Type of mechanism is mounted on the living room?

[jaquecusto]

http://sbtvd.anadigi.zip.net/images/camara.JPG
http://sbtvd.anadigi.zip.net/images/camara2.JPG

A student walks into a room with a groove on the ceiling. Turning off the lights, he sees a shadow moving the floor. With only a ruler and a stopwatch, the student is able to determine what type of mechanism is mounted on the living room?

 

[JaredJames]

Is there more to this or should I just make something up?

 

[jaquecusto]

More explanations:

In the first condition, the mechanism is a pendulum at normal oscilation. In the second case, the mechanism is a rotary wheel with single radius.

I suspect about student conclusion:
"In the both tests, by the shadow, it's impossible to determine the velocity and position of moving sphere at same time" :)

 

[vanhees71]

Well if the student is a gifted experimentalist with accurate enough ruler and watch, he could check whether the motion is harmonic. If it is, it must be the rotary wheel, otherwise the pendulum.

 

[Vanadium 50]

Or the reverse.

 

[jtbell]

Well if the student is a gifted experimentalist with accurate enough ruler and watch, he could check whether the motion is harmonic. If it is, it must be the rotary wheel, otherwise the pendulum.

(emphasis added by me)

Or the reverse.

Hint: does a pendulum really undergo simple harmonic motion?

(and has the OP's course discussed that point explicitly?)