The Atwood Machine
In the foyer of the Physics Department at the University of Barcelona you will find, as well as a fine refracting telescope, an example of the Atwood Machine. For some years before my current sabbatical I have been teaching Newtonian Mechanics to first-year students in Maynooth and used this as a simple worked example. I have to admit I’ve never seen an actual Atwood machine before, and what I’ve done in lectures is the simplified form on the right rather than the actual machine on the left.
The illustration on the right depicts the essential elements, but you can can see that the actual machine has a ruler which, together with a timing device, can be used to determine the acceleration of the suspended mass and how that varies with the other mass. You can work this out quite easily in the simplest case of a frictionless pulley by letting the tension in the string (which is light and inextensible) be T (say) and then eliminating it from the equations of motion for the two masses. I leave the rest as an exercise for the reader. A more interesting problem, for the advanced student, is when you have to take into account the rotational motion of the pulley wheel…
In the Dark 
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