1. The problem statement, all variables and given/known data A mass of 2kg is sitting on a dial scale balance on the floor of a lift. What is the reading on the balance when the lift is moving downward with acceleration of 3 m/s2 2. Relevant equations F = ma F = mg where g = 10 m/s2 in this question. 3. The attempt at a solution Consider the mass first. Mass = 2kg and under gravity, the force is F = mg = 20N. Consider the reading on the scale, let's say x. Under gravity, F = mg = 10xN. It is given that the lift is accelerating downwards at 3 m/s2 and let's establish that moving downwards is negative. Using F = ma, we get F = ma = -6N. Since the scale and the mass are experiencing a net downwards force, we equate them to -6N. This is where I get stuck. The solutions give the equation: 10x - 20 = -6. Firstly, why is there a negative sign on the left hand side? Shouldn't it be positive since both objects are experiencing a downwards motion? And why does 10x go first as opposed to 20 being first? I'm not understanding the logic behind the left hand side. Thanks to those who answer!