# Question regarding projectile motion

I was in physics class a while ago and my teacher had the trajectory of a projectile on the board. he was marking off points on it, and next to each point, right after he marked it off, he wrote 1/2 next to it, then crossed it off while saying "1/2", then proceeded like that, marking off the next point, writing 1/2 next to it, and again, crossed it off and said "1/2". what in the world was he doing? i was zoned out, then when i tuned back in to what was going on I saw him do this, just very briefly, as he was finishing up, then an idea came to me, then left as quickly as it came. I'm trying to get it back. i'm guessing he was doing something with the projectile equations. someone please help. thanks

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.Scott
Homework Helper
I'm guessing there are reading assignments that preceded this lecture and followed it. What kind of trajectories are covered in those readings?
What kind of homework were you assigned?

Do you recall what kind of trajectory was drawn. An orbit? A parabola?

Do you recall the names of any of the other students in that class - so you could ask them?

(I'm sorry - is my attitude showing?)

If you can provide more clues - I (or someone else here) will try to piece it together for you.
Meanwhile, make sure you get enough sleep tonight.

Hi. thanks for the response.
yes. it was projectile motion, so it was a parabola. and it was general physics, regents level. I don't remember the homeworks assigned, but it didn't deviate from the standard pattern, i'm sure of it.
I do remember many names of classmates, but I'm not going to contact them about it, because we lost touch and wasn't really good enough friends with them anyway. besides, it would probably seem kind of crazy. I was 18 at the time of the class. I'm 36 right now.
as for clues, best I can come up with is he was describing the equation for the y position, being v0t - 1/2at^2, because 1/2 is in this equation, and he was marking off points.

I never learned anything in physics class. Just open up a textbook. The university physics textbooks are amazing. They'll tell you everything you need to know

Maybe, the professor was solving for the amout of time the projectile spends above half its vertical distance and the time it spends half below its vertical distance. That’s a cool problem. He was probably talking about half the vertical distance in relation to something.

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Your initial description sounds more like a description of Zeno's paradox. This is sometimes used as a way of introducing ideas for which calculus is the required tool. Alas, 18 years is a long time to try and remember something, so we are speculating on a memory which may not be too representative of the actual event.

Your initial description sounds more like a description of Zeno's paradox. This is sometimes used as a way of introducing ideas for which calculus is the required tool. Alas, 18 years is a long time to try and remember something, so we are speculating on a memory which may not be too representative of the actual event.
but why would he bring up zeno's paradox. it doesn't have anything to do with physics, right?

.Scott
Homework Helper
I was 18 at the time of the class. I'm 36 right now.
Ahhh... I though you were cramming for an exam.
... best I can come up with is he was describing the equation for the y position, being v0t - 1/2at^2, because 1/2 is in this equation, and he was marking off points.
The 1/2 at^2 was the first thing I thought of.

Ahhh... I though you were cramming for an exam.
The 1/2 at^2 was the first thing I thought of.
but how could one account for what he was doing in regards to this? what was he demonstrating?

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.Scott
Homework Helper
but how could one account for what he was doing in regards to this? what was he demonstrating?
He might have been discussing how the vertical velocity changes as you move from the climbing segment to the descending segment... perhaps as a lead-in to computing the location of the peak point in the trajectory.

russ_watters
CWatters
Homework Helper
Gold Member
Perhaps he's just using a trick to draw a parabola...

Initially the projectile moves a distance Y vertically in time T. The next Y is covered in T/2, the next T/4.

Perhaps he's just using a trick to draw a parabola...

Initially the projectile moves a distance Y vertically in time T. The next Y is covered in T/2, the next T/4.
oh, now this is very interesting. please elaborate.

CWatters