Strobe light makes water drops fall in slow motion

Using a reciprocating pump and a strobe light, we can make water drops appear to fall down (or up) in slow motion. This illusion is due to the periodic nature of the pump: each droplet forced out of the tube is almost identical to the preceding droplet so our eyes perceive the droplets moving slowly rather than falling quickly. You also can freeze-frame this video and use the ruler to make a crude measurement of the acceleration of gravity. Read more at http://people.cornellcollege.edu/dsherman/waterdrops.html

Category:

Education

Tags:

• strobe
• water
• drops
• illusion

[incargeek]

Thats great!

[derinsherman62]

@incargeek This is but a pale imitation of the great Dr. Harold Edgerton's work. If you really want to see true greatness in action, do a Google search on "edgerton stroboscope techniques" then click on the Edgerton Digital Collections website to view his original device in action with explanation by Doc Edgerton himself.

[Fromzon]

Why didn't you time it in such a way that they seem to float statically without moving up or down? Just asking cause I think it would've been cool :-P

[derinsherman62]

@Fromzon Yes, it would be cool. Unfortunately, the strobe I was using didn't flash at a consistent rate: the flash frequency would slowly drift, so even when the drops started out motionless, they would start to slowly drift up or down after about 10 seconds or so. The solution to this problem is to synchronize the pump and strobe electronically, and that's something I'm working on doing.

[Goatsnarfer]

Why didnt you put your finger under it :(

[derinsherman62]

@Goatsnarfer Simple answer: because I'd get spattered with the fluorescein dye, and I was wearing a nice jacket when I made the video.  I guess the real question is: why wasn't I wearing an easy-to-wash lab coat when I made the video? Darned good question! You should check out the video of Doc Edgerton sticking a pencil into the water stream on YouTube: search for "Waterdrop experiment, stroboscope light" and you'll also see a "motionless saw" cut through a board.

[derinsherman62]

@fruitytuterjjc Neat idea! You could also use a single modulated laser reflecting off a spinning mirror onto a static array of mirrors positioned under each stream of drops. You'd need a computer to control the modulation, but you'd only need one laser. BluRay laser pointers should work well since fluorescein will readily adsorb the blue-violet light and emit strongly in the green. Alternatively, you could use a TEA laser that produces nanosecond ultraviolet light pulses.

[wellthatisgr8]

Awsome, keep,making vids!!!!

[gumdrops27]

Omfg thats amazing

[Goatsnarfer]

@derinsherman62 I sure will, thank you for the answer!