Unit Of Speed: SI Unit, Derivation, And Conversion - Collegedunia

What is Speed?

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Speed is the rate of change of position of an object moving in any direction.

• Speed is the ratio of the distance covered by an object to the time in which the distance was covered.
• It is a scalar quantity, with only magnitude and no associated direction.

Dimensional Analysis Video Explanation

Speed is the measurement of how fast an object moves to cover a distance.

• Speed can not have a negative value.
• The dimensional formula of Speed is M0.L1.T-1
• It is denoted by the symbol v and is measured in the units of meters per second (m/s).

Interesting Facts about Speed Galileo Galilei, a great Italian astronomer was the first to estimate speed by calculating distance over time. Earth's typical orbital speed is around 30 km/s. Earth's surface moves at a rate of around 460 m/s at the equator which is equal to a speed of around 1,000 miles per hour. In a vacuum, the speed of light is approximately 299,792 kilometers per second (186,282 miles per second). In the air, the speed of sound is approximately 343 m/s, or 767 mph, or 1235 km/h.

SI Unit of Speed

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SI Units are the standard units of measurement that are uniform throughout the world to avoid confusion. SI units of any physical quantity are laid out by the International System of Units (SI).

The SI Unit of Speed is Meters per Second (m/s).

• This standard unit of speed signifies how many meters an object can travel within a second.
• For instance, if an object travels 10 meters in a second, then, the speed of the object will be 10 m/s.

The SI unit of speed is derived from the standard units of Distance (meters) and Time (seconds). It can be understood as follows:

\(Unit \hspace{1mm} of\hspace{1mm} Speed = \frac{Unit\hspace{1mm} of \hspace{1mm}Distance}{Unit \hspace{1mm}of \hspace{1mm}Time} = {m\over s}\)

Read More:

Relevant Concepts
Unit of Force	Unit of Acceleration	Unit of Velocity
Unit of Momentum	Unit of Mass	Unit of Volume
Unit of Length	Unit of Electricity	Unit of Weight

Other Units of Speed

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Speed can be measured in various other units apart from its SI unit. In certain cases such as measuring a vehicle's speed, it is more sensible to use hours instead of seconds. Thus, kilometers per hour (kmph) or miles per hour are used to measure the speed of vehicles.

The different systems of measurement of speed are:

• CGS Unit of Speed: In the CGS system of units, length is measured in terms of centimeters and time in terms of seconds. Therefore we can derive the unit of speed as centimeters per second or cm/s.
• FPS Unit of Speed: FPS Units belong to the category of imperial units. Here, length is measured in terms of foot and time in terms of the second. Therefore, the unit of speed can be expressed as a foot per second or ft/s.

Read More: Difference Between Speed and Velocity

Conversion of Units of Speed

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The unit conversion of the different units of speed from CGS to SI system and vice versa can be done with the help of the given table:

Units	Conversion
Km to Cm	1 km = 100000 cm
Km to M	1 km = 1000m
Cm to m	1 cm = 0.01m
M to mm	1 m = 1000 mm
Cm to mm	1cm = 10 mm
Hour to min	1 h = 60 min
Min to sec	1 min = 60 sec

Speed Formula

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Speed is the ratio of the distance covered by an object to the time taken to cover that distance. Speed can be calculated using the given formula:

\(Speed = {Distance \over Time}\)

Using the appropriate symbols for all the physical quantities, the Speed Formula is expressed as: 

\(v = {d \over t}\)

Where

• d is the Distance covered by an object measured in meters (m).
• t is the time taken to cover the distance measured in seconds (s).
• v denotes the Speed of an Object measured in m/s.

Speed, Distance, and Time Formula

Solved Example Example: A train covers a distance of 120 km in an hour. What will be the speed of the train in m/s? Solution: It is given that Distance covered by Train = 120 km = 120 × 1000m = 120000m  Time Taken by Train = 1 hour = 60 × 60 = 3600 second Using the Speed Formula, Speed = Distance/Time Speed of Train = 120000/3600 = 33.3m/sec Thus, the speed of the train is 33.3 m/s.

Also Check:

Related Topics
Standard Measurement Units	System of Units	Fundamental and Derived Units of Measurements
Speed, Distance, and Time Formula	Relative Speed	Average Speed Formula

Things to Remember 

• Speed is the rate at which an object travels over a certain distance.
• Speed is a scalar quantity with only direction and no magnitude.
• It is measured in terms of distance divided by time.
• Speed Formula is given as Speed = Distance/Time.
• The SI unit of Speed is meters per second (m/s).
• The CGS unit of speed is centimeters per second (cm/s).
• The FPS unit of speed is foot per second (ft/s).
• The speed of vehicles is always measured in terms of Kilometers per hour (kmph) or miles per hour (mph).

Previous Years’ Questions

1. A block of mass of 1 kg is moving on the x-axis… [UPSEE 2017]
2. If a body moves for 2 s with 15 m/s velocities towards the east and then moves… [JCECE 2006]
3. A packet is dropped from a flight ascending with a velocity at a height of… [KEAM 2013]
4. The position x of a particle with respect to time t along… [NEET 2007]
5. The apparent frequency observed by a moving observer away from… [KEAM]
6. The variation of speed (in m/s) of an object with time… [KEAM]
7. The linear momentum p of a body varies with time and it is given by… 
8. The velocity of an object moving in a straight line path is given as… 
9. A child is swinging a swing. Minimum and maximum heights of swing from… [JCECE 2004]
10. Hie equation of motion of a panicle is given by… [TS EAMCET 2018]
11. The nature of a graph drawn for a freely falling body with time on… [TS EAMCET 2019]
12. A body moving with uniform acceleration describes 40 m in the first… [COMEDK UGET 2004]
13. The displacement time graph for two bodies A and B are straight lines… [COMEDK UGET 2004]
14. What will be the ratio of speed in the first two seconds to the speed in the next… 
15. If a person sitting in a train moving with a constant velocity along a straight line…