspective of one observer (Alice) to another (Bob) depending on how the first observer (Alice) is moving with respect to the second (Bob). The equation involving the velocity of an object with respect to one observer (Alice) and the velocity of that observer (Alice) with respect to a second observer (Bob) is just another example of a transformation law that allows the velocity of the object with respect to the second observer (Bob) to be computed. So in this case, it's a transformation law for the velocity of an object. There is a transformation law for every quantity that is relative (i.e changes depending on your perspective).
These transformation laws can be deduced from two experimentally verifiable starting points:
a) The laws of physics have the same mathematical form in all inertial frames of reference.
b) The speed of light in a vacuum is measured to be the same by all observers.
The laws of physics describes the patterns among the quantities that can be measured by any observer in a particular frame of reference. Transformation laws describe how those quantities change from the perspectives of observers in different frames of reference.
Wait what?
That was awesome, fun to watch.
These videos are quite mindblowing, love it!
gg laws of physics
well played
obama approves
Imagine you have a train on the train you have a train on this train you have a train... and so on... Will we reach the speed of light ?
Dagobert Duck no
Dagobert Duck it’s just like 1+half+half of half+half of half of half, you’ll never get to 2
No you wouldn't, however some theories suggest that 'time' would slow down the faster you go. So if you were able to make this 99.999% speed of light train you could, in theory, have a time machine to the future.
Just a time machine to the future though, not the past.
Although you could just sleep more, and it would be more fun in my opinion.
Time slowing down isn't just theoretical, it really does happen. Clocks on GPS satellites have to be so precise that the slight change in the speed of time due to them being farther from Earth's gravity means that they have to adjust their clocks by a tiny fraction of a second each day. Same thing happens on fast planes, precise atomic clocks that start out since but then one fly's around the world in a fast jet the jet clock is slower.
This video really helped me out! I now finally understand it!!
This series is amazing
Hah! Your spece-time globe is *flat!* Thus proving the flat earth!
The only thing flat-earthers have to fear is sphere itself.
And cats traveling at the speed of light firing death pellets.
Hmm, I think it's a flat universe, if one even knows what that means. But, I got the joke.
He explicitly said he is viewing the earth in one dimension
In contrast to the earth, the universe/space-time is in fact flat (at least as far as we can measure).
Flat Earth😂😂😂 some no many believe in flat Earth theory
Isn't the universe expanding faster than light?
it's the "empty space" that is expanding not the matter such as earth and the sun that is moving faster than light so there's no rule broken
Manh Do however, it is said that matter over 14 billion light years away is moving faster than the speed of light relative to us, so at this current technology, nothing can reach it or we can never see anything beyond it.
our observable univer have the diameter of 90 billion light year
Manh Do
19*
Manh Do makes more sense, i think I mistook for the big bang or something, so my bad. But I'm glad I said over 14 billion, haha
This is the best video I've seen on this topic.
3:16 Such a simple yet elegant equation. As you started writing it, I deduced what it would ending up looking like. It's very intuitive.
I didn't understand it
this video is incorrect!
I clicked the notification bar faster than the speed of light...
Gh0st No, he could’ve stopped. Though, his hand would burn
No you didn’t, you clicked it at the slow, slow speed of your finger touching your phone. It would require an infinite amount of energy to move mass through space at the speed of light, so beyond that is even more impossible.
Even if you had managed to click it that fast, the speed of the components in the system would not have delivered the video to you faster than the speed of light.
*Pretends to understand what's going on...*
I love the time globe series, it really helps one visualize the concepts.
Thanks for the video! Keep up the great work
Why speak so fast? (English is not my first language)
Raul Afonso Because its hus first language. I speak Mexican spanish, poorly, tge mexican speak so fast I only catch about every third word. Is what it is.
If you go to settings, you can slow down playback speed to either .75x, or .5x
You are welcome
Raul Afonso its called minute physics for a reason...
disliked for calling bullets death pellets.
Seth Apex UA-cam fault.
weak hyper charge
bullets are not always lethal depending on where they hit, therefore changing the name is inaccurate, though apparently he did it to avoid youtube censorship.
I'm not sure why my dislike is not showing up in the counter, but when i try to remove it, the counter goes to -1 dislikes.
I'd point out any bullet moving at 0.6c very much is going to be a death pellet no matter where it hits you.
So you are aware that he calls bullets like that not because he thinks they should be censored, but to avoid youtube penalty, and despite that you give a dislike? Shouldn't you be mad at youtube instead?
Red Claw I'm mad at both. UA-cam for the censorship, Henry for not calling attention to the censorship.
You guys made a similar videos before, this one adds much more
This brought me to tears. Life is beautiful
I read that equation in a book as a teenager and I still know it by heart. I love it so much; it's so elegant! 😍
Wow! Great way of explaining things like that.
very nice explanation. I like your visual model and examples.
Very nice video. Please continue the series
amazing demonstration!
You sir saved me!!! Now I understand not only the formula (for which I came in the first place) but the concept behind! Thank you sincerely ❤
Very nice explanation. Great job
This is such a great series
Thank you! Best explanation I've seen for why nothing with mass can travel the speed of light or faster.
this space time globe actually made me understand that. tanks dude
Your spacetime globe made me think everything is always moving through 4d spacetime at the speed of light. Either moving at the speed of light through time when stationary, or when moving through 3d space at the speed of light your speed through time is zero. Very cool, it really puts time dilation into much clearer perspective.
I need to go make a spacetime globe now lol! Many thanks for this video set!
any videos that's explain thing with diagram on relativity theory, should uses whatever weapon that is used in this video. really helping. love it...
This was super helpful. Thanks!
I love this series!!!
There is so much new stuff on UA-cam it's overtaking the peer reviewed periodicals.
thank you for making my brain tick again!
One of the greatest channels of all time
As always cool video!
man that was awesome, I always ask myself that question, thanks
Still absolutely loving this series. I never got to relativity in college physics.
I finally understood why (2/3)c+(2/3)c!>c ! Thank you so much minutephysics. All I needed was that equation.
this is the best lorentz transformation diagram ive ever seen
Thank you for the explanation!
3:49 In case anyone's wondering: (v+u)(1+vu/c²)
Thanks for showing and explaining the formula. Anytime someone asks about "turning on a flashlight while at lightspeed", I'll refer them here.
Great video!
Nice explanation!
This video showed a better explanation of relativistic relationships better than the other one using the same graph
Dude, you're a genius, you made this theory so simple to understand that even me could, thank you!
Good content, Henry.
Estos videos están demasiado buenos!
great explanation. thanks