Slow motion water drops



We can make water droplets appear to fall in slow motion by pumping them out of a tube using a pump that pushes the droplets out at regular intervals. Many pumps operate at 60 Hz because AC power in the United States oscillates at 60 Hz. If we force droplets out of a tube at 60 Hz and illuminate the droplets with a 60 Hz strobe light, the droplets will appear to be essentially motionless.



If you want to make one of these devices, here's what you need.
If you freeze-frame the movie, you can measure the spacing between the water drops and measure the acceleration of gravity. Each droplet is separated by 1/60th of a second, so the additional distance each droplet moves is due to the speed that the droplet gains in a 60th of a second. This is approximately

(9.8 m/s^2)*(1s/60)^2 = 0.27 cm


so each pair of droplets will be separated by an additional 1/4 centimeter compared to the pair above it.

It is possible to custom-tune the frequency of a low voltage pump to match the frame rate of either a strobe or a high-speed digital camera. I've done this using a Gorman-Rupp model 14825-710 pump that normally runs at 19 volts AC but also runs fine at pulsed 24 volts DC when connected to this circuit based on a 555 timer chip.