EM-14 Atwood's Machine
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Atwood's Machine demonstrates the combined effects of linear and angular accelerations. A string carrying two weight holders passes over a large pulley. The linear inertia and the rotational inertia of the system are equal; therefore, both mass and moment of inertia must be considered in calculating the acceleration. . The acceleration is produced by adding light weights to one of the weight holders. The pulley can be removed from its support to measure its moment of inertia. The experiment is started by dropping the platform and releasing the weight holder. The pulley is marked with 18° spokes which pass in front of a Photogate. The signal is connected to any of the popular computer interfaces to measure and store the time intervals between spokes on the pulley. Plotting the angular velocity computed from this data versus time gives an accurate measurement of the angular acceleration. The required measurements can also be made with a simple stop watch. |
EC-14 Digital Photogate
Atwood's Machine was originally designed to be timed with a pendulum clock. The required time measurements can still be made with a stop watch. Still it seems negligent not to apply advanced timing systems to this classic experiment. Adding a miniature Photogate to view the wheel as it rotates lets us send a digital signal to a computer for recording and analysis. The wheel is marked with ten black stripes so that as it rotates, a series of pulses is sent to the computer. The signal can be stored by the popular computer input modules such as the Daedalon Computer Timing Interface (EC-40). The tiny Photogate is fastened with two screws to the wall bracket and can be attached in a minute. |
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