Co-op Science Week 7

Topic of the week:  Gravity.

Began by explaining that while Galileo was figuring out that things always fall down, Kepler was figuring out that planets always orbit around; this looks like it could be two separate phenomena, but Newton figured out that it was all because of gravity.  (Source:  John Hudson Tiner's Exploring the World of Physics).

Listed the 4 forces on the board (strong nuclear force, electromagnetic, weak nuclear force, gravity).  Pointed out that gravity is the weakling of the bunch, that gravity is the only one that is solely attractive, everything with matter has gravity.  Filled glass bowl with water and dropped Cheerios in it bit by bit to illustrate things coming together with gravity (explain that the reason Cheerios clump together, though, is the Cheerio Effect, but it's still a good visual for gravity).  Attempted to explain how forces vary with the inverse square of distance (quicky review of what squares are, quick look at what inverse means).  Pulled out magnet plus a paper clip on string to illustrate how the magnetic force gets sooo much greater when the clip gets closer to the magnet.  Pretty much all of these ideas came from Science Jim's ebook about force, although Science Jim neglected to say anything about the Cheerio Effect, leaving the impression that gravity is attracting Cheerios to each other.

Okay, next,  talked about gravity's pull and how it varies -- Earth's gravity is pulling more on me because I have more mass.  Forgot to talk about how that pull varies by location, although I've mentioned that before in class.  Oops.  Gravity's acceleration is constant, though, as demonstrated in the every-popular flick-a-coin-and-drop-a-coin-concurrently demo, in which the coins hit the ground at the same time (by the way, most places suggest doing this with coins, but I also saw this in a book that suggested using extremely ripe tomatoes -- I'm sure my class would've been charmed, but I really didn't care to clean up afterwards).  Had the kids test each other against gravity by seeing how quickly they can grab a 12 inch ruler dropped between their fingers -- by seeing which inch mark they come closest to grabbing it at, we can calculate how long it took them to react (source for this idea was Science Action Labs -- Physical Science).

Then, wandered off into the subject of center-of-gravity.  We all stood against the wall, heels to the wall, and tried to touch the floor without bending our knees.  We tried grabbing our toes and hopping backward and forward (forward is possible if you scrunch down enough, changing your body shape). 

And then brought out soda cans, water, toothpicks, and forks to start teaching them the skills that will be so valuable in college bars, like how to balance a soda can (or beer can)  on its edge ...

how to balance forks on toothpicks on a salt shaker...

 or else on the rim of a glass, then use a lighter to burn away the excess toothpick.

I'd bought a bunch of extra forks at the Goodwill.  In case you wondered, the Goodwill has more dinner knives than anything else, followed by spoons.  Cheap forks are apparently in high demand.  Although several people felt compelled to comment on my picking through all the forks (I was trying to figure out which ones would work well together) as though they'd never seen anyone buy forks before.

As I was gathering my supplies Rick asked if I had enough lighters for everyone.  "Are you crazy?  These are little kids!"  Of course, as expected, as soon as I got the (single solitary) lighter out I started hearing the speeches like, "Can I use the lighter?  I'm allowed to at home."  "Okay, then, when you go home and do this,  your parents can let you use it if they want. In the meantime, no."

 Theoretically, they all went home and did these things at the dinner table that night.  Optimally they placed bets with older siblings about whether they could do these things, although I forgot to suggest that.