What do you feel as you hum?
How did you create different pitches?
There's a vein not too far from your vocal cords. Why do we hear air vibrating the vocal cords amplified, but not our blood pulsing through our veins?
What's making the sound and how do we hear it?
The teal window of the applet emulates what one would see if an oscilloscope were next to a keyboard. An oscilloscope is a tool physicists use to analyze the quality of sounds and many other kinds of waves. Because an oscilloscope shows the shape of a wave with a repeating pattern, some assume that what they see on the screen is the actual shape of the wave produced by the different notes, but this assumption is not correct. Instead, the oscilloscope shows a graph of the changing pressure of the sound wave. That is, sound is a compression wave, so it would not look like a sine wave or for that matter, a square, triangle, or sawtooth wave.
Think of another electronic tool you may have seen in the hospital or in a medical drama: the EKG or electrocardiogram. The graph seen on that screen is not a picture of the heartbeat, but a graphical representation of a heartbeat, one which health professionals use to get a snapshot of a patient's well-being. It is showing electrical pulses from the heart.
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