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# Average Velocity

## Displacement divided by time.

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The Bullet Drop

### The Bullet Drop

Credit: U.S. Army
Source: commons.wikipedia.org/wiki/File:5.56_M855A1_Enhanced_Performance_Round.jpg

The fundamental concept of breaking down motion into axial components has traditionally been taught by describing how a bullet dropped and a bullet fired simultaneously at same height along the horizontal plane would strike the ground at the same time. The scientists at MythBusters decided to test this concept. In the experiment, MythBusters used high-speed cameras to determine the exact moment when a bullet dropped and a bullet fired hit the ground.

• Watch the MythBusters Bullet Fired Dropped video below:

#### Why It Matters

• Many of the quantities that are described and investigated in physics have both a magnitude and a direction. These quantities include acceleration, velocity, force and momentum. When motion becomes too complex for the Cartesian coordinate system (x\begin{align*}x\end{align*},y\begin{align*}y\end{align*}, and z\begin{align*}z\end{align*}-axis), physicists can define different coordinate systems to help describe these motions.
• Once you can identify which axis an object is moving along or being acted upon, the steps needed to completely describe its motion become trivial. Explaining the world in the language of physics simply becomes a matter of describitng the motion for a given object in equations.

#### Can You Apply It?

Using the information provided above, answer the following questions.

1. In the MythBusters experiment shown in the video above, the time difference between the two bullets hitting the ground is approximately 40 milliseconds. Explain why the experiment was still considered a success.
2. Imagine a bullet with a mass 10 times larger than that of the MythBusters bullet. Would the experimental results be different? Explain.
3. What would the indications be if the bullet that was fired hit the ground significantly sooner than the bullet that was dropped? (Assume that it was not due to experimental error.)

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