Speed and Velocity

Speed and Velocity

Speed and Velocity

Speed

Speed can be defined as the time that any moving object needs in order to cover a specific distance. That means, high speed requires covering large distance in a short time. Also, low speed requires covering the same distance in a long time. The speed may be zero in the case of no-movement of the object. It’s a scalar quantity that does not need a direction to be described.  

The speed of any object may be changed during the movement so, speed is determined either by average speed, which is calculated for the whole movement journey, or by instantaneous speed, which is calculated for any given point at a specific time during the journey.

Velocity

Velocity needs both scale and direction to be completely described as it’s a vector quantity. The position of the object is changed during the movement and the rate of the changes is known as the velocity. If the speed of a moving object is 100 km / hr then, its velocity may be 100 km / hr West or East or any direction.

Velocity vector direction of any moving object can be described easily by knowing the direction of motion as it will be the same. For example, if the car is moving rightwards with a speed of 120 km per hr then, its velocity will be 120 km per hr, rightwards. The direction is important in the case of describing velocity.

Speed & Velocity Calculations

In order to calculate the speed and velocity of any moving object, the average quantity of whole motion trip is calculated. The calculations of speed and velocity can be done as follows:

Average speed calculation formula:

Average Speed = Distance Travelled / Time of Travel

Average Velocity calculation formula:

Average Velocity = ∆ Position / Time = Displacement / Time

Speed & Velocity Units

According to the International System of Units (SI), speed units are taken as follows:

Km / hr. or m / sec.

Where,

     -        Km: kilometre.

     -        hr: Hour.

     -        m: Meter.

     -        sec: Second.

According to the English system, speed units are taken as follows:

ft / hr. or ft / sec.

Where,

     -        ft: Foot.

     -        hr: Hour.

     -        sec: Second.

The units of velocity are similar to that of speed but, in the case of velocity, the unit will be followed by the direction of motion; East, West, North, South, rightwards… etc. 

Speed and Velocity Examples

  §  Calculate the Average speed and velocity of the man moving 90m to the north, and 72m to the south in 54 seconds.

Answer

Total distance covered by the man = 90 + 72 = 162 m

Average Speed = distance travelled/time of travel = 162 / 54 = 3 m/s

Average Velocity = displacement/time = (90 - 72) m / 54 s = 18 / 54 = 0,33 m/s, North.

  §  Calculate the speed and velocity of the car moving 90 km rightwards in 2 hours.

Answer

Speed = Distance / Time = 90 / 2 = 45 km/hr.

Velocity = Displacement / Time = 90 / 2 = 45 km/hr, rightwards.