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PART 8:
So here’s an example:
Baseball Kid in Video: Hi! Welcome to STOP for Science!
Kid #2: We’re here at Section School in Mukwonago, Wisconsin.
Kid #3: And we’re going to find the velocity of our pitches.
Bob: (laughter) This is one of the classroom activities that Pat’s going to explain to
you. It has to do with figuring out the speed at which the students can pitch a ball. Obviously
it has to do with “How Fast is FAST?” At that particular speed, you can capture
it by taking video of it. So if you want to go ahead and explain how…
Pat: Right, so this is one of the suggested activities for the “How Fast is FAST?”
poster, and it works as follows: It is based on the concept that is explained in the poster,
that speed is measured as distance over time. Bob is the one who filmed this. We had students
who pitch a baseball. And we measure how fast that baseball is going the following way:
We need to know the distance. Well, we can measure the distance from where the pitcher
is to where home plate is. In this particular example it’s about 30 feet from the pitcher’s
mound to the plate. You can look at about where this pitcher is releasing the ball as
perhaps 2 feet ahead of the mark. So actually, if I remember correctly, it was 32 feet to
the pitcher’s mound, so we’re estimating that as 30 feet that the ball travels. So
all you need to do is watch the student throw the ball and sit there with your little stopwatch
or a timer and go “START-STOP!” and measure it, and that’ll obviously be incredibly
accurate and you’ll get the answer. In reality, no, it’s not true, because it goes pretty
darn fast. Let me show you.
Ok, so, here’s the pitcher. Imagine yourself with a stopwatch, okay? It’s pretty fast!
So what you can do though is take your video camera, film this, put it into your favorite
viewing program (this ended up being displayed in Quicktime), and then pause it, and step
through and watch the pitch. By the way, this kid’s got amazing form. It’s true, look
at it! But the ball is leaving his hand right here, right? So one, two, three, four, five,
six, seven, eight, nine, ten, eleven, twelve is right when it’s crossing the plate. Twelve
steps in the movie, right? So all you need to know is how long each one of those steps
is. You see, or you might be able to see, that right down here in the corner, there’s
a little thing that counts out how many seconds long the video is running. So if we just go
to where it is changing from one to two here, and then we count how many steps it takes
to get to three, so we’ll know how many frames it is to go one second. One, two, three,
four, five, six, seven, eight, nine, ten, eleven, twelve, thirteen, fourteen, fifteen,
sixteen, seventeen, eighteen, nineteen, twenty, twenty-one, twenty-two, twenty-three, twenty-four,
twenty-five, twenty-six, twenty-seven, twenty-eight, twenty-nine, thirty, there, it changed to
three. So it takes thirty steps to go one second in this thing, okay? And that’s all
the information we really need. We figured out that it took twelve frames. We counted
out that that’s how long it took for it to go thirty feet. Each one of those frames
is a thirtieth of a second. So it took 0.4 seconds for that pitch to travel thirty feet.
And so we can calculate that thirty feet over 0.4 seconds is 75 feet per second. And we
can convert that to miles per hour if we want to do that, and it turns out that he’s pitching
at 51 miles per hour, which the kids of course are thrilled to find out.
Bob: He happens to be a twin. His whole goal is to be able to pitch faster than his twin
brother.
Pat: That’s right, the most important thing here is two students! (laughter)