tag:blogger.com,1999:blog-3993498847203183398.post8436261483782602329..comments2024-08-07T12:56:22.512+01:00Comments on RevK<sup>®</sup>'s ramblings: E=mc²RevKhttp://www.blogger.com/profile/12369263214193333422noreply@blogger.comBlogger12125tag:blogger.com,1999:blog-3993498847203183398.post-52143986184290139762018-09-03T03:11:41.179+01:002018-09-03T03:11:41.179+01:00In advanced physics texts, very often it is chosen...In advanced physics texts, very often it is chosen to let c=1 and define the system of units accordingly with also h=1 or h bar = 1. So then E = m.<br /><br />The reason that it was E=mc² is because that is correct _in the particular system of units in use_, SI units and with a particular definition of ‘total relativistic energy’.Cecil Wardhttps://www.blogger.com/profile/16477035597238561739noreply@blogger.comtag:blogger.com,1999:blog-3993498847203183398.post-18107693584931230512018-08-28T19:40:28.966+01:002018-08-28T19:40:28.966+01:00https://www.amazon.co.uk/Why-Does-mc2-Should-Care/...https://www.amazon.co.uk/Why-Does-mc2-Should-Care/dp/0306819112<br /><br />is a good read and explains it all.Anonymoushttps://www.blogger.com/profile/02860896205551634066noreply@blogger.comtag:blogger.com,1999:blog-3993498847203183398.post-24589431487144302872018-08-28T19:39:23.150+01:002018-08-28T19:39:23.150+01:00https://www.amazon.co.uk/Why-Does-mc2-Should-Care/...https://www.amazon.co.uk/Why-Does-mc2-Should-Care/dp/0306819112<br /><br />is a good read and explains it all.Anonymoushttps://www.blogger.com/profile/02860896205551634066noreply@blogger.comtag:blogger.com,1999:blog-3993498847203183398.post-30165891174011340692018-08-28T13:10:21.329+01:002018-08-28T13:10:21.329+01:00ke = ½mv².
So the actual hypothetical (non-relati...ke = ½mv².<br /><br />So the actual hypothetical (non-relativistic) speed would be sqrt(2) times c.<br /><br />I used to be able to derive E=mc² from first principles, but I've forgotten the details. Fortunately we have Wikipedia.<br /><br />https://en.wikipedia.org/wiki/Mass%E2%80%93energy_equivalence#The_first_derivation_by_Einstein_(1905)RogerBWhttps://blog.firedrake.org/noreply@blogger.comtag:blogger.com,1999:blog-3993498847203183398.post-23665183407269996702018-08-28T10:25:38.115+01:002018-08-28T10:25:38.115+01:00The key to understanding this is Dimensional Analy...The key to understanding this is Dimensional Analysis. This is where we break down quantities into their base units. All quantities can be expressed as combinations of the four elements, Length (L), Mass (M), Time (T), and Electric Charge (C). So the speed of light has dimensions L/T Length divided by time. <br /><br />The kinetic energy of a body is the its Mass x Velocity. So the formula says that the energy of matter is equivalent to its kinetic energy if it were traveling at the speed of light squared.Stuart Wardhttps://www.blogger.com/profile/11152511520405147616noreply@blogger.comtag:blogger.com,1999:blog-3993498847203183398.post-14665446406645004322018-08-26T18:02:58.141+01:002018-08-26T18:02:58.141+01:00the e stands for eggsthe e stands for eggsAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-3993498847203183398.post-46206624930659902302018-08-25T19:50:51.993+01:002018-08-25T19:50:51.993+01:00As others have said, you can use any units you wan...As others have said, you can use any units you want as long as you're consistent in your derivation of energy (ie that unit is not "totlly arbitrary"; it comes from the others).<br /><br />It's like saying "In the UK we count using ten digits and my keyboard just happens to have them all on there. If we used something other than ten digits then the keyboard would have to be different, yet it isn't. I find that a bit convenient."<br /><br />PBC Space Time's vid on the origin and meaning of this equation is interesting.<br /><br />https://www.youtube.com/watch?v=Xo232kyTsO0<br />chrislnoreply@blogger.comtag:blogger.com,1999:blog-3993498847203183398.post-39050341975413543872018-08-25T16:02:07.595+01:002018-08-25T16:02:07.595+01:00It would still be C squared, in whatever units you...It would still be C squared, in whatever units you were using. But the measurement of energy would then be in KgFeet2/minute 2 instead.Andrew Duckerhttps://www.blogger.com/profile/06566110014858668221noreply@blogger.comtag:blogger.com,1999:blog-3993498847203183398.post-40970498573160027042018-08-25T15:42:05.092+01:002018-08-25T15:42:05.092+01:00So, my first comment has not shown up. I'm hop...So, my first comment has not shown up. I'm hopeing that was because Adrian didn't see it rather than he censored it.<br /><br />Joules is a derived unit so any change in the definition of the metre, second or kilogramme will change the size of a Joule.nowtotallyhackedoffhttps://www.blogger.com/profile/06687184924812362495noreply@blogger.comtag:blogger.com,1999:blog-3993498847203183398.post-50616382145506998252018-08-25T15:06:12.339+01:002018-08-25T15:06:12.339+01:00That’s an interesting question. I think there’s a ...That’s an interesting question. I think there’s a clue when you said that MOST of the units are totally arbitrary. The SI system is what’s called a “coherent” system of units, which means that the units are defined in relation to each other according to the physical laws and with no multiplication factors (so 1 joule of energy is defined as 1 kg m^2 s^-2). And one of the the advantages of doing things that way is that it simplifies the equations, so we can say that e = mc^2 in any coherent system of units. In an incoherent system of units there would be a conversion factor, as you say.JJC1138https://www.blogger.com/profile/03178758568612019553noreply@blogger.comtag:blogger.com,1999:blog-3993498847203183398.post-18357886746327805102018-08-25T14:01:27.172+01:002018-08-25T14:01:27.172+01:00Physicists often treat standard constants as 1, as...Physicists often treat standard constants as 1, as they are tied to our real-world measurement units for real-world use but can be anything in the abstract. So in their case E = m, and they often don't even bother with m - it's all energy anyway.<br />John Sagernoreply@blogger.comtag:blogger.com,1999:blog-3993498847203183398.post-41440713818013399382018-08-25T08:23:13.757+01:002018-08-25T08:23:13.757+01:00Not sure I understand why any of those are more co...Not sure I understand why any of those are more convenient than any of the others, but as far as the units are concerned, while arbitrary they are also very much linked:<br /><br />https://www.reddit.com/r/funny/comments/2e2do9/_/cjvgh34Matthewhttps://www.blogger.com/profile/04311149395810537121noreply@blogger.com