This is a very basic question,I also attempt to learn more from it.Some additional info would also be of great help. A girl whose mass is 40kg is using a swing set.The diameter of the wire used for constructing the links of the chain is 5mm.Determine the average normal stress in the links at the bottom of the swing,assuming that the INERTIAL FORCES CAN BE NEGLECTED. Q.The question is regarding the INERTIAL FORCES.I have drawn the resolution of forces diagram(attached and I am not sure it's correct).Here,where does one include the inertial/pseudo forces in this accelerating frame of reference? Q.Is this inertial force- 'pseudo' in the sense that the sagging of the swing appears from a imaginative force taking the swing as the reference frame? Hope the questions are clear.Please view the attachment diagram.