Relativity - running person gains mass

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SUMMARY

The discussion centers on the concept of mass increase due to kinetic energy as described by Einstein's mass-energy relation. Participants clarify that while a running person gains kinetic energy, this energy is derived from chemical energy already present in the body, leading to a conversion rather than an actual gain in mass from an external source. The conversation highlights the relativistic effects of mass increase at high speeds, emphasizing that even at 20 kph, the increase in relativistic mass is significant, challenging common perceptions about weight loss through jogging.

PREREQUISITES
  • Understanding of Einstein's mass-energy equivalence (E=mc²)
  • Basic knowledge of kinetic energy and its relationship to motion
  • Familiarity with the concept of relativistic mass
  • Awareness of energy conversion processes in biological systems
NEXT STEPS
  • Research the implications of Einstein's mass-energy relation in modern physics
  • Explore the effects of relativistic speeds on mass and energy
  • Study the conversion of chemical energy to kinetic energy in biological organisms
  • Investigate the practical applications of relativistic mass in high-speed physics experiments
USEFUL FOR

Students of physics, educators teaching relativity, fitness enthusiasts interested in the science of energy and mass, and anyone exploring the principles of motion and energy conversion.

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My physics book tells me: "A person who runs, and thus gains kinetic energy, gains mass (albeit negligible) according to Einstein's mass-energy relation."

I do not think that any energy has been gained from 'outside' the system since the kinetic energy is derived from chemical energy that is already in the body prior to the run. So, how can the body have gained mass?
 
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You're right. The energy was already there, albeit in different form. All that happened was a conversion from one type to another. The point they're making, as I'm sure you're aware, is that there is an inertial equivalent to energy.

Good thinking.
 
And leave us not overlook the immense relativistic mass increase in someone boogying his buns off at 20 kph. So much for jogging to lose weight. :biggrin:
 

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