1. The problem statement, all variables and given/known data A pendulum is constructed from a fixed length of light thread and and a spherical,low density,polystyrene bob.It is forced to oscillate at a different frequencies in air,and the response is shown in the graph below. 2. Relevant equations 3. The attempt at a solution This is the answer.I have googled it and still need explaination regarding how does ringing something at resonant frequency in vacuum causes the amplitude to tend to infinity. Thanks for your help!