Velocity Addition Formula: u_y > c?

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SUMMARY

The discussion centers on the application of the velocity addition formula in special relativity, specifically addressing the scenario where a frame S' moves with velocity v = 0.5c relative to frame S. When using the formula u_y = u_y'/(gamma * [1+v u_x' / c^2]), the calculated value of u_y = 1.417c is derived from inputs u_x' = -0.9c and u_y' = 0.9c. However, this result is deemed impossible as it violates the fundamental principle that the sum of the squares of the velocities must be less than c^2, indicating a miscalculation or incorrect assumptions in the initial conditions.

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  • Understanding of special relativity concepts, particularly the velocity addition formula.
  • Familiarity with Lorentz transformations and the concept of gamma (γ).
  • Knowledge of the speed of light as a universal constant (c).
  • Basic algebra skills for manipulating equations involving velocities.
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  • Study the derivation and implications of the Lorentz transformation equations.
  • Learn about the gamma factor in special relativity and its applications.
  • Explore scenarios where velocity addition leads to paradoxes in relativistic physics.
  • Investigate the limits of classical mechanics versus relativistic mechanics.
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Physics students, educators, and anyone interested in understanding the principles of special relativity and the implications of velocity addition in high-speed scenarios.

D O
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If a frame S' moves with velocity v in x direction wrt S, and you have v = 0.5c, u_x' = -0.9c and u_y' = 0.9c then it seems you find that u_y = 1.417c, greater than c.

The relevant formula is:

u_y = u_y'/(gamma * [1+v u_x' / c^2])

Apologies for formatting.

Details: gamma = 1/sqrt(1-v^2/c^2) = 2/sqrt(3)
 
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##u_{x'} = -0.9c## and ##u_{y'} = 0.9c## is impossible because ##u_{x'}^2 + u_{y'}^2 < c^2##.

You can learn how to format equations for this forum here. It's not difficult.
 
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DrGreg said:
##u_{x'} = -0.9c## and ##u_{y'} = 0.9c## is impossible because ##u_{x'}^2 + u_{y'}^2 < c^2##.

You can learn how to format equations for this forum here. It's not difficult.
Oh, of course! Thanks
 

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