Thoughts & questions of the "third grade science" type.

[capri0mni]

Those of you of a certain age will probably remember the educational film strips in elementary science class. Well, now, they're updated into 14-minute and change television episodes. I know this because my local PBS station airs them in the wee hours of the morning so that teachers can video-record them, and bring them into class, and when I have insomnia, I sometimes catch them (and yes, I often get sucked in).

Anyway, the other night, when I was winding down from the tornado scare, I caught a pair of episodes about the six simple machines (Wheel and axle, lever, pulley, inclined plane, wedge, and screw). In these episodes, they defined a Machine as something that must do at least one of the following three things:

1. Make work easier


2. Make work faster


3. Change the derection of work

The first thought that came to me was: Wheel and Axle + Inclined Plane = OTP!!!eleventy!!one!

The second thought came to me the next day, as I caught sight of an old bookbag hanging on a coat hook in the hall, and it was this: Hey, wait a minute! A bag makes it easier to to do the work of carrying thingss. Does that make a bag another simple machine? Then, I figured that it probably didn't as "make work easier" could be just another way to say "reduce the needed level of force," and while bags make things less awkward, they don't actually take up any of the weight you're carrying (the way a pulley or lever does).

Then, just now, another thought popped into my head (I guess my subconscious wasn't quite done with the question): snowshoes!

Snowshoes definitely make it easier to walk in snow. And they do it by changing the direction of the force from a person's weight (spreading it out at a 90 degree angle).

So if Archemedes had lived in a place with deep snow, that needed snowshoes and sleds, would that list of simplie machines have seven things, instead of six? Or are snowshoes simply another version of one of the machines listed above? And if it's the latter, which one?

Comments

[indefatigable42.livejournal.com]

Then, I figured that it probably didn't as "make work easier" could be just another way to say "reduce the needed level of force,"...

Pretty much. In physics, 'work' has a specific meaning. If you give energy to an object you are 'doing work' on it.

If you throw a spear, you're taking an object that has no kinetic energy (i.e. is not moving) and setting it in motion. A spear-thrower
is a machine by your definition. The spear or dart will fly just as fast with less energy produced by the person doing the throwing (or it will fly faster and farther with the same amount of energy put into the throw).

I think as far as snowshoes are concerned, changing the direction that force is applied definitely counts as making work easier. It means the energy that the walker exerts is applied to the walking surface in a more efficient way (which is something the spear-thrower does as well). The walker doesn't get tired as quickly.

The energy given to books when lifting them is gravitational potential energy (i.e. they can give energy back to something if you drop them on it). A bag makes the shape of the weight more convenient (something you can hold in one hand instead of in both arms), but I don't know how much energy your body is producing per second when you are holding books in either of those modes.

Actually, it also means you can carry the books lower (at leg level instead of chest level), so it actually does reduce the amount of work done in lifting them off the floor! It's a machine for picking up books, but not when it comes to carrying them, maybe. :D