Is the outcome of a collision determined by the observer's perspective?

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Discussion Overview

The discussion revolves around the question of whether the outcome of a collision is determined by the observer's perspective, exploring concepts related to reference frames in classical mechanics. Participants examine how different observers perceive the velocities and resulting motions of colliding objects.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that different observers (OA, OB, OC) perceive the collision differently based on their reference frames, leading to varying interpretations of the event's outcome.
  • Others argue that while the speed and direction of objects depend on the observer, this does not have physical consequences, as measurements can be transformed between frames without affecting the collision's nature.
  • One participant suggests that the strength of the impact is related to the velocity difference between the two objects before impact, which remains consistent across different inertial frames.
  • There is a suggestion that the scenario of two cars colliding at different speeds (one stationary vs. both moving) may yield different results, but this is contested by others who emphasize the relativity of motion.

Areas of Agreement / Disagreement

Participants generally disagree on whether one observer's perspective can be considered "correct." While some emphasize the relativity of motion and the equivalence of reference frames, others question the implications of different perceived outcomes.

Contextual Notes

The discussion highlights the limitations of understanding collisions solely from a single reference frame and the need for careful consideration of velocity differences and their implications in various inertial frames.

Flexo
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Consider two objects, a and b, traveling toward each other at, say, 100 m/s.
There are three observers, OA, OB, and OC. With respect to OA, a is stationary. With respect to OB, b is stationary. From OC's point of view, both objects are approaching each other at 50 m/s.
From OA's perspective, b collides with a at 100 m/s. From OB's perspective, the opposite occurs. From OC's perspective, both objects collide at 50 m/s each.

It seems to me that the result of each of these scenarios would be different. OA would see a go backwards, OB would see b do so, and OC would see both cease motion.
Only one of these events would actually occur.
Does that not imply that one of the observers had a "correct" viewpoint?

Additionally, it seems to me that a collision between two cars traveling at 50 m/s toward each other will have different results than one car traveling toward a stationary one at 100 m/s. Is that correct?
 
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Flexo said:
It seems to me that the result of each of these scenarios would be different. OA would see a go backwards, OB would see b do so, and OC would see both cease motion.
Only one of these events would actually occur.
Does that not imply that one of the observers had a "correct" viewpoint?
No. The speed and direction that something moves clearly depends on who is doing the observing. But it has no physical consequence--you can easily transform measurements from one frame to another. (This is the principle of relativity in classical mechanics.)
Additionally, it seems to me that a collision between two cars traveling at 50 m/s toward each other will have different results than one car traveling toward a stationary one at 100 m/s. Is that correct?
No. Let's keep it simple. Say the two cars are sliding towards each other on a frictionless surface (ice, for example) so that no other forces are involved. Whether one car is at rest and the other is moving at 100 m/s, or both move at 50 m/s is simply a matter of reference frame. Pick the reference frame that is most useful--but any will do.
 
Doc Al said:
No. The speed and direction that something moves clearly depends on who is doing the observing. But it has no physical consequence--you can easily transform measurements from one frame to another. (This is the principle of relativity in classical mechanics.)

No. Let's keep it simple. Say the two cars are sliding towards each other on a frictionless surface (ice, for example) so that no other forces are involved. Whether one car is at rest and the other is moving at 100 m/s, or both move at 50 m/s is simply a matter of reference frame. Pick the reference frame that is most useful--but any will do.

I suppose I'm just visualizing it poorly. Thanks, though.
 
Flexo:
The strength of the impact is directly related to the velocity DIFFERENCE of the two objects directly before impact.

Thus, in two distinct inertial frames, although they assign different velocities to the two object, they'll calculate the same velocity difference, yielding the same prediction as to what happens in the collision.
 

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