I took this one a while back during a street fair at the Exploratorium. It’s a reasonably close-up look at a large Newton’s cradle. You know, that little ball/pendulum thingy you sometimes see on office desks? It’s really a demonstration of the conservation of momentum and energy on a smaller, hands-on scale. Physics is cool like that. As for the photo, it doesn’t really fit into any category, so I thought it’d be perfect for this week’s Odd Ball Photo Challenge.