AlexUjanShaanPulleyLab

Atwood Machine Lab Report by: Alex Clark, Ujan Basu, and Shaan Shakeel



Abstract An Atwood machine is a simple device used for diluting acceleration due to gravity which makes the acceleration easier to measure. The device consists of two unequal masses suspended on opposite sides of a pulley. Gravity acts on both masses but the heavier creates a greater force on the string and lifts the lighter mass as the heavy mass lowers towards the ground. This occurs because of the difference in weight, in Newtons, between the two masses. The heavier mass has a larger weight due to gravity, a greater force, than the smaller mass. The net force acting on the system is therefore pointed down on the side of the machine with the heavier mass, pulling the heavier mass towards the ground.

Introduction In this lab we attempted to find a value for acceleration due to gravity through experimentation using the Atwood machine. This endeavor required that we calibrate the pulley to limit friction. This required the transfer of paper clips from one mass to the other until the lightest touch would overcome static friction and allow the heavier mass fall all the way to the floor. After this calibration we measured the time it took the mass to fall at different mass intervals. By measuring the time it takes for the heavy mass to reach the ground and the distance the mass travels, the speed and eventually the experimental acceleration due to gravity can be determined.

Procedure Data and Graph l
 * 1) Use 2 200 g masses on each side of the pulley. Add 15 paperclips to both sides. More paper clips may be needed but just be sure that the total mass remains constant.
 * 2) Account for static friction in the pulley by transferring paperclips from one side to the other, keeping total mass constant, until the system moves at a constant speed when given a slight push.
 * 3) Transfer 2 more paperclips from the rising to the falling side. There is now a net force acting on the system.
 * 4) Begin experiment with rising mass on the floor. Record the distance from the falling mass to the floor. Record the time it takes for the mass to fall three times, averaging them afterword.
 * 5) Transfer 2 more clips from the rising side to the falling side, repeating step 4.
 * 6) Continue steps 4 and 5 until you have completed 5 trials.
 * 7) Compute acceleration using ∑//F////y//=//ma////y// for each trial. Compare the values.
 * 8) Using the found accelerations plot a graph of acceleration vs. (m1-m2)/(m1+m2). Compute the experimental value for the acceleration due to gravity and compare to the accepted value of 10 m/sec2.



 Results and Discussion When analyzing the results, the data matched the results predicted. This is because as more mass was transferred, the force of gravity on the descending side becomes greater than the force of the ascending side. This causes the net force to be acting downward on the descending side. As a result, after accommodating for friction, the descending side dropped on its own accord and accelerated as time went on. One implication was that as we released the weight, we could not avoid giving the weight a slight push which could have affected the acceleration as it fell.

 Conclusion Calculated value=.010 40% error
 * 1) The advantage of transferring mass instead of just adding on mass to the descending side is that it keeps the mass of the entire device constant. This is important in order to keep the opposing forces the same.
 * 2) Actual value=.014

3. The tension should be the same on both sides because the same force is acting on the ascending and descending side due to the string. 4. The pulley should be light as possible so that opposing forces as are minimal as possible. For example, if the mass if the smallest possible, the drag force will be at its smallest as well.