## Thursday, January 16, 2014

### Science and Stuff

There was a difference of opinion today over one of Travis's physics problems. He had solved it, but when I looked over the work I thought he might want to look it over again. My dad agreed. All parties agreed that an experiment involving the weights and forces from the problem would be sort of fun, and might indicate who was closer to right!

The problem involves two masses and a pulley. The first mass is 12 kg and the coefficient of static friction between the first mass and the table is 0.25. The question is, how much does the second mass have to weigh to start the first mass sliding across the table?
And so...

We weighed books until we had a 12 kg stack. We decided that a fairly smooth table and a tea towel would give close enough to the right friction. And we decided the try the smallest proposed second mass first. If it hadn't worked we'd have worked up to Travis's, which was substantial (more than two large cats, if you can believe!). Fortunately (for the cats, and for us), a larger mass wasn't needed. A large bottle of windshield wiper fluid has a mass of approximately 3.7 kg, and this was enough to to get the stack of books sliding across the table! Travis worked through the problem again, saw his error, and angels sang. Well, assuming that our science was science-y enough, what with variations in the roughness of tea towels, etc. Anyway, it was fun!

But it's not all work around here! (I know that's what you were thinking!)

Emma says Travis is her boy.

Aren't they sweet?

Remember what I said about using cats if we needed a really Big mass?