1. The problem statement, all variables and given/known data I need some help with a Physics lab. My teacher wasn't there the only chance I could ask him. I don't understand how to prove that the net force is zero when you have the three forces in different directions. For example, the first force is 9.7 N [down], the second is 5.3 N [right 46 up] and the final is 7.4 N [left 60 up]. Also, how do you calculate the inaccuracy rate? (eg. [tex]\pm 0.02[/tex]) 2. Relevant equations When you come up with your answer, how do you know if it is a successful experiment? I know that it should be approximately zero, but I saw somebody doing the same experiment had a result of 102 and he said it should have been smaller than 86. That's a bit far from zero, which confused me. 3. Attempt at the Solution Well, I know that the sum of all the forces in equilibrium is zero. So, this means that =9.7N + 5.3N + 7.4N is supposed to equal to zero. I tried to use the perdenicular components approach using 5.3N and 7.4N. 5.3 N: cos46=x/5.3 x=3.7 sin46=y/5.3 y=3.8 7.4 N: cos60=-x/7.4 x=-3.7 sin60=y/7.4 y=6.4 Sum of x= 3.7 + (-3.7) =0 Sum of y = 3.8+6.4 =10.2 Therefore, my 9.7N should be 10.2N? Then how do I prove the net force to be 0? So does that mean that my experiment was inaccurate?