Springs and Harmonics - MCAT Chemical and Physical Foundations of Biological Systems

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Question

A mass hanging in equilibrium is attached to a fixed surface on the ceiling by a spring. The mass is pulled down from the ceiling, then released and allowed to move in simple harmonic motion. The mass does not lose energy due to friction or air resistance. Which of the following would increase the frequency with which the mass moves through the equilibrium position?

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Answer

This problem focuses on understanding simple harmonic motion. The formula to identify the frequency, or cycles per second, that the mass moves is given below, where is the spring constant of the spring and is the mass of the object attached.

Notice that the frequency does not depend on how far the mass is displaced originally. If the mass is displaced more, it will simply be moving faster when it goes through the equilibrium position. It will not, however, move through the equilibrium position any more frequently than it would if it had been displaced less.

Increasing the mass of the object attached would increase the denominator in the formula, and would therefore decrease the frequency of the harmonic motion.

Increasing the spring constant, , would increase the numerator of the formula, which would result in an increase in the frequency on the motion. The spring constant is directly proportional to the stiffness of the spring; thus, increasing stiffness will increase frequency.

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