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PART 5:
This one’s called “Choke up on that Bat.” When I was coaching baseball with little kids
(because I don’t really know very much about baseball), you would watch a kid with sort
of a fast pitcher, and he would be up there with a bat, and the pitch would come around,
and the kid would kind of swing slow, and he’d be behind it, and the first thing that
everyone on the team says is “Choke up on your bat!” except some people don’t know
what that means, so who doesn’t know what it means to choke up on a bat? Everybody knows.
Ok. So here’s how you normally swing a bat. And choking up on it means choke up on it
a little bit higher. Now why in the world would you do that? The answer is based on
what it takes to get things to move. This ball will not move anywhere unless it’s
given a push. And this bat will not rotate unless it’s given a twist. The more massive
the ball is, the harder it is to move, the more inertia it has, we say. That’s true
of the bat too. The heavier the bat, the harder it is to swing, but it’s also true that
the more the mass is distributed away from where you’re trying to rotate it, the harder
it is to swing. So, it’s easy to swing a bat like this. It’s not so easy to swing
a bat like this. So if you grip it a little bit higher, and by the way, you may think
that when you’re batting, your body is doing all the twisting. If you do it a few times,
you find out, that’s not true. Your wrists are doing all the twisting. Your wrists start
from way back here, and they end up way out here, like 180 degrees. So it’s all rotation
in the wrists, and if you move up the rotation point a little bit toward the mass, it’s
easier to rotate, therefore you can get around faster for a fast pitch. Ok? That’s the
idea there.
Two more. One on the topic of “FAST”. We know that kids love to talk about who’s
the fastest, what’s the fastest thing you’ve seen, what’s the biggest thing you’ve
seen, what’s, you know. Comparisons are a big thing for kids. So the idea here was
just to talk about what speed means. Define it, how we actually measure it as distance
divided by time, and then to talk about things that are fast. Here’s the fastest land mammal,
a cheetah, and it’s very, very fast. But there’s a chart down here that shows where
a cheetah stands. Relative to a three-toed sloth is pretty fast. But relative to the
Earth in its orbit around the sun, not so fast. And relative to the speed of light,
which we talk about here as the ultimate speed limit in the universe, it’s tiny indeed.
It’s particularly instructive and perhaps slightly difficult as well to explain this
plot to students, because the speed of a three-toed sloth is on this scale 0.15 or something like
that, and on this scale the speed of light is 186,000. You can’t make a graph like
that very easily on a linear scale, so this is a logarithmic scale plot, and it involves
a little bit of discussion about the fact that to go from here to here to here isn’t
a step of one, it’s a factor of ten. The jury’s still out on whether or not we’re
going to have to revise this poster, given the recent work on identifying neutrinos,
that potentially they are faster than the speed of light.