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Lab No.3
Study of momentum of inertia with Maxwell’s pendulum
Objective
study the laws of mechanics for the rigid body by the example of its planar motion
Main tasks
1.
Experimental determination of momentum of inertia for
the
Maxwell’s
pendulum by its fall time;
2.
Calculation
of
momentum
of
inertia
of
Maxwell’s
pendulum
using
the
theoretical formula.
1.
Theory of experiment
Maxwell’s pendulum represents a disk, whose axis is suspended on two turning on
it threads (fig. 1).
It is possible to study experimentally dynamics laws of
translational and rotational motions of rigid body using this pendulum, as well as
the main law of physics − the law of mechanical energy conservation. Having
rotated the pendulum, we raise the disk to height
h
and let go down without push,
then the disk is starting to go down and at the same time to rotate around its
horizontal axis. At the same time trajectory of all points of the disk lie in parallel
plane (surface).
Such motion of rigid body is called
planar
. It can be considered as
the translational motion of the body, which is occurring with the velocity of centre
of mass (centre of gravity, centre of inertia) and at the same time as the rotational
motion around horizontal axes, passing through this center.
The equation of motion for the centre of gravity and rotation of pendulum
relatively to mentioned axes has the following form:
ma = mg – 2T,
(1)
I
= 2Tr,
(2)
where
m is mass of the pendulum, I is momentum of inertia, а is acceleration of
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 Spring '09
 MAMAR
 Physics, Inertia, Momentum

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