The atwood machine is a device used to demonstrate Newton's second law of motion and other physics and mechanics principles through hands-on experimentation. It's a simple system of two weights suspended by a massless string over a non-stretching pulley wheel. The machine is easy to set up and use, and it's a great way for students and scientists to gain a better understanding of the forces involved in an up-and-down motion with equal acceleration.
When the masses are equal, the Atwood machine stays in equilibrium. This demonstrates that a net force, called tension in the string, acts downward to oppose gravity and prevents any acceleration.
Once the masses become unequal, they accelerate at a constant rate. The heavier mass will fall and the lighter mass will rise. In the ideal situation (massless, inelastic string and frictionless pulley), these two gravitational forces act at right angles to each other, so their net effect is a downward acceleration of m1 equal to g. This acceleration is then balanced by the upward tension force on m2.
To check this, replace one of the masses with another that's slightly heavier. Position the new mass at a different height above the table, and drag it down as far as it will go. Then, measure the height of the other mass above the table. Then calculate the average of these two values for a, which is the acceleration due to gravity. Write this value on your lab worksheets and graph it with a trendline, if you have one.