Objects vibrating at small amplitudes move sinusoidally, one sine per frequency

Evidence

There is, however, a physical answer to this question, because of the way objects almost universally vibrate or oscillate, especially for low amplitudes of oscillation. They vibrate sinusoidally, as one or a combination of sine functions, one for each frequency of vibration. In chapter 8, on string vibrations, the sinusoid will rule; here we anticipate sinusoidal supremacy and develop some implications. — Eric J. Heller, Why You Hear What You Hear- An…, 251

Categorization

• DEFINE: Establishes why sinusoidal motion is the fundamental type: because physical objects universally vibrate that way at low amplitude.