You pick up an empty briefcase and let it swing to and fro at its natural frequency. If the case were filled with books, would the natural frequency be lower, greater, or the same as before?

Solution 5E The time period and frequency of oscillation of simple or compound pendulum depends only on the length of the pendulum. The time period formula for these pendulums is, l T = 2 g--------------------(1) [approximately] Here in the above formula, no mass term is there. As it is independent of the mass, so it does not matter whether the suitcase is empty or filled with books. The frequency of oscillation will be same as before, because the suitcase can be considered as a compound pendulum.