Science Co-op Week #3

Our video this week dealt with Gravity and as I mentioned in my post about the Science of Disney Imagineering  DVD, the experiment on the disk was a little too ambitious.  There was no way we could build a hovercraft in  twenty minutes.  I chose to focus on some center of gravity experiments instead.

1. The students lined up against the wall with their feet and backs touching the wall surface.  I placed a rock at their feet and asked them to pick it up.  No one could.  In order for us to keep our balance, we must keep our center of gravity over our feet.  When we bend over, we stick our tushes backwards to compensate but that's not possible when you're next to a wall.  As each kid bent forward they stumbled.
2. This time the kids turned sideways to the wall, with a shoulder and one foot pressed against it.  The test was to see if anyone could lift the foot away from the wall off the ground.  Because no one could lean to the opposite side to keep the center of gravity over the planted foot no one was able to do so.
3. I had the kids sit in a chair with its back pushed up to the wall.  A partner stood in front of the chair and was supposed to push 1 finger against the forehead of the sitter, preventing him from leaning forward.  In theory, the sitter shouldn't have been able to stand because his center of gravity was over his seat, not his feet.  The kids were either unwilling or unable to apply enough pushing force to the forehead (perhaps I should have had them use the palms of their hands) and so the sitters were able to lean forward enough to eventually stand up.
4. I turned the chairs sideways against the wall.  A child would lean over the chair with their heads against the wall, lift the chair, and the try to stand up.   This task should be easier for girls, who carry their center of gravity lower than the boys.  Most boys in my class haven't develops big chests and upper bodies so the difference wasn't that extreme.  Then I had the kids wear a back pack and repeat the process.  This time the girls really struggled but the boys could do it easily.