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## Physics library

### Course: Physics library>Unit 8

Lesson 1: Simple harmonic motion

# Phase constant

In this video David explains how a phase constant can be used in order to shift the graph of an oscillator left or right. Created by David SantoPietro.

## Want to join the conversation?

• Why S.H.M wave form is generally taken as sine-wave form? Why not cos?
• Well, it can be taken as either. It only depends on the starting condition (posiiton) of the oscillator.

Both cosine and sine waves are sinusoidal
• Shouldn't the phase shift be y=A*sin(2pi/T*(t+phase))?
• That wouldn't make any sense. You would be adding a value in radians/degrees to time. The idea of including the phase constant is to take into consideration the shift between the two waves.
• Suppose we invert the system. Any oscillations possible?
• Do you mean flip the spring so that it is attached to the floor and the mass is attached at the top? The oscillation in this case would be identical.
• Hi, I am a bit confused. How do can I exactly find the value of phi? If it has not exactly shifted 1/4, 2/4 etc of the period?
• forget about algebra and fractions and think about it using trigonometry so like he said in a previous video you can think of a cycle like a unit circle so in the example in this video the sine graph is disphased by a quarter of the period and a quarter of a unit circle is an angle of pi/2 you can review trigonometry and how cos and sin work and what a periodic function
UPDATE 1
your question made think about it more deeply and i made a problem of it to make a formula of how you can determine phi the change of phase and it was a little bit easy so phi = (( 2 pi ) / T) * (X1 - X2)
with X1-X2 is the difference between two same states either a crest or trough or equilibrium
so in generel the change in phase equals two pi over the period, all times the change of time or distance (either you have a graph of time or wavelength which you'll see in next videos)
• So when will we use cosine? Since the phase constant is there to shift the whole wave, what's the use of the cosine?
• What is the difference between phase of a wave and phase constant ? can any one give me the diagram of two waves are out of phase by 270 degrees .
• At , David said, "In this argument of sin in here."
What does the term- 'argument' mean? Any video that'd explain this?
• Basically when you are dealing with a function like sin(x) the X in the parenthesis is the argument to the function.