Convinced despite naysayers: human finger beats sound!

[hefner]

When you snap a long whip, the loud crack heard results from the tip material moving (through air) in excess of the speed of sound. This is well known.

I have in turn surmised that when you snap your finger, the noise results from your fingertip moving in excess of the speed of sound. I've posted about this before, here and elsewhere, and nobody seems to agree. But that noise is clearly NOT created by your middle finger slamming against the base of your thumb, no! When I snap my fingers (learned late in life) it's a fairly soft/awkward landing made against the base of the thumb.

No, I am still convinced. Heck, it's only about 750 MPH that we're talking about. The whip end achieves it and I believe that the human physiology also can and does move that fast to make the noise.

I'm not closed-minded entirely, but I stand convinced at this time.

[orbsycli]

that's radical.
what does hypography have to say about this ?

[Tormod]

Snapping fingers simply moves air and produces sound. Different sized fingers, different speeds, and different force all produce different sounds - this is easy to test.

While the comparison between the whip and a snapping finger may seem logical, the original post offers no evidence. So I don't know what it is that Hefner is so convinced by. He should device a demonstration which could be used to test the speed of the snapping fingers.

Since we have the ability to multi-snap, we should (according to Hefner) theoretically be able to make many more than 12 snaps per second...

How to Multi Snap - wikiHow

[Turtle]

Originally Posted by hefner

...
I have in turn surmised that when you snap your finger, the noise results from your fingertip moving in excess of the speed of sound. I've posted about this before, here and elsewhere, and nobody seems to agree. But that noise is clearly NOT created by your middle finger slamming against the base of your thumb, no! When I snap my fingers (learned late in life) it's a fairly soft/awkward landing made against the base of the thumb.

No, I am still convinced. Heck, it's only about 750 MPH that we're talking about. The whip end achieves it and I believe that the human physiology also can and does move that fast to make the noise.

I'm not closed-minded entirely, but I stand convinced at this time.

Here's an experiment you can try yourself that may convince you otherwise.

Originally Posted by Jim Swenson

And you can try for yourself: snap your fingers but be sure the finger misses the palm. Or insert some padding on your palm, near the base of you thumb. A band-aid might work. A folded tissue has some effect for me.
Your thumb and finger are doing the same friction and fast break-away, but much less sound results. And only the slapping point of finger on hand has been changed.

Snapping Fingers

[Jay-qu]

In addition I would like to add that the human finger is much much shorter than your avg whip! The length of the whip gives you leverage when trying to make one end travel as fast as possible - and its still not easy to do!

[jab2]

Hefner, as is said, I am also not to clear on what you are sure about, but if it is that the sound of a snapping finger is created by you fingertip going through the sound barrier and not the violent impact of the index finger tip landing on the thumb base, you only have to put a piece of cloth on the landing area to hear a totally different and attenuated sound. As you have only modified the landing area and not the speed or trajectory of the fingertip in this simple experiment, it should be clear that the sound is generated by the landing and not the travel.

If you however mean that the air displaced by the index fingertip moves faster than sound much like the snapping shrimp (I think that's the name), it would be more difficult to prove. I suppose one can use the fact that the speed of sound changes with air pressure and devise an experiment that look at the profile of the sound wave in different air pressure situations. Or am I talking s%^&?

[hefner]

I did the bandaid test and the snap did NOT soften any. No, I'll argue, the sound of air being moved around is mostly silence, especially for something as small and aerodynamic as a finger. Sure, noise could issue and we'd fully expect that to be a WHOOSH. So you might argue that a sudden burst of acceleration to great speed changes a whoosh to a snap? It could happen maybe depending on how steep the acceleration and how great the final speed. But I am likely convinced that whoosh becomes snap only when the sound barrier is broken. Um, yes whips are long, resulting in good leverage; but we also possess good leverage using the brief build-up of muscle tension just before the snap.

[Pyrotex]

Speed of sound. 650 to 750 MPH depending on air pressure. If we pick 681 MPH, that works out to 1000 feet per second.

Let's figure that middle finger tip goes through 4 inches during a snap. Being very conservative, let's assume that the finger tip goes from a speed of zero to 1000 ft/sec in the entire four inches, and then hits the base of the thumb, where it goes to speed zero in half an inch (indenting the flesh temporarily). The finger tip achieves the speed of sound only long enough to give the characteristic "sonic boom".

NOW. Two things occur to me.

1. The "sonic boom" if graphed out -- volume on the Y-axis, time on the X-axis -- always looks like a very sharp spike, with a more gradual trailing edge. It is, after all, a shock wave. See the chart a page or two down the given link. These sonic booms are very sharp, like "cracks" or pistol-shots. The finger-snap, on the other hand, does not have this sharpness. It sounds like a small thud. It would graph like a normal distribution, gradual on both the leading and trailing edges.

2. What acceleration is necessary to get from 0 to 1000 ft/sec in 4 inches or a third of a foot?
Distance = 1/2 * Accel * Time^2

therefore, [1] Accel = 2*D/T^2

We need Time, so we remember that Distance = Velocity * Time
or, if Velocity increases linearly from zero, then Distance = 1/2 * Velocity * Time

so, Time = 2*D/V

2*D is 8 inches, or 2/3 of a foot, so

Time = (2/3) / (1000)
= .000666 seconds

Going back to equation [1]

Accel = 2*D/T^2

A = (2/3) / (.000666)^2 = approx 1,500,000 ft/sec^2

A G of accelleration (what we feel from gravity) is 32 ft/sec^2

So, you would have to accelerate your finger tip at nearly 47,000 G's.

If your finger (upper two joints) weighs just one ounce, then we are talking about a muscular force of over 2,900 pounds.

And deceleration of your finger tip back to zero (over the course of 1/2 inch) would be 8 times harder, or over 11 Tons!!! That would smash your hand to jelly.

Check my math, because Lord knows, I could have made a mistake.
But I have serious doubts that anyone can exert more than a Ton of muscular force on their middle finger.

[Pyrotex]

Originally Posted by hefner

...I've posted about this before, here and elsewhere, and nobody seems to agree. ....

Yes, several years ago, in fact. http://hypography.com/forums/physics...html#post41420

[hefner]

Originally Posted by Pyrotex

...The finger-snap, on the other hand, does not have this sharpness. It sounds like a small thud.

That is patently untrue! ..it sounds extremely sharp and crisp and loud, when done expertly.

As for your arithmetic rebuttal, I'll only venture that yes, you can and do achieve the necessary force and speed. I mean, isn't it obvious now that Jab2 has brought up the "snapping shrimp"?? I had never heard of the creatures, but if it's a known fact that they break the sound barrier with their muscular twitch, then it's not at all unreasonable to think we too can achieve this. Obviously the shrimp uses its twitch for propulsion thru the water, and it would only snap when caught and brought up in a net. Then its twitch becomes a frantic one indeed.