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Motion and its Applications

Distance, Displacement, Speed, Velocity 

Displacement is defined as the distance traveled in one direction. 

 The symbol for displacement is  .

 Displacement is  a vector quantity.   A vector has both magnitude (size) and direction.

The standard SI unit of displacement is the meter (m). 

The symbol for distance is d.
(note that there is no arrow on top of the letter d.  This means that it is a scalar quantity - distance has just magnitude but no direction).

Velocity is the speed an object travels in one particular direction. 

 The symbol for speed is v and the units for speed are " meters per second" or (m/s). 

 The symbol for velocity is 
 (Velocity is a vector, Speed V  is a scalar - note that the letter v has no arrow when it symbolizes speed)

To calculate the average speed of an object we use the following equation:  

In the equation, v=d/t, d is the total distance traveled by an object, and t is the total time taken for an object to travel that distance.
Note: Use the "triangle method" as a quick way to rearrange the equation. 

Help Video:

A Bit About Units:

• The standard metric  unit for distance is the meter - the symbol for metro is m
• The standard metric  unit for time is the second - the symbol for second is s
• The standard metric  unit for speed is the metre/second - the symbol for speed is m/s
• Longer distances are measured in kilometers - the symbol for kilometer is Km
• Longer times are measured in hours - the symbol for hours is h

When you solve a problem or answer a question always give your answer in standard units.

Sample Problem:

You take your dog for a walk at 30 cm/s.  How much will you have walked in 20 minutes?

Solution:

Given:  v = 30 cm/s = 0.30 m/s
            t = 20 min. = 20 min X 60 s/min = 1200 s

Find: d

Therefore    d = 0.30 m/s  X 1200 s  = 360 m

Therefore you would have walked a distance of 360 m

  

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