megafiddle has it. The only thing the subwoofer is providing here is a means to shake the hose at a controlled shake frequency - that is all.

The hose moving back and forth is flinging the water coming out of the hose. Gravity and flow rate are providing the movement of the water away from the hose.

To answer PG's question, if it were a string, the effect would be less easy to see because there is going to be lots of damping in the string and the fact that the string isn't liquid. When the hose shakes the water in one direction, the water 'globules' separate from the stream. With a string, the molecules are all attached to each other and prevent horizontal movement much more than you get with the water and it's significantly higher mass and resulting inertia.

One can be fooled into thinking that the acoustic energy of the subwoofer is affecting the stream - that is not what is happening in this demonstration at all.

It is simply the subwoofer moving the hose end in translation coupled with the fact that video is not smooth, but sampled in a way, just like audio. The fact that you can't see the hose moving when it's exactly at 24 Hz is because the hose position is in exactly the same spot for each still shot that the camera is taking 24 times a second. The reason the hose looks like it moves at the other excitation frequencies is that the hose is NOT in exactly the same position for each still shot, but slightly off position from the previous shot. The water droplets are not suspended in space, as they appear, but are in the next closest place to the ground on each subsequent frame - but our brains play tricks on us and connect the frames together to give the appearance of movement. This is the whole premise of how video and film and refresh rates work with TVs, CRTs, LCDs, etc. What appears smooth is actually a quick presentation of still images or refreshed screen images. The same applies in the capture of the images as well.

Make sense?

Last edited by rockstar_not; 03/16/13 07:34 PM.
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