Re: [Phys-l] projectile motion lab

["Marc \"Zeke\" Kossover" <zeke_kossover@yahoo.com>]

--- FIZIX29@aol.com wrote:

> My high school students will be performing a projectile
> motion lab where they 
> roll a marble down an inclined plane and off of the lab
> table.  
[snip]
> If the line is not hit then I was thinking
> of grades based on 
> fractions of the standard deviation but I don't have a
> good sense of 
> reasonable values.

I make a target -- just a series of concentric circles --
in Microsoft Word. The students then lay the target on the
floor where they expect the marble to hit. I put a piece of
carbon paper (yes, you can still find it at office supply
stores) on top of the target. With the carbon paper, the
ball makes a nice, incontrovertible make on the target. 

This experiment is more difficult than one might expect
though. On my track, the end segment is horizontal. It
needs to leave the table level. Only a few degrees
different can be trouble. The rails at the end of the track
need to be parallel and the same length; otherwise, the
ball will veer left or right. 

I let my students play with a particular release spot up
the track for a while, until they the ball hits where they
predict it will. Then, they switch over to a new release
spot on the track (so that the ball will have a different
exit velocity) for a grade.

Finally, I want to point out that averaging many runs may
not be the best way to reduce uncertainty in this activity.


Marc "Zeke" Kossover

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