I had a teacher once who used his hourglass whenever he was asking a question. You had all the time in the world to answer, and by that I mean the whole 3 minutes it took that sand to disappear. And that's nowhere near enough time to answer all the questions he could come up with.

While I am sure he still uses the same hourglass, I have here an application he might be interested in. Gravitation is an application for Symbian devices that pack an accelerometer. And how many such handsets are there?

Install it on the Nokia 5800 XpressMusic and start simulating those hourglasses. Select the time and tilt the device in order to get the virtual sand moving. Here's a video of Gravitation v1.0 and here's where you can get more info and download it from here.