Acceleration due to gravity using Rod pendulum
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Period of oscillations of a pendulum depends on it's length and the value of gravity.
Period of oscillation of a uniform rod about one end is given by
:math:`T = 2\pi\sqrt{2l/3g}`, where :math:`l` is the length and :math:`g` is the acceleration due to gravity.

Objective
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Measure the period of oscillations of a rod pendulum using a photo-transisor and
LED arrangement. The pendulum (T-shaped, a knife edge attached to a 6mm
dia rod) is made to swing between an LED and photo-transistor, connected
to expEYES. The LED and photo-transistor are mounted on a U-shaped
bracket as shown in figure.

.. image:: schematics/rod-pendulum.svg
	   :width: 400px
.. image:: pics/rod-pend-LB.jpg
	   :width: 200px

Procedure
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-  Oscillate the pendulum and click on START
-  Repeat with different pendulum lengths.

Discussion
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The period of oscillation can be measured with an accuracy of 100 microseconds.
However mainly there are two sources of error. The length is measured from the knife
edge to the bottom and used in the formula. But there is a small mass projecting
above the knife edge that is not included in the calculation. Also the
calculations assume that the pendulum must be exactly vertical in the resting
position, which has to be ensured.
