User reported issue: tension adjustment in Wave on a String

[oliver-phet]

This is a physics issue rather than a sim issue, so not sure if this is the right point of contact - let me know if not.

Thank you for updating 'Wave on a String' to include numerical values for more parameters. However the parameters don't behave quite as expected: Wave speed seems to be roughly proportional to 'tension', but should be proportional to the square root of tension.

If it's only intended to be a qualitative adjustment - wave speed increases with tension - then of course that behaviour is reproduced correctly, but perhaps the control should revert to 'more/less' instead of a numerical value? Or if the qualitative input is intended (I think it would be nice to leave it in!!), then perhaps the control element could be rescaled?

Assigning to @arouinfar as responsible designer.

[arouinfar]

Thanks @oliver-phet. This sounds like a rather serious regression. The last I reviewed it, the tension was proportional to velocity squared, see #116 (comment).

I'll need to take a deeper look when I have some time.

[brettfiedler]

We shouldn't have touched anything during our 1.2 release to affect this, but I also wasn't looking for it. If it's supposed to have already been designed and implemented, might be worth just asking @jonathanolson to verify current state and check for any regressions in that area of the code.

[arouinfar]

Thanks @brettfiedler! I plan on collecting data in the 1.2 version and comparing to the original data set. If things look amiss, I'll coordinate with @jonathanolson.

[oliver-phet]

@arouinfar has there been any progress on verifying 1.2 data? We received a second email today about this:

I very much enjoy using your simulations in physics courses, and I was happy to see the most recently updated version of Wave on a String to go from just giving options of low, medium, and high to actually giving something semiquantitative with the new value of percent. This would allow students to determine wave speed and plot it as a function of tension to work out that speed is directly proportional to the square root of tension.

However, when I collected data using the frequency and wavelength of the first harmonic, I obtained the following graph:

This gives the characteristic shape of a square root function, but the function isn't looking like it will hit the origin. Transforming the independent variable by taking the square root of tension confirms this:

As you notice, the transformation resulted in a straight line but it does not intersect the origin and therefore does not reflect that wave speed is directly proportional to the square root of tension.

I imagine that this is a simple fix in the code. And if I've done something incorrectly, either because I'm somewhat hungry now or because I'm human, my ego isn't too fragile for you to say, "Look, you overlooked . . ."

I created a chart of sim (version 1.2.1) values, similarly to #116 (comment) and the relationship between Tension and speed squared seems preserved.

I also arranged the chart to match the user's:

So, I suspect maybe just measurement noise? But I'd like @arouinfar to comment before I reply back to the user.