Position in Motion: When to Use Cos & Sin in x=A*sin(wt+phi) or x=A*cos(wt+phi)?

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Discussion Overview

The discussion revolves around the formulation of the equations x=A*sin(wt+phi) and x=A*cos(wt+phi) in the context of motion. Participants explore when to use sine versus cosine functions based on initial conditions and the representation of waveforms.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • Some participants suggest that the choice between sine and cosine functions depends on the initial conditions of the motion being described.
  • One participant notes that if the object is at x = 0 when t = 0, using a sine wave is more straightforward, while a cosine wave is preferable if the object starts at maximum displacement.
  • Another participant mentions that the phase factor can be adjusted to use either sine or cosine in any situation, indicating flexibility in the choice of function.
  • A question is raised about finding the phase factor by setting x=0, implying a method for determining the appropriate phase shift.

Areas of Agreement / Disagreement

Participants generally agree that the choice between sine and cosine is influenced by initial conditions, but there is no consensus on a definitive method for determining when to use each function beyond these conditions.

Contextual Notes

The discussion does not resolve the specifics of how to find the phase factor or the implications of different initial conditions on the choice of sine or cosine functions.

Tricks67
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In what kind of cases do u we formulate the equation type x=Asin(wt+phi) or x=Acos(wt+phi)...and if for example we use it to define the position of some thing in motion when do we know when to use cos and when to use sin...?
 
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It doesn't really matter which you use. The only difference is what position on the wave corresponds to phi = 0. A sin(wt+phi + pi/2) = A cos(wt+phi)
 
Tricks67 said:
when do we know when to use cos and when to use sin...?

It depends on the initial conditions for your specific situation. If the object is at x = 0 when t = 0, then it's easiest to use a sine wave. If the object is at x = maximum (i.e. the amplitude) when t = 0 then it's easiest to use a cosine wave.

However, as AlephZero noted, you can use either kind of wave in any case, by including an appropriate phase factor.
 
and we find the phase factor by setting x=0, right?
 

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