# What is Velocity?

## By Joan Whetzel

Velocity, a word used frequently in scientific writing, relates to speed and motion. The fields of physics and astronomy makes use of velocity in many studies and experiments. Even sports analysis sometimes makes use of velocity, as in measuring the velocity of baseball's trajectory. It aids in the understanding of how the world - and the universe - works.

**Velocity Defined**

Velocity is defined as the speed of motion, that describes a body's speed and direction of motion. It is the rate at which an action occurs in a specific direction. Speed, by itself, is simply a measurement of how long it takes something to occur, the rate of motion or in the change of position. Speed is a scalar quantity, measuring distance and time, and is expressed as distance moved (d) per unit of time (t) Speed measurements don't take direction into account. Velocity, by comparison, measures the rage of change in an object's position, specifying its speed *and* direction of motion at each point in time. Where speed will say that an object moves 5 miles per second, velocity specifies that the object moves 5 miles per second east.

**Measuring Velocity**

Velocity (v) measurements (given in meters per second or kilometers / miles per hour) are found the same way as speed measurements. The distance traveled (s) is divided by the time it took (t). The velocity equation reads like this: v = s/t. An example of a velocity measurement might read: 70 kph/40mph northward. Positive and negative values in the measurement indicate movement in opposite directions, meaning the object changed directions and is now going in a direction opposite to its original path of motion. These values are displayed either on velocity-time graph (showing a path of continued motion that keeps changing direction while in motion) or a displacement-time graph (indicating movement from a fixed motion). Constant velocity calculations measure an object moving at a constant speed in a constant direction (the object moves along a straight path). When an object changes speed, direction, or both, then it changes velocity in what is called an acceleration.

Speed and Velocity equations:

Speed = Distance Traveled / Time of Travel

Velocity = A Position / Time = Displacement / Time

**Average Human Velocity**

Humans have been clocked doing various activities, and their average speeds averaged.

Humans:

a. walk at an average 3 miles per hour (5kph or 1.39meters/second).

b. jog long distance at an average 6 mph (10 kph or 2.7 m/s).

c. bicycle at an average 12 mph (20 kph or 5.56 m/s).

By comparison cars travel at an average 65 mph (104 kph or 5.56 m/s). Airplanes (specifically 7474s) travel at an average of 565 mph (910 kph or 252.57 m/s)

**Converting Speed and Velocity Measurements Between km/h and mph**

To convert from miles per hour (mph), the basic equations are as follows: 1 mph = 1.61 kph or 0.447 m/s. So the mph measurement is multiplied by kilometers per hour (kph) or by meters per second (m/s) to find the kph or m/s measurement.

Examples: 23 mph x 1.61 kph = 14.28 kph

23 mph x 0.447 m/s = 10.28 m/s

The conversions from kph and m/s work in the same manner.

Examples: 23 kph x 0.277 m/s = 6.37 m/x

23 kph x 0.621 mph = 14.28 mph

Examples : 23 m/s x 3.6 kph = 26.6 kph

23 m/s x 2.237 mph = 51.45 mph

**Where Velocity Measurements Are Used**

· Baseball and other sports - tennis, speed skating, speed cycling

· Wind - aeronautics and meteorology

· River water motion

· Traffic, airplanes, boats

· Rockets and space ships

· Projectiles like bombs and bullets

· Particle physics

· Light

· Falling objects

· Planet motion

· Water flow in pipes and sewers

· amusement park rides

**Resources**

Convert Units. *Convert km/h to mph.*

http://www.convertunits.com/from/kph/to/mph

Calculator Converter. *mph to km/h converter.*

http://calculator-converter.com/converter_mph_per_miles-hour_to_km-hour_calculator.php

American Heritage Dictionary. *Velocity.*

http://education.yahoo.com/reference/dictionary/entry/velocity

Math and Science Activity Center. *What Is Acceleration?*

http://www.edinformatics.com/math_science/acceleration.htm

Encyclopedia.com *Velocity.*

http://www.encyclopedia.com/topic/velocity.aspx

Wikipedia. *Velocity.*

http://en.wikipedia.org/wiki/Velocity

Physics Formulas. *Velocity Formula.*

http://www.physics-formulas.com/Velocity_Formula.html

The Physics Classroom. *Speed and Velocity.*

## Measuring Motion Velocity

## Measuring Velocity with a Motion Sensor

## Velocity

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