Wednesday, March 21, 2012
Look what I can do!
I balanced a broom. I got a text message on March 9 that said: "Something is making brooms balance by themselves. It has to be gravity or magnetic pull." Attached were these two pictures:
I've never heard of balancing brooms, and my first thought was 'What?'
So I googled it, and found several 'explanations', which were mostly variants of:
1. Gravitational pull due to either the equinox or an alignment of planets.
2. Something nondescript having to do with solar flare activity and/or the planet's magnetic field.
Both of those sound like nonsense. I mean, why brooms? Why not shovels? The fact that it's only brooms people are balancing tells me the explanation should have something to do with the broom rather than being external to the broom.
I must admit, it looks really wrong for the broom to be standing there all leaned over like that. Before we go on with the broom, let me propose something else to think about:
That's my reading light on its charging stand. It also leans quite a ways over past the base, but it doesn't seem out of the ordinary. Just looking at it, it's intuitive that all the weight is down in the base, and it doesn't seem weird for it to stand up like that. The physics is, if you have an object, no matter if some of it leans out quite a way, as long as the center of mass is still over the base, it stands up.
Back to the broom. The broom is really long, but all the weight is down by the brushy end, the rest is just a hollow plastic tube. We can figure out where the center of mass is by using this simple trick:
If you like people sliding their hands under a ruler set to piano music, here's a longer video. At the end, they unbalance the ruler by taping washers to one end, to show that fingers still meet at the center of mass, even when the center of mass is no longer at the middle.
So I did that, attached a tag where the center of mass is on my broom, and stood it up again:
And what do you know, the center of mass is completely over the base of the broom. So this is really no more strange or mysterious than my reading light standing up - the problem isn't that the broom stands up, the problem is that we think it shouldn't. It's like that thing they tell you in elementary school about how you can balance an egg standing up on the equinox. That's true, but only because you can balance an egg on any day of the year if you're careful enough. The equinox doesn't have anything to do with it.
For the broom, an additional effect comes from the fact that the broom is standing on bristles, which are basically little springs. For it to tip to either side, the bristles on that side have to compress, and their springiness helps push the broom back upright. It's a small push, but it probably accounts for people's reports that they can 'feel' some force trying to make the broom stand up. So not only does a broom balance, but it has a small restoring force to make it more stable.
I left the broom standing almost an hour ago; it's still there. It's just not that hard to balance a broom.
Remind me in a month, when we're away from the equinox and any kind of planetary alignment, and I'll do it again.