Rick, Thank you for your response to my question about air track
experiments.
In your response you indicate that the applied force is equal to mg.
Surely this is not the force applied to the cart because if it were,
then the forces on the hanging mass would cancel and there would be no
acceleration.
Given this and given that one is trying to demonstrate N2, one can't use
mg for weight anyway since that is N2.
Please correct me if I misunderstood your response.
By the way, whenever I have done this form of N2 (cart with wheels
pulled by hanging mass), most students are invariably confused by the
question as to, for example, whether the acceleration will be constant.
They say "of course it will be constant since falling object accelerate
constantly". I have, therefore tried to avoid the appearance of circular
logic and tried to avoid using falling masses.
David Abineri
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Do your air tracks have an 'air pulley' at one end? If so, a nice set
of
experiments is to use a piece of recording tape to connect a mass and
the
cart in a 'modified Atwood's machine' configuration. Use whatever
timing
equipment you have to measure _accelerations_. Vary the falling mass
(keep
the system mass constant if you want--move mass from the cart to a mass
hanger used to hold the falling mass) then fix the falling mass and vary
the
mass of the cart. You can use this data directly to confirm N2 given
that
the applied force is (mass-falling)xg OR you can assume that the force
is
proportional to the falling mass and try to actually 'derive' N2 from
the
data.
Rick
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David Abineri dabineri@choice.net