Slowing down time can help

Most science centre professionals will agree that the best way of experiencing a phenomenon is to observe the real thing, or better yet, get hands-on with it. That’s what science centres are all about.

A good example is the Science Centre Singapore’s Strobe Fountain exhibit that demonstrates the stroboscopic effect with real water droplets, right in front of your eyes, and with a knob to change the strobe frequency and directly observe the effect of that.

That’s very engaging and certainly better than watching a video, for example. But when it comes to explaining how the effect occurs, the exhibit is less than ideal; The phenomenon itself – water droplets apparently suspended in mid-air and slowly moving up or down with varying strobe frequency – is not self-explanatory, and the text explanation is rarely effective in helping people understand what’s going on. It helps if there is someone there who can explain the effect verbally, like in this youtube video. But even then you need to imagine the process, because you can’t observe it in real-time. If only we could slow down time!

That’s where online simulations come in handy. The interactive visualisation below allows you to slow down the animation to almost a standstill, so you can really see what’s going on. You can adjust the strobe interval (the time interval between flashes) just like in the real exhibit, and you can turn on the ambient light so you can follow the droplets between flashes.

  Controls: (Click on applet to activate it.)
       l - switch the ambient lights on and off
    s, x - increase/decrease the strobe interval
    f, v - increase/decrease the frame rate of the animation

The best experience would be to see the real phenomenon, have somebody explain it, and then play around with an interactive visualisation to really understand the effect… In the absence of that, and if the above hasn’t clarified the phenomenon yet, here’s the textual explanation provided on the webpage hosting this online exhibit:

The Strobe Fountain exhibit is based on the stroboscopic effect. Under normal light, a falling droplet is visible all along its path, and we perceive it as a falling droplet. Under a stroboscopic light – which is darkness most of the time with brief flashes of light at regular intervals – the droplet is falling in darkness and illuminated every few milliseconds.

If it was a single droplet, we would see it jumping through a sequence of illuminated positions as it falls. The trick here is that we don’t just have one droplet but a continuous series of droplets falling one after the other, with more or less equal distances between them (at any given position in the path). So while the first droplet has jumped to the next position, the second droplet has replaced the first one where it was before – if the regular timing of the flashes matches the regular sequence of droplets, that is. And because the droplets all look more or less the same, we perceive the succession of droplets appearing in the same spot as one droplet suspended in that spot.

If we now slightly change the time interval between flashes (ie the strobe frequency), we can make those apparently suspended droplets move slowly up or down. If the interval is shortened, the droplets don’t quite reach the positions of their predecessors by the time the next flash occurs, so we see the positions of the suspended droplets slowly moving upwards.

There are more online exhibits where this one came from.

2 Comments Add yours

  1. Sanjali says:

    Wow, that’s pretty interesting! This interactive visualisation experience really brings the entire exhibit up a notch!

    I will definitely take a look at those other online exhibits you mentioned, thanks for sharing Andy!

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