Every mode of an object’s vibration is itself a sinusoid

Evidence

A key point, not yet obvious from what we have said so far, is that most objects can vibrate in many ways, even thousands or millions of ways, and yet each of these individual ways is itself a sinusoidal oscillation, in that any point on the object is moving up and down, or side to side, and so on, sinusoidally. Hardly a more important principle can be expressed in all of the subject of acoustics, but we shall have plenty of opportunities to point it out again- for example, in the next section. — Eric J. Heller, Why You Hear What You Hear- An…, 296

Categorization

• DEFINE: Clarifies that each of many possible vibration modes of an object is individually sinusoidal.