P365 Jul10: Laser trace

I was inspired by this (far superior to mine) photo by a US physics student, so tried to do my own version!

I used a bulldog clip to attach my new laser pointer and a weight to a cable that I suspended from a light in our lounge, so that it was just barely above the ground. With the camera on a tripod and the room’s lights off, I gave the pendulum a gentle but firm swing and opened the camera’s shutter. The exposure time varied, but averaged at about four minutes or so.

As the laser swung, the bright point traced lines on the floor that the camera captured. The uneven and erratic path resulted from a number of imperfections in the arrangement: the pointer wasn’t centred relative to the cable, the weight was off-balance and the hanging light to which I hung the pendulum also swung, adding a degree of randomness to the whole equation.

In a perfect world, I’d be able to suspend the pendulum from a very high point, such as a five story stairwell, and I’d be able to add a much heavier, balanced weight. This would result in a much slower swinging motion (due to the pendulum length) and a much longer duration of the swing (tue to the momentum of a heavier weight). If that was possible, then a far more detailed, regular and interesting pattern would propably emerge, like the one in the linked example. It would also be cool if I was able to show the Earth’s rotation as seen in the example. Anyone know of any publicly accessible 5 storey stairwells that I can darken completely and photograph for an hour or two? :)