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Middle School

Forces and Interactions

Atwood Machine

Lesson Description:

Galileo used a ramp to reduce the acceleration due to gravity. In 1784, the Reverend George Atwood, who was a tutor at Trinity College in Cambridge, England, published A Treatise on the Rectilinear Motion and Rotation of Bodies, with a Description of Original Experiments Relative to the Subject. He had devised a way to "dilute" gravity and so to measure g and to investigate the relationship between mass, force, and acceleration. The mass in these experiments is simply the total mass of the weights on both sides. Initially, you'll ignore the mass of the pulley (actually the moment of inertia) and the mass of the string. The force is the difference in mass times the acceleration of gravity. You'll measure the distance that the mass falls and plot it against time to determine the acceleration. You can estimate g, the acceleration of gravity, from the following equation. g = Ma/Δm In the equation, M is the total mass, a is the acceleration you measure, and Δm is the mass difference.