SHM: Phase Changes & Peter G.'s Experience

[Peter G.]

Hi,

As part of my SHM lessons, I got this sheet today to study Phase Difference. I tried drawing what was asked and I have the impression I got the first two graphs correct. However, I am in doubt regarding the third, mostly I guess, with differentiating what is meant by ahead and behind

Thanks,
Peter G.

(The drawings are really sketches until I understand their shapes properly)

 

[Doc Al]

However, I am in doubt regarding the third, mostly I guess, with differentiating what is meant by ahead and behind

Ahead and behind don't distinguish much when the phase difference is pi.

But your diagrams look OK.

 

[Peter G.]

For the last one, I should really start then showing the curve at the top, correct?

 

[Doc Al]

For the last one, I should really start then showing the curve at the top, correct?

I don't understand what you mean. I thought that last one was for something pi/4 behind the top diagram?

 

[Peter G.]

Yeah, that's what it asks for. So that means it starts like, an eighth of a cycle later? Do you think you could maybe draw a rough diagram on something like paint? I have a hard time conveying this kind of stuff in words

 

[Doc Al]

Yeah, that's what it asks for. So that means it starts like, an eighth of a cycle later?

The diagram would look pretty much like what you drew. It starts an eighth of a cycle 'before' the first diagram. Interpret that like this: At t = 0 the top diagram is already at the peak, while the last diagram takes an eighth of a cycle before it gets to the peak. It's behind the other.

 

[Peter G.]

Ah ok, it's what I thought initially. Thanks a lot for your patience.

 

[Doc Al]

My pleasure. It's tricky stuff.

Check out the diagrams on this page; they may help. (The topic is not SHM, but the principle is the same.) http://www.allaboutcircuits.com/vol_2/chpt_1/5.html"