There was a question in my physics that I was stuck on... It said someone was holding a ball, with his arm at a right angle so his lower arm was parallel to the floor (it had a diagram, it's simpler than you think), and the ball weighed a certain amount, the biceps connected to the lower arm at this point at this angle, and I had to find what force the biceps and the humerus (upper arm bone) were exerting. It turned out it assumed the lower arm doesn't weigh anything and didn't put that in the equation (which it had done things similar to it in the past)...