15 • Oscillatory Motion - ECHSPhysics

Oscillations and
Mechanical Waves
W
e begin this new part of the text by studying a special type of motion called
periodic motion. This is a repeating motion of an object in which the object
continues to return to a given position after a fixed time interval. Familiar objects
that exhibit periodic motion include a pendulum and a beach ball floating on the
waves at a beach. The back and forth movements of such an object are called oscillations.
We will focus our attention on a special case of periodic motion called simple
harmonic motion. We shall find that all periodic motions can be modeled as
combinations of simple harmonic motions. Thus, simple harmonic motion forms a basic
building block for more complicated periodic motion.
Simple harmonic motion also forms the basis for our understanding of mechanical
waves. Sound waves, seismic waves, waves on stretched strings, and water
waves are all produced by some source of oscillation. As a sound wave travels
through the air, elements of the air oscillate back and forth; as a water wave travels
across a pond, elements of the water oscillate up and down and backward and forward.
In general, as waves travel through any medium, the elements of the medium
move in repetitive cycles. Therefore, the motion of the elements of the medium bears
a strong resemblance to the periodic motion of an oscillating pendulum or an object
attached to a spring.
To explain many other phenomena in nature, we must understand the concepts of
oscillations and waves. For instance, although skyscrapers and bridges appear to be
rigid, they actually oscillate, a fact that the architects and engineers who design and
build them must take into account. To understand how radio and television work, we
must understand the origin and nature of electromagnetic waves and how they propagate
through space. Finally, much of what scientists have learned about atomic
structure has come from information carried by waves. Therefore, we must first study
oscillations and waves if we are to understand the concepts and theories of atomic
physics. ■
Drops of water fall from a leaf into a pond. The disturbance caused by the falling water
causes the water surface to oscillate. These oscillations are associated with waves moving
away from the point at which the water fell. In Part 2 of the text, we will explore the principles
related to oscillations and waves. (Don Bonsey/Getty Images)
PART
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