| Intermediate Technology Education | Energy and Power Technology | Pre-Design | Topic 3 | Activity 4 |

Speed and Velocity

To define speed and velocity and differentiate between the two.
  • Define speed
  • Define velocity
  • Investigate applications of speed and velocity in technological problems and solutions

Speed

Speed is the rate of motion.  In effect, it is the distance an object travels in a unit of time.  For example

Speed Distance Traveled Unit of Time
100 miles/hour 100 miles 1 hour
10 meters/sec 10 meters 1 second
50,000 kilometers/year 50,000 kilometers 1 year

As you can see from the table, speed can be described in any units of distance and time.  Mathematically, speed is described as

S = d / t

Speed  = distance traveled divided by time

For example, if you travel 200 kilometers in 4 hours, your (average) speed is

S = 200 km / 4 hr

S = 40 km/hr

which is usually written as

S = 40 k/h

Speed can be in any direction.  For example, if you travel along a highway at a fixed speed of 100 kilometers/hour, you may notice that the highway twists and turns, and over long distances you may actually travel north, east, south and west.  The next image illustrates this.

Speed

Figure Speed of a vehicle along a roadway

Suppose that the distance along the road from starting point to destination is 100 kilometers.  At a speed of 100 k/h, it will take 1 hour to travel the distance.  If you look at the map, it is obvious that the road does not travel in a straight line from start to destination.  If you could go it a straight line, the distance would be much less than along the roadway. 

Velocity

The next image shows the path you would take if you travelled in a straight line from start to destination.  In this case, the distance would be 60 kilometers. 

Velocity

Figure Velocity is the direct distance travelled (displacement) in a unit of time

As the image shows, after an hour of travelling at 100 kilometers per hour, you have driven 100 kilometers, but you are actually only 60 kilometers in a straight line from where you started.  We call this distance your displacement. 

Velocity is displacement per unit of time.  Velocity is speed and direction.  Velocity is measured in meters per second

In the previous 2 images,

  • Your speed was 100 k/h, and you could be travelling in any direction
  • Your displacement was 60 kilometers in 1 hour, in a straight line from start to destination.  Velocity was

V = (60 X 1000) meters / (1 hour X 60 minutes X 60 seconds)

V = 60000 / 3600

V = 16.67 m/s  (meters per second)

Velocity is stated in meters per second.

More Information

For more information check these pages

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