Why is Acceleration Proportional to Negative Displacement in SHM?

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Discussion Overview

The discussion revolves around the relationship between acceleration and displacement in simple harmonic motion (SHM), specifically why acceleration is proportional to negative displacement. Participants explore the implications of this relationship within the context of SHM and related physical laws.

Discussion Character

  • Conceptual clarification
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant states that in simple harmonic motion, acceleration is defined as -W²x, where W is a constant and x is displacement, questioning the significance of the negative sign.
  • Another participant explains that acceleration and displacement are vectors, indicating that the negative sign reflects the opposite direction of acceleration relative to displacement, acting as a restoring force.
  • A different participant agrees with the previous point, noting that the sinusoidal nature of SHM arises from the derivatives of sine and cosine functions, where the negative sign in acceleration indicates it is opposite to displacement.
  • One participant references Hooke's law (F = -kx) to further illustrate that when displacement is positive, the resulting force and acceleration are negative, emphasizing the importance of the negative sign in this context.
  • Another participant reiterates the question about the negative proportionality of acceleration to displacement, seeking further clarification.
  • One participant suggests that the elasticity of the spring contributes to the negative relationship, as it resists changes in shape.

Areas of Agreement / Disagreement

Participants express varying degrees of understanding regarding the negative relationship between acceleration and displacement, with some providing explanations while others continue to seek clarification. There is no consensus reached on a definitive answer to the initial question.

Contextual Notes

The discussion includes references to vector properties, mathematical relationships in SHM, and physical laws such as Hooke's law, but does not resolve the underlying conceptual questions about the negative sign in the relationship.

Yehia11
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In Simple harmonic motion: Acceleration = -W^2 x (W being omega, rads per sec. and x beind displacement (distance if you will) ) Omega is a constant


but why is acceleration proportional to the NEGATIVE displacement, in other words, why MINUS??

Help appreciated. Thanks in advance!
 
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acceleration and displacement are vectors. they have direction. the acceleration is opposite in direction to the displacement and tries to bring it back. hence the minus sign to signify that the two vectors are opposite in direction.
 


yea baner is correct. This is why in simple harmonic motion we have sinusoidal functions representing the displacement velocity and acceleration.

we know that the time derivative of displacement is velocity, and the time derivative of velocity is acceleration.

so if we take the derivative of sine we get a cosine. then we take the derivative of a cosine and we get -sine. That -sine is representative of acceleration, and if you notice it is in the opposite direction of displacement.
 


Yehia11 said:
but why is acceleration proportional to the NEGATIVE displacement, in other words, why MINUS??
To add to what banerjeerupak described, you might find it helpful to consider Hooke's force law (which leads to simple harmonic motion): F = -kx. The negative sign is important. When the displacement is positive, the restoring force (and thus the acceleration) is negative.
 


Yehia11 said:
but why is acceleration proportional to the NEGATIVE displacement,
Help appreciated. Thanks in advance!

Because the spring is elastic, it resists a change in shape
 

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