Re: Travel time for different masses travelling down an inclined plane?

You're right in saying that the results of your experiments seem at first
to defy the 
laws of physics.  They seem to but they really don't.  Let's face it,
nothing can 
defy the laws of physics, maybe we just don't quite understand how the laws 
apply.  For our readers, the clarification of this physics problem came
from the 
physics department at the University of Sidney.  The answer to this apparent 
dilemma lies, as you now know, with the fact that the trolleys have wheels.
 Each 
trolley begins with a potential energy of "mgh", looses some of this energy
to air 
resistance, some to friction, and some gets lost in overcoming the rotational 
inertia of the wheels.  Solving this energy balance while neglecting losses
due to 
friction and air resistance, shows that the final velocity is equal to the
square root 
of   Mgh/(M/2+2m) where M is the mass of the trolley, and m is the mass of a 
wheel.  In these calculations I used the moment of inertia of a hoop about
its axis 
to represent the wheels.  Clearly from this you can see if it weren't for
the wheels, 
the mass would cancel out and the final velocity would be independent of the 
trolley's mass.  So in this case the presence of wheels make the difference.

Greg Dries