Hey all, I'm looking at an example in John Taylor's Classical Mechanics that I have some questions about. The example states: Consider a simple pendulum (mass m, length L) mounted inside a railroad car that is accelerating to the right with constant acceleration A. Find the angle at which the pendulum will remain at rest relative to the accelerating car and find the frequency of small oscillations about this equilibrium angle. First question: what small oscillations is he talking about? Does he mean the bob will oscillate about the angle? Or that it will oscillate in and out, effectively altering the angle slightly? He goes on to say that in the inertial reference frame, there are two forces, the tension and 'mg'. Net F = T + mg. In the noninertial frame we introduce the inertial force, -ma Net F = T + mg - mA. Setting g(eff) = g - A, the noninertial net force is F = T +mg(eff) Second question: He has an illustration of the car, with the pendulum inside swinging to the left, and a second illustration beside it of the triangle made by the pendulum. The hypotenuse is labeled as g(eff), the vertical side as 'g' and the bottom as '-A'. Why isn't the tension included on the hypotenuse? The figure has this caption: A pendulum is suspended from the roof of a railroad car that is accelerating with constant acceleration A. In the noninertial frame of the car, the acceleration manifests itself through the inertial force -mA, which in turn, is equivalent to the replacement of g by the effective g(eff) = g-A.