Going the speed of light, possibly.

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Discussion Overview

The discussion revolves around the concept of velocity addition, particularly in the context of sound and light. Participants explore whether sound can be perceived to travel faster than its typical speed when emitted from a moving source and whether similar principles apply to objects moving at relativistic speeds, specifically addressing the speed of light.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions the validity of adding the speed of sound to the speed of a moving source, suggesting that sound is not affected by the emitter's speed.
  • Another participant asserts that at relativistic speeds, velocities cannot be simply added due to the principles of special relativity, referencing the velocity addition formula.
  • There is a discussion about the speed of sound being constant in a medium, regardless of the speed of the source, with an example involving a car honking its horn.
  • A participant introduces the idea of firing a bullet from a moving car and discusses how to calculate its speed relative to the ground using the velocity addition formula.

Areas of Agreement / Disagreement

Participants express differing views on the addition of velocities, particularly regarding sound and light. While some agree that sound does not travel faster than its defined speed regardless of the emitter's motion, there is no consensus on the implications for objects approaching the speed of light.

Contextual Notes

The discussion includes assumptions about the nature of sound and light, as well as the application of relativistic physics, which may not be fully resolved. The specifics of the velocity addition formula and its implications for different scenarios are also noted but not conclusively addressed.

DrWafflez Jr.
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I have a question, my bestfriends dad said that if we were driving at 70 mph and then honked the horn, the sound would go 70 mph + the speed of sound. So the obvious question, if that is true can we go the speed of light? But sound is the vibrations of atoms? Does that mean the atoms would have to bump into each other at the speed of light? Last but not least can this be accomplished with a gun being shot or something of the sort? Thanks in advance
 
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DrWafflez Jr. said:
So the obvious question, if that is true can we go the speed of light?

No. At relativistic speeds, you can not add velocities like you usually do, because of special relativity. See Velocity-addition formula (Wiki) and Einstein Velocity Addition (HyperPhysics).
 
Last edited:
Your friend is incorrect, the speed of sound through a medium is not affected by the speed of the emitter.
 
DrWafflez Jr. said:
I have a question, my bestfriends dad said that if we were driving at 70 mph and then honked the horn, the sound would go 70 mph + the speed of sound. ... Last but not least can this be accomplished with a gun being shot or something of the sort? Thanks in advance

Honk the horn and the sound will travel at the speed of sound no matter the speed of the source - sound waves have a particular speed in the air and that's the speed the move at.

Fire a bullet forward from a moving car and the speed of the bullet relative to the ground will be given by the velocity addition formula DennisN mentions (##\frac{u+v}{1+uv/c^2}##) where ##u## is the speed of the car relative to the ground and ##v## is the muzzle velocity of the bullet. For cars and bullets and other slow-moving objects (here "slow-moving" means not tens of thousands of miles a second) this formula reduces to the ##u+v## that common sense tells us to expect.
 

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