For a physics lab, we had to test newton's second law using an atwood machine. Now, as I'm graphing my data, I realized I don't have any uncertainty for the masses. I have been told to make up an uncertainty, yet my uncertainty has to make sense, and I should have a reason. For case one, my masses are as follows: M m 100 100 110 90 120 40 130 70 140 60 150 50 ???? Any ideas?