Learning Objectives
By the end of this activity, students will be able to:
Describe the relationship between sound and vibrations.
Observe how vibrations of a tuning fork create sound waves.
Demonstrate how vibrations can be transmitted into other media, such as water.
Relate tuning fork vibrations to ultrasonic testing methods in NDT.
Key Concepts
A tuning fork is an all-metal device that has a handle and two prongs, known as tines. When you strike it against a soft surface—like the bottom of a shoe or the palm of your hand—the tines vibrate back and forth several hundred times per second. The vibrations are usually so fast that you can only see it in slow motion.
The tuning fork’s vibrations interact with the surrounding air to create sound. As the tines move back and forth at tremendous speeds, the vibrations press air molecules together (forming compressions) and force them apart (forming rarefactions).
Together, a collection of compressions and rarefactions form a sound wave. Once a sound wave enters your ear canal and vibrates your eardrum, your brain interprets the vibrations as sound.
In ultrasonic testing, different types of sound waves are better suited to different materials, or to find specific types of discontinuities. The higher the frequency, the smaller the discontinuities that can be found; but, by increasing the sensitivity, penetration ability is decreased, meaning the sound waves cannot travel as deeply into a material to find discontinuities.
