How does the Hydra Lamp work? If you haven’t seen it yet, it’s a newish consumer device in which water drops flow or appear to flow slowly upward. See a video of a cat interacting with the device here. Their website FAQs say only that “The Hydra Lamp uses accurately timed lighting to create an anti-gravity effect.” That doesn’t provide enough detail to satisfy my curiosity.
Is this similar to the trick used in Now You See Me 2? Where they have water dropping really fast, but shine lights on the droplets at just the right time that you see it going backwards; a variation of the stroboscopic effect.
~Max
It’s sputtering out discrete drops of water at a fixed rate; we’ll say 10 per second as an example. They illuminate the drops with a strobe light, which tricks your eye into only attending to the brightly lit intervals and ignoring the periods in between the strobe flashes when then drops continue to fall. If they hit the strobe at 10 flashes per second, you will see the drops appear to hover in midair - they don’t actually hover, of course. With each flash, a drop has moved from one position to the next one down, and been replaced by the following drop. The drops look identical, though, so you think the same drop is staying at one spot the whole time. Under bright enough ambient light the effect would be lost.
To make the drops climb or fall slowly, just detune the strobe slightly, to say 10.1 flashes per second. Now each drop falls just a bit more per flash, so the whole train seems to be gliding downward.
It uses a strobe light. Very fast light pulses that look like steady light, but are not.
See this video: The Strobe Light Effect (Levitating Water Experiment) - YouTube
Thanks, folks. That makes sense. I should have thought of it myself, because now that you mention the strobe effect, I do remember the old Straight Dope column that discusses it: How come the wheels of a moving car appear to rotate backward sometimes?
It’s not only motion that is distorted, but so is energy. When the cat gently taps a drop it breaks up and flies off a lot faster that one would expect for such a seemingly slow moving thing.
Or rather, the (appearance of) energy isn’t distorted at all, despite the extreme distortion of the (appearance of) motion.
What is distorted is the appearance. I felt no need to include extra words.