Thursday, April 15, 2010

Real read world physics problems

If you haven’t seen the classic video “Real World Problems from my Physics Book” on Youtube, it’s worth the 3 minute and 10 seconds.



Amusing, yet poignant.

Well, ArtieTSMITW, here is a real world problem for you.

A few weeks ago, as I was backing out of a parking spot at work, I heard a noise. My noise making skills aren’t nearly as developed as those of the Car Talk guys, but it sounded like a cross between a rattle and a “ping ping ping”, although not as high pitched. The last time I ignored a sound in my car, pieces of it fell out as I was driving, so I decided to do a few laps around the parking lot before heading into DC traffic.

Here is what I noticed
-Nothing was dragging behind my car
-The sound was most pronounced when I was just starting to move, or just coming to a stop
-The noise went away when I was stopped completely
-The noise went away when I went above 5 mph or so

Any ideas?

I’ll give you a hint…I had my tires rotated a day or two before.


It turns out that the mechanic forgot to tighten one of the nuts on my rear, passenger side tire. The nut had come off and was rolling around inside my tire. (I didn’t figure out the problem until I consulted with a friend later that night. I just turned up the radio and tried to stay over 5mph all the way home.) Luckily it was only one, the rest of the nuts were tight.

Whew! That was an easy fix. But it did get me thinking about a similar “real world” situation that is in every introductory physics book I have ever seen. It starts something like this,

You swing a pail containing a mass m of water in a vertical circle of radius r…

The object of the situation is not to get wet. So, students are usually asked to find the minimum speed with which you should swing the bucket around your head in order to avoid getting wet. Spin it too slowly and the water will fall out of the bucket when the force of gravity is greater than the centripetal force. Spin your wheels to slowly and the nut will rattle/ping its way to the bottom.

It's a rite of passage problem, and kind of an interesting one, at least to me. But then I started thinking about it from ArtieTSMITW’s point of view…that would be an amusing video. This guy got it right, but I imagine this wasn't the first take.



Maybe a loose nut in your tire is a more likely situation than swinging a bucket over your head, but that video sounds boring even to me. It's definitely important to put physics in real world context for people when we can, for reasons like motivating students to learn physics, demonstrating career opportunities for people that can do physics, and encouraging public support ($$) for physics. On the other hand, forcing necessary problem skills into real world situations can sometimes turn out just ridiculous.

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