Does Relativistic Mass Increase with Speed?

  • Context: Undergrad 
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Discussion Overview

The discussion revolves around the relationship between energy expenditure and speed during physical activities, specifically comparing running and walking, as well as the implications of the equation E=mc² in these contexts. Participants explore both theoretical and practical aspects of energy consumption in motion, including the effects of speed on energy requirements and the role of drag and friction.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant argues that energy burned while running a mile is greater than while walking due to increased velocity and energy conversion, while another counters that E=mc² is not relevant to this scenario.
  • Participants discuss the kinetic energy formula Ek=0.5mv², suggesting that higher speeds lead to greater energy expenditure, but disagree on the applicability of E=mc² in everyday motion.
  • There is a mention of drag and wind resistance, which increases with the square of velocity, impacting energy requirements for faster movement.
  • Some participants express confusion about the meaning and application of E=mc², with one suggesting it applies to all motion, while others clarify that it primarily relates to mass-energy conversion in nuclear reactions.
  • One participant asserts that the effects of E=mc² become significant only at speeds approaching the speed of light, implying that for typical running or driving speeds, its impact is negligible.

Areas of Agreement / Disagreement

Participants generally agree that energy expenditure differs between running and walking, but there is significant disagreement regarding the relevance and application of E=mc² in these scenarios. Some believe it applies broadly, while others argue it is limited to specific contexts like nuclear reactions.

Contextual Notes

Participants express uncertainty about the implications of E=mc² and its relationship to energy expenditure at everyday speeds. There are also unresolved questions about the definitions and assumptions underlying the discussion of energy in motion.

Who May Find This Useful

This discussion may be of interest to those exploring the physics of motion, energy expenditure in physical activities, and the implications of relativistic physics in everyday scenarios.

  • #31
First off regarding the comment
E=mc2 where m is relativistic mass represents the Total Internal Energy of any mass m,..
This isn't quite right. The internal energy is the energy inherent to the particle itself - i.e. E_o = m_o*c^2 = rest energy.

Note: The quantity gamma*m_o*c^2 is not the total energy of a moving particle of proper mass m_o. It's the kinetic energy plus the rest energy. The total energy is the kinetic + rest + potential.

See --- www.geocities.com/physics_world/relativistic_energy.htm

Regarding the comment
Can one still get away with talking about relativistic mass?
I thought the current generation of physics custodians give one the back of the handle for saying that.
I hope the answer is YES.
Sure. You can always talk about relativistic mass. Many physicists still do. Even recent GR books do. There are no "custodians" in physics. There is an entire spectrum of ideas and opinions. It just so happens that the con-relativistic mass people are more apt to try to force their ideas on others. The pro-relativistic mass people know that it's a matter of definition and use it was they see fit.

Don't let them fool you though. Relativistic mass is the closest thing you'll get to the having the all the properties one normaly associates with mass.

Pete
 
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  • #32
Thanks, Pete. I feel better already.
 
  • #33
Originally posted by quartodeciman
Thanks, Pete. I feel better already.

Glad to help. If you'd like I can scan a few articles in and e-mail them to you. One is a response by Wolfgang Rindler (a well known relativist) who wrote and article for Physics today defending relativistic mass. There is another one from the American Journal of Physics called "In defense of relativistic mass" that you might enjoy.

Just e-mail me at peter.brown46@verizon.net

I can also send you the paper I'm writing on this very concept. It's in a good enough stage that I don't mind letting someone read it at this point.

Pete
 

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