Atwood Machine

An Atwood’s machine is two masses connected by a strong light string that are hung over an ideal pulley (light and frictionless). The masses have identical velocity and acceleration magnitudes at every instant. If we define up on the left and down on the right as positive directions, then the masses have identical velocities and accelerations period. This simplifies the analysis a lot.

The most natural choice that makes up on the left and down on the right positive directions is to focus on the pulley. Up on the left and down on the right are the same to the pulley – both are clockwise rotations. This the coordinate system to use for this problem.

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Let’s look at the clockwise forces that act on the system of two masses and the affect they have on their acceleration.

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An Atwood’s machine has m1 = 1kg, m2 = 2kg, hung from an ideal pulley. What is the acceleration of the masses? Calculate the tension in the string attached to each mass.

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