Frames of Reference on Top of a Moving Train

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Discussion Overview

The discussion revolves around the concept of frames of reference as it pertains to an object thrown from a moving train. Participants explore the implications of inertial and non-inertial frames, particularly in relation to the motion of the train and the object being thrown, considering factors such as acceleration and relative distances.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants propose that if the train is moving at a constant velocity, it represents an inertial frame of reference, allowing the principles of relativity to apply.
  • Others argue that if the train were accelerating relative to the Earth, it would be considered a non-inertial frame.
  • A participant notes that while the train's velocity is constant, it follows the curvature of the Earth, suggesting that this implies a form of acceleration due to the change in direction.
  • One participant challenges the idea that an object thrown from the train would travel the same relative distance as one thrown from a stationary position, questioning how the distances would compare given the different frames of reference.

Areas of Agreement / Disagreement

Participants express differing views on whether the train's motion constitutes an inertial or non-inertial frame, and there is no consensus on the implications of the curvature of the Earth on the train's motion. The discussion remains unresolved regarding the relative distances the object would travel based on the frame of reference.

Contextual Notes

There are limitations in the discussion regarding the definitions of inertial and non-inertial frames, as well as the assumptions about the effects of acceleration and curvature on the motion of the train and the thrown object.

ZachBirnski
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When an object is thrown by someone standing on top of a moving train, which variations of "frames of reference" would apply? (i.e. inertial, non-inertial, etc.) How would this principle work? (The object would go the same relative distance as it would if thrown from a person standing on motionless ground, disregarding air resistance of course)
 
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You'll have to clarify the question. If the train is accelerating relative to the Earth, it is a non-inertial frame.
 
Brian_C said:
You'll have to clarify the question. If the train is accelerating relative to the Earth, it is a non-inertial frame.

The train isn't accelerating; its velocity is constant. More focus is placed on the action of the object being thrown forward in respects to the moving train than the motion of the train.
 
It is inertial motion and the principle of relativity applies: you can play "catch" in the cabin of a moving train exactly the same if it is moving or not.
 
russ_watters said:
in the cabin of a moving train

Or on top of the train, provided of course that you're not going fast enough to make the wind a factor.
 
ZachBirnski said:
The train isn't accelerating; its velocity is constant.
I never thought of this before, but this particular comment snagged my attention. To some extent, the train is, in fact, accelerating. It is following the curvature of the Earth, which means that its path is actually circular rather than linear. I might be misunderstanding some official terminology, but that constant 'downward' change of vector implies to me an acceleration.
 
ZachBirnski said:
The object would go the same relative distance as it would if thrown from a person standing on motionless ground, disregarding air resistance of course

Assume a person on the platform uses energy E to throw a ball in the direction the train is heading and the ball lands on the ground 100 feet in front of him.
Suppose again that a person standing on the train throws a ball in the same direction, using the same amount of energy to do so. Relative to the person on the train, the ball falls to the ground far closer than 100 feet.
In light of this, how can the object "go the same relative distance..."?
 

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