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Example 3: Uniform Circular motion’s one dimensional projection Understanding Phase Difference through Uniform Circular Motion

Simple harmonic motion can in some cases be considered to be the one-dimensional projection of uniform circular motion. If an object moves with angular speed ω around a circle of radius A centered at the origin of the x−y plane, then its motion along each coordinate is simple harmonic motion with amplitude A and angular frequency ω.

Q1: given that, a circular motion can be described by x = A cos(ω t)  and y A sin(ω t) what is the y-component model-equation that can describe the motion of a uniform circular motion?

A1: y = Asin (ωt)

Q2: When the x-component of the circular motion is modelled by x = A cos(ω t)  and y A sin(ω t) suggest an model-equation for y.

A2: y = Acos (ωt) for top position or y = - Acos (ωt) for bottom position

Q3: Explain why are the models for both x and y projection of a uniform circular motion, a simple harmonic motion?

A3: both x = A cos(ω t)  and y A sin(ω t) each follow the defining relationship for SHM as ordinary differential equations of    d 2 x d t 2 = - ω 2 x and   d 2 y d t 2 = - ω 2 y respectively.

Q4: In, the diagram above, what is the phase difference between blue and magenta color y direction motion?

A4: the phase difference is 90 degrees, or more precisely blue lead red by 90 degrees angle. YouTube: This video shows how a pendulum's oscillations and the shadow of rotating object are related. This could be used to demonstrate that the projection of a circular motion is actually a simple harmonic motion. Run Model:

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This email address is being protected from spambots. You need JavaScript enabled to view it.; Fu-Kwun Hwang

 What is in Phase?





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