• Background
• Instructions
• Illustration
• Quiz

## Background

Under normal conditions, at sea level, sound travels very fast, but much more slowly than light. Sound travels at about 344 m/s (761.2 mph). This is a bit faster than a civilian jet plane (a typical jet on its way from Chicago to New York travels at a peak speed of 550 mph). However, we have planes, mostly used by the military, that can equal and exceed the speed of sound. Indeed, the military has planes that exceed the speed of sound by as much as 3 times (“Mach 3” in military terms means 3 times the speed of sound). Such high speeds are avoided for typical civilian aircraft because they leave a tremendous wake collision of sound, called a sonic boom, behind them when the plane reaches and exceed the speed of sound. Interestingly, because the planes themselves are going faster than the sounds they make, pilots and passengers on such supersonic planes experience an incredibly quiet ride.

In this activity, you can watch how the movement of a sound source, like a plane, alters the sounds it emits as it travels slower, at, and faster than the speed of sound.

## Instructions

### Full Screen Mode

To see the illustration in full screen, which is recommended, press the Full Screen button, which appears at the top of the page.

### Settings

Below is a list of the ways that you can alter the illustration. The settings include the following:

Turn Sound On: start of stop the simulated sound represented by circles leaving the small dot representing the sound source.
Center Sound Source: When the sound is off clicking this button will return the dot to the center of the animation area.
Horizontal speed of Sound Source: the speed of the sound source in the horizontal dimension relative to the drawing width.
Vertical speed of Sound Source: the speed of the sound source in the vertical dimension relative to the drawing height.
Frequency of Sound: the frequency of the sound, shown by how fast the circles come off of the sound source. Remember the lower the frequency, the greater the wavelength so the farther apart the circles will be from each other.

### Reset

Pressing this button restores the settings to their default values.