Pitch of a guitar string and a rubber band...?

Question

Why does the pitch of the guitar string goes up when u tighten it..but the pitch of the rubber band stays the same or goes down.why?

Answer 1

It doesn't (the rubber band). But, depending on how you stretch it, you can stretch one part and (without noticing it) slacken the other. So you get a higher and shorter note from one bit, and a lower and longer note from the other. This may account for it. If you strech it really tight you'll see the pitch will go up as you stretch it more, not so easy to do with just two hands, i recomend a foot or inanimate object to hold one end.

Answer 2

The pitch is dependent upon 3 things.

Unit mass or m/l (mass divided by length)

Tension

Length



Logically a guitar string under tension will not increase greatly in length, it is not as boingy as a rubber band. The rubber band however, dependent upon it's makeup, can increase enormously in length.



It is quite complex to work out three parameters that change but that's the problem we have here.



So f=(√ (T/(m/l)))/2l



This is assuming a half wavelength. As you see from the formula if we double the tension and the band doubles in length for example, the top line of our equation remains constant, when we root it and then divide by double the length we have affectively reduced the frequency.



The main consideration here is "How boingy is your rubber band?" i.e. how much does it stretch in comparison to tension. Extremes would have a rubber band act just like a guitar string, for example when there is very little stretch left in it, you measure the frequency of the wave and then apply a tiny bit more tension, almost to breaking point. At this point the band is nowhere near as stretchy as is was in it's rest position and would very much act like a guitar string, the pitch (or frequency) rising. Now consider the alternative extreme. Double the tension, 6 million times the length.........



Hope this helps.



http://hyperphysics.phy-astr.gsu.edu/Hbase/waves/string.html



This might be useful for the formulas

Answer 3

hmmm... that's gotta be a strange rubber band if it doesn't go up in pitch when you stretch it.

Answer 4

Ding Dong thats the sound it makes.. :)