Negative Acceleration: Deceleration or Reversal?

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Discussion Overview

The discussion revolves around the interpretation of negative acceleration in the context of motion, specifically whether it indicates deceleration or acceleration in the opposite direction. Participants explore the implications of acceleration time graphs and their relationship to velocity, addressing both theoretical and practical aspects of motion analysis.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that negative acceleration indicates deceleration when it opposes the direction of velocity until the object comes to rest, after which it accelerates in the opposite direction.
  • Others argue that the acceleration time graph alone cannot determine when an object comes to rest, suggesting that knowledge of the velocity graph is necessary.
  • A participant questions how to identify the point at which an object comes to rest using the acceleration graph.
  • There is a discussion about the implications of a body moving with constant velocity and then stopping instantly, with some suggesting that such a scenario would imply an infinite acceleration at that instant.
  • Another participant clarifies that if a body stops "in an instant," the acceleration would theoretically be negative infinity, but in reality, it would occur over a very short time with a large negative magnitude.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of negative acceleration and its implications for motion. There is no consensus on whether negative acceleration should be classified strictly as deceleration or as acceleration in the opposite direction, and the discussion remains unresolved regarding the specifics of graph interpretation.

Contextual Notes

Limitations include the dependency on the definitions of terms like "deceleration" and "rest," as well as the need for additional information about velocity to fully interpret acceleration graphs.

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in acceleration time graph when the acceleration is constant. Then at an instant it has negative acceleration. Does this mean that the body is decelerating or it is accelerating in the opposite direction. eg. http://hyperphysics.phy-astr.gsu.edu/hbase/mechanics/motgraph.html {last graph}
 
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When an object decelerates it usually means that the acceleration vector points in the opposite direction of the velocity vector. So when you apply a negative acceleration to an object it decelerates until its velocity reaches zero then it begins to accelerate in the direction opposite of the original motion.
 
how can u tell from the graph when the object comes to rest?
 
Phrases such as "comes to rest", "is at rest", and "starts from rest", all refer to the velocity. The answer lies in the velocity graph, because being at rest means that the velocity is equal to _____?
 
i was referring to the acceleration time graph.
 
It cannot be determined from the acceleration graph alone. You would need to know the velocity at some point in time, then it could be determined by taking the integral of the acceleration. (Have you taken a calculus course that covers integrals?)
 
my only problem is with the acceleration time graph. let's say a body is moving with constant velocity. THen in an instant it stops and accelerates in the opposite direction. Then wouldn't the graph be same as the graph mentioned above?
 
Then wouldn't the graph be same as the graph mentioned above?
No, the acceleration graph would be different:
my only problem is with the acceleration time graph. let's say a body is moving with constant velocity.
Okay. What is the acceleration while the body is moving with constant velocity?
THen in an instant it stops and accelerates in the opposite direction.
If it stops "in an instant", the acceleration would be -∞ for that instant. In actually, the body would stop in a very short time (not an really an instant), and the acceleration would have a very large magnitude and be negative.

Hope that helps.
 

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