PURPOSE: To illustrate the Second Law of Motion and to experimentally determine the acceleration of gravity.

DESCRIPTION: Equal masses M of 200 grams are hung on the ends of a light string passing over a light, frictionless pulley. When a small additional mass m is hung on one end, the resulting acceleration can be measured by timing the motion of either mass over a distance S between two points. The acceleration of gravity g can then be calculated:

g = a (2M + m)/m,

where a is the acceleration of the system:

a = 2S /t**2.


REFERENCES: (PIRA 1G10.40) See Demonstration Reference File for helpful background papers as well as the famous story of the bricklayer involuntarily using the Atwood machine concept.

EQUIPMENT: Atwood machine on stand with two 200 g masses, set of small masses, manual timer, as assembled for photograph.

SETUP TIME: 5 min.

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