Into the Swing of Things
An animation of "Newton's Cradle," showing the transfer of energy and an example of periodic motion.Copyright 2007 Dominique Toussaint, Wikimedia Commons http://commons.wikimedia.org/wiki/File:Newtons_cradle_animation_new.gif
After watching a 1940 film clip of the "Galloping Gertie" bridge collapse and a teacher demo with a simple pendulum, student groups discuss and then research the idea of motion that repeats itself—specifically the concepts of periodic and harmonic motion. They become aware of where and how these types of motion occur and affect them in everyday applications, both natural (seasons, tides, waves) and engineered (swings, clocks, mechanical systems). They learn the basic properties of this type of motion (period, amplitude, frequency) and how the rearrangement of the simple pendulum equation can be used to solve for gravitational acceleration, pendulum length and gravity. At lesson end, students are ready to conduct the associated activity during which they conduct experiments that utilize swinging Android® devices as pendulums.
Engineers are constantly exploiting the periodic nature of systems for technological use and ways to improve our lives. Mechanical engineers design machines that have periodic features. Music is created by manipulating sound waves, which are periodic. Manipulating both sound and electromagnetic waves creates communication. When engineers design bridges that span distances, the forces acting on the span must be considered so that periodic motion does not develop and cause structural failure. Periodic motion can be both helpful and harmful, depending on the situation.
After this lesson, students should be able to:
- List the properties of harmonic motion.
- Cite real-world examples of periodic motion.
- Explain how engineers utilize or harness periodic motion.