In other words, all sounds have a source. All sources of sound vibrate or shake back and forth. These vibrations move through the air to your ear and your brain tells you what the vibrations mean. For example, if your cat meows, she is the source of the vibrations making sound. You know the sound is a meow and not two dogs barking because the vibrations are different and your brain has learned the difference.
Sound sources can vibrate fast or slowly.
The speed of vibration can change. The speed of vibration is called frequency. The prongs can also change in the amount they vibrate or how far they move back and forth. If they move back and forth a large amount, the sound is loud. This amount of movement is called amplitude.