Rewriting SHM equation from a function of sin(wt) and cos(wt) to just cos(wt-∅)

In summary, the conversation discussed how to rewrite the equation of motion x(t) = 2cos(wt) - 2sin(wt) in the form x(t) = C cos(wt-∅), with the constant C being the magnitude of the sin and cos function and ∅ being found using the formula arctan(b/a). The conversation also mentioned making a substitution and finding the values of x0 and v0 to help solve for ∅.
  • #1
jammydav93
7
0

Homework Statement


Rewrite the equation of motion x(t) = 2cos(wt) - 2sin(wt) in the form x(t) = C cos(wt-∅)


Homework Equations




The Attempt at a Solution


I am able to work out the constant C as it is just the magnitude of the sin and cos function,

C = (2^2 + 2^2)^1/2 = √8

However I am unable to find ∅, can anyone point me in the direction of how to do this?

Many thanks

James
 
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  • #2


Hint:

General equation of motion is: x=Asin wt+Bcos wt. If started from position x0 with velocity v0

x = v0/w sin wt + x0cos wt

Make substitution:

x0 = X sin theta
v0/w = X cos theta
 
  • #3


LawrenceC said:
Hint:

General equation of motion is: x=Asin wt+Bcos wt. If started from position x0 with velocity v0

x = v0/w sin wt + x0cos wt

Make substitution:

x0 = X sin theta
v0/w = X cos theta

Thanks that was all I needed!

Essentially ∅ = arctan(b/a)

Thanks for the help!
 

FAQ: Rewriting SHM equation from a function of sin(wt) and cos(wt) to just cos(wt-∅)

What is the difference between sin(wt) and cos(wt)?

The difference between sin(wt) and cos(wt) is that they represent different trigonometric functions. Sin(wt) represents the sine function, which is the ratio of the opposite side to the hypotenuse in a right triangle. Cos(wt) represents the cosine function, which is the ratio of the adjacent side to the hypotenuse in a right triangle.

How can the SHM equation be rewritten from a function of sin(wt) and cos(wt) to just cos(wt-∅)?

The SHM (simple harmonic motion) equation can be rewritten from a function of sin(wt) and cos(wt) to just cos(wt-∅) by using the trigonometric identity cos(a-b) = cos(a)cos(b) + sin(a)sin(b) and substituting a=wt and b=∅. This results in the equation x = A cos(wt-∅), where A is the amplitude and ∅ is the phase difference.

What does the phase difference (∅) represent in the SHM equation?

The phase difference (∅) in the SHM equation represents the difference in the starting points of the sine and cosine functions. It determines the starting position of the oscillation and can affect the amplitude and period of the motion.

Can the SHM equation be rewritten using only the sine function?

Yes, the SHM equation can be rewritten using only the sine function by using the trigonometric identity sin(a-b) = sin(a)cos(b) - cos(a)sin(b) and substituting a=wt and b=∅. This results in the equation x = A sin(wt-∅). However, the cosine function is often used because it represents the initial position of the oscillation.

How does changing the phase difference (∅) affect the motion described by the SHM equation?

Changing the phase difference (∅) in the SHM equation can affect the motion by altering the starting position of the oscillation. This can result in changes in the amplitude and period of the motion. For example, a phase difference of 0 will result in a motion with maximum amplitude, while a phase difference of π/2 will result in a motion with no amplitude.

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