1. The problem statement, all variables and given/known data Ok, this is not homework, just something that's been bugging me and my tutor is unavailable(as usual) to help me. Why does increasing the mass of a system lower its natural frequency, like adding a concrete block to a washing machine. Come to think of it, I'm not even too sure about what natural frequency is. I know that it's the frequency at which resonance occurs, if the driving frequency is equal to the natural frequency, but what determines the natural frequency? How to obtain it? 3. The attempt at a solution I figured out that adding a concrete block is not damping, since it becomes a part of the system in oscillation, and not an external resistive force. Therefore the addition of the block does not damp the oscillation, but it changes the system's natural frequency, but then I come back to the problem of how additional mass affects natural frequency.