My last one, I promise.
When I stumbled upon Mr. Grimes' paper regarding all of these guitar applications to physics, I had already known that things like harmonics had to do with basic string/wave physics - but all of these other applications have really interested me, as someone who loves the instrument. If you're interested at all, visit the source material; he obviously worked very hard on it, and his hard work shines through.
This final post focuses on yet another vital guitar technique that is prevalent in so many solos - Hendrix and Van Halen were masters at it, and Stevie Ray Vaughan's subtle uses of the tremolo bar added so much character to his already impressive blues playing.
The whammy bar in a typical Fender Stratocaster fits directly into the bridge as shown above, and by applying a torque to the whammy bar, the bridge experiences a slight rotational acceleration in order to change the frequencies of the strings. As we know, a force exerted closer to the bridge would provide less torque, and thus, less rotation. However, apply that same force near the bend in the bar (close to the white tip), and your torque is significantly greater. (Net torque equals force times length.)
The whammy bar equation is essentially identical, except in the numerator of that radical fraction, the force applied to the whammy bar (F subscript W) is added to the tension of the string. The plus and minus indicates that the whammy bar can go both ways, although on the typical Stratocaster, it is much harder to pull up on the bar and raise the pitch than it is to depress it and lower the pitch.
If you don't have a locked-in bridge, though, you're not likely to use this tool as frequently - otherwise, the forces applied onto the bridge alter the tensions of the strings, in other words making them very out of tune. For those using a Strat, remember to whammy in short bursts and with much smaller rotational forces, so that you don't have to stop to tune in the middle of a song.
Grimes, David R. "String Theory - The Physics of String-Bending and Other Electric Guitar Techniques." PLOS ONE:. N.p., 23 July 2014. Web. 23 Nov. 2014.