A U-shaped fork of steel first invented in 1711 by trumpet player John Shore, the tuning fork is a tool produces a specific note that helps musicians keep their instruments in tune. They also are a great conversation starter about forced vibration, resonance, pitch, and frequency. From HowStuffWorks.com:
Every time you strike a tuning fork, you’re setting off a tiny, invisible hurricane. Thrashing back and forth at tremendous speeds, the two prongs of the fork, known as “tines,” are smashing against nearby air molecules, kicking off a chain of impacts that echo through the air. When these violent, microscopic collisions hit your eardrum, your brain processes them as a gentle hum.
Two identical tuning forks and sounding boxes are placed next to one another. Striking one tuning fork will cause the other to resonate at the same frequency. When a weight is attached to one tuning fork, they are no longer identical. Thus, one will not cause the other to resonate. When two different tuning forks are struck at the same time, the interference of their pitches produces beats.
Here’s another example of forced vibration and resonance — “the reinforcement or prolongation of sound by reflection from a surface or by the synchronous vibration of a neighbouring object” — from The Physics Classroom:
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