Experimental evidence for effective mass increasing with speed

[jeremyfiennes]

What is the best recent experimental evidence for effective mass increase (momentum/velocity) with speed, with experimental details? Searching the web all I find is either very old ones (early 1900s). Or vague generalized statements like (Wikipedia) "Many additional experiments concerning the relativistic energy–momentum relation have been conducted, including measurements of the deflection of electrons, all of them confirming special relativity to high precision." Thanks.

 

[weirdoguy]

What is the best recent experimental evidence for effective mass increase

What do you mean by "effective mass"? If what you had in mind was relativistic mass, then this is mostly an outdated concept:

https://www.physicsforums.com/insights/what-is-relativistic-mass-and-why-it-is-not-used-much/

Mass is defined to be lorentz scalar, so it does not depend on speed.

 

[Dale]

What is the best recent experimental evidence for effective mass increase (momentum/velocity) with speed, with experimental details?

There is no need to speak of relativistic mass or "effective mass" here. Momentum divided by velocity is energy in units where c=1. So the best current evidence will be the LHC where protons are routinely accelerated to roughly 7000 times as much energy as their rest energy.

 

[Janus]

Dealing with electrons:

One the early particle accelerators was the Betatron. It used D shaped magnets to curve the path of electrons while they were accelerated at points by charged plates. The electrons would start near the center, and as they accelerated, would make larger and larger circles, spiraling out until they left at much increased speeds.

A factor that made the Betatron such a ingenious device, was that It turned out that, as the electrons sped up, causing them to move out to a greater radius, the increase in speed exactly canceled out the increase distance traveled. The electrons took the same time to make one complete circuit around the accelerator no matter how many circuits they had made and how fast they were going. This meant that the the timing for the charged plates that accelerated the electrons could be a fixed rate for any Betatron.

However, the relativistic momentum increase in the electrons as they sped up relative to the accelerator put a cramp in this. The non-linear increase of momentum with speed, meant that the electrons meant that the paths the electrons followed no longer held to that one to one ratio between speed and path radius. the faster the electrons were accelerated the more they became out of sync with the timing of the pulses sent to the charged plates.

This set an upper limit as to what electron speed could be reached with a Betatron before the fastest electrons got too out of sync with the accelerating plates.

Betatrons were replaced with Synchrotrons, which were designed to change the timing of the accelerating plates to compensate for this effect.

 

[Vanadium 50]

https://www.physicsforums.com/threads/faq-experimental-basis-of-special-relativity.229034/

 

[jeremyfiennes]

Ok. Thanks. All the ones I tried were behind paywalls. Are there any that aren't? Electron/proton e/m measurents.

 

[Nugatory]

What is the best recent experimental evidence for effective mass increase (momentum/velocity) with speed, with experimental details? Searching the web all I find is either very old ones (early 1900s). Or vague generalized statements like (Wikipedia) "Many additional experiments concerning the relativistic energy–momentum relation have been conducted, including measurements of the deflection of electrons, all of them confirming special relativity to high precision." Thanks.

Perhaps the most convincing evidence is that colliders like the LHC work - routinely, every day, with billions of particles. This is not reported in the literature as "evidence for effective mass increase" because it is so routine, just as no one is publishing papers confirming that dropped bricks will fall even though fresh evidence in support of that proposition is being generated at construction sites worldwide every day. (A deviation from the relativistic predictions would be as noteworthy as a levitating brick and would be published... but such things aren't happening, and the fact that they aren't happening is not especially noteworthy).

Thus you'd only expect to find experimental details in descriptions of experiments to find whether the predicted effect happens, and these will of course date back to when this was not yet an established fact.

However, there's another place you could look: electron deflection is a fairly common advanced undergraduate physics lab exercise used to familiarize students with experimental procedures and to see if they're competent to set up and manage lab experiments. This was one of my undergraduate labs almost fifty years ago and apparently it's still being done - A quick google search found http://www.hep.fsu.edu/~wahl/phy4822/expinfo/relmass/harv_relmass.html and http://web.mit.edu/8.13/www/JLExperiments/JLExp09.pdf and plenty more of the same.

 

[Ibix]

Bertozzi's experiment is on YouTube

Not very modern, but straightforward to understand. He actually does the experiment and analyses the results right in front of you.

 

[jeremyfiennes]

Nugatory: thanks. That was what I had suspected. But I had thought there might be a classic experiment that confirmed it once and for all time.
Ibix: thanks you too. The Bertozzi experiment gave me just what I wnated.

 

[jeremyfiennes]

I should also have commented: an excellently devised and presented video. If all scientists were as clear and direct about their experiments as he, there would hardly be a need for Physics Forums!

 

[robphy]

@jeremyfiennes
Here are some other relativity-related videos that you might appreciate.

• Time Dilation : An Experiment With Mu-Mesons (Frisch and Smith, 1962)
  
  
• Frames of Reference (by Ivey and Hume, 1960)
  
  
• Not quite relativity but...
  Universal Gravitation (by Ivey and Hume, 1960)
  
• Einstein's Universe (Calder, 1979) ... this is the video that got me interested in relativity
  

 

[jeremyfiennes]

Thanks.

 

[Mister T]

What is the best recent experimental evidence for effective mass increase (momentum/velocity) with speed, with experimental details? Searching the web all I find is either very old ones (early 1900s).

That's because researchers stopped referring to it as an increase in mass many decades ago. In more recent decades introductory college-level textbooks have followed suit.

What's actually happening is, due to the geometry of spacetime, the amount of energy it takes to speed up a particle increases beyond all bounds (approaches infinity, as they say) as the particle's speed approaches $c$. This is a fact of life, proven every day at places all over the world.

Here's a graph of the data you asked for, taken from
https://courses.lumenlearning.com/physics/chapter/28-6-relativistic-energy/

 

[jeremyfiennes]

Thanks.

 

[Stavros Kiri]

All interesting sources etc. ... Thanks on my behalf too (and thanks to the OP too for the question, disussion etc.).

 

[Meir Achuz]

"One the early particle accelerators was the Betatron. It used D shaped magnets to curve the path of electrons while they were accelerated at points by charged plates."
That is the cyclotron.