Editing Doppler Ball (section)

===Full Explanation===

Sound is a wave that travels through a medium (solid, liquid, or gas) by a series of compressions. Since the compression waves occur at a variety of regular time intervals, we can perceive a variety of frequencies, or "pitches" of sound. The human ear can hear from about 20Hz to about 20,000Hz or 20 compression waves per second to 20,000 compression waves per second! When an object is moving and emitting sound, the distance between the compression waves can change, resulting in a change of what pitch we hear. This change in pitch is what we call the '''''Doppler Effect''''', and we can calculate the change by use of the following equation:

{| class="wikitable" style="color:black; background-color:#ddd; text-align: center; margin: auto"
| Frequency heard (receiver), '''f''' =
| [('''v + v<sub>r</sub>''') / ('''v + v<sub>s</sub>''')] * '''f<sub>0</sub>'''
|-
| Frequency heard (thrower), '''f''' =
| [('''v + v<sub>s</sub>''') / ('''v + v<sub>r</sub>''')] * '''f<sub>0</sub>'''
|}

In this equation, '''v''' is the speed of sound, '''v<sub>r</sub>''' is the velocity of the ball moving towards the receiver, '''v<sub>s</sub>''' is the velocity of the ball moving towards the thrower, and '''f<sub>0</sub>''' is the original frequency. Since the thrower is, well, throwing the ball to the receiver, the '''v<sub>r</sub>''' value will be positive, while the '''v<sub>s</sub>''' value will be negative. This means that in the first equation, we will have a multiplication factor greater than 1.0, resulting in an increased frequency. Likewise, the second equation will have a multiplication factor of less than 1.0, resulting in a decreased frequency.

This effect applies to all types of waves, including light waves, and is a known pheonomena in Astronomy called the '''''Redshift/Blueshift Effect'''''. If astronomers are observing a distant object, such as a star, they will make calculations based on their observations to determine the mass, direction of movement, and color of the star. However, they sometimes will look at a star and find that, instead of it looking yellow, it might look red. This tells the scientist that the star must be moving ''away'' from us, and they can calculate the speed of the star by using what they know (it should be yellow) and what they see (it looks red). Likewise, the opposite can happen where the star might look blue instead, meaning that it is moving towards us. They can then calculate using what they know (it should be yellow) and what they see (it looks blue) to determine how fast the star is moving.