The Sands of Time Flow Through My Cubical

The president of our company just dropped by and gave me the game “I.Q. The Logic Puzzle Game”, since he knows how much I like puzzles. In additional to all the puzzle cards, it comes with an hourglass timer, using sand to count two minutes. This timer has given me an additional puzzle which I haven’t completely figured out, so I am turning here for help.

When you watch the sands drain down against any ordinary background, it appears to be a stream of sand. However, when I view it against my monitor, I can see the individual sand particles falling. Why is this? I assume that it has something to do with the refreshing of the monitor, but beyond that, I do not see why it gives a “clearer” view of the falling sand.


The refreshing of the monitor line by line is creating a strobe effect which is allowing you to see the individual grains more clearly. If you cast your eyes down so the monitor is within your peripheral vision, you can see the slight flicker caused by the refreshing process.

The slight strobe effect that this creates is clarifying what your eye sees as a smooth process into individual “frames” in which you can see the grains of sand.

Hmmm…an interesting and may indeed having much to do with the quality of light on the screen…computer screens and little more than high-faluting TVs. So like TV screens they do not present one continuous image, but rather a series of continuously updating screens in the form of “frames” Your eyes probably are watching 20-30 of these frames on screen per second, so it looks nice and continuous. However, wagging something in front of it, like grains of sand (you can get the same effect by shaking a pencil or whatnot) produces a STROBE effect. You can see the grains of sand better because they are being highlighted by individual frames.

I’d be curious to know if this is the “correct” answer

Thanks for the information… it certainly sounds correct and agrees with the tickle in the back of my mind that said “You’ve seen this effect before…”.

Is it the same effect that makes the monitor image bounce up and down when I’m eating an apple?

No. That’s just the PC getting nervous around an apple. Especially a macintosh.