Hi all, I'm new to the forum and figured someone on here would be able to help me out w/ my question. I'm having trouble understanding something regarding an accelerometer. Here's a brief description of an accelerometer taken from an excerpt I read to get you all up to speed on what I'm dealing with: "An accelerometer is a device that may be used to measure the acceleration of an object moving horizontally. One type of accelerometer consists of a simple pendulum made up of a small dense body suspended from a "massless" rod. The unweighted end of the rod is fixed, but is allowed to pivot freely. When the system is accelerated to the right, the pendulum swings back toward the left, and makes an angle θ with the vertical. The size of this angle θ gives a measure of the acceleration, so the larger the angle, the greater the acceleration. When there is no displacement from the vertical, the system is traveling with a constant velocity." So my question has to do with the maximum angle that can be reached by the pendulum in the accelerometer. "Assuming there are no limitations on the acceleration of the object, the maximum angle(theta) that the pendulum of the accelerometer can make with the vertical has to be just under 90". The explanation that I read said that the vertical component of the tension in the rod needs to cancel out the mass of the bob, and in order to do so, the maximum angle would have to be less than 90 in order for there to be a vertical component of the tension. Now I understand the reasoning that was given, but I don't understand the logic behind it. I don't understand why the the tension in the string has to cancel out the mass of the bob and why it can't continue upwards past 90 degrees. Why can't there be a net force in the upward direction that would justify a greater angle? Any ideas? Thanks in advance for any help.