Unit of Speed is meters per second or m/s. Speed is a physical quantity that measures the distance travelled by an entity per unit of time. The most commonly used units for speed are meters per second (m/s), kilometres per hour (km/h) and miles per hour (mph). Speed and Velocity are the same physical quantity except for the difference that velocity is a vector quantity and speed is a scalar quantity, so speed and velocity units are the same.
In this article, we will learn the definition of speed, the unit of speed, conversion between units in various systems, sample problems, and frequently asked questions related to the unit of speed.
Definition of Speed
The definition of speed is written as follows,
Speed is the rate of change of distance travelled by an object with respect to the time elapsed.
Speed Formula
Speed is calculated as the ratio of distance travelled to the time taken. Hence, formula of speed is given as
Speed = Distance/Time
What is Unit of Speed?
Unit of Speed is the measurement of magnitude of speed according to defined standard or convention. As the formula of speed is distance travelled per unit time, unit of speed would be the unit of distance per unit of time taken. For convenience, various systems of units have been adopted and units can be converted from one system to another by multiplication with some factor. The S.I. unit of speed is meters per second. The unit of speed depends upon the chosen units of distance and time.
Dimensional Formula for Speed
The dimensional formula for speed is [M0 L1 T-1]. It can be derived using the formula for speed, i.e. Speed = Distance/Time
Substituting the dimensions for distance and time, we get,
Dimension of Speed = [M0L1T0]/[M0L0T]
Dimension of Speed = [M0 L1 T-1]
SI Unit of Speed
S.I. unit of speed is meters per second abbreviated as m/s. It can be derived as follows:
- SI unit of distance = meter(m)
- SI unit of time = second(s)
We know that Speed = Distance/Time
Hence, SI unit of Speed = SI unit of Distance/SI unit of Time = meter/second = m/s = ms-1
Unit of Speed in Other Systems
The unit of speed in different systems is given as follows:
- MKS System: meters per second
- CGS System: centimeters per second
- FPS System: feet per second
What is 1 m/s?
1 m/s represents the speed in which an object covers 1 meter distance in 1 second.
Conversion between Unit of Speed in different Systems
The unit of speed can be converted from one system to another using following relations:
- 1 kilometer per hour = 5/18 meters per second
- 1 centimeter per second = 1/100 meters per second
- 1 foot per second = 0.3048 meters per second
- 1 mile per hour = 0.44704 meters per second
Using the above conversion system we can convert speed of unit from one form to other form
Convert km/h to m/s
To convert km/h to m/s we multiply by 5/18
(km/h) × 5/18 = m/s
For example, convert 60 km/h in m/s
Solution: 60 × 5/18 = 16.66 m/s
Convert m/s to km/h
To convert m/s to km/h we multiply by 18/5
(m/s) × 18/5 = km/h
For example, convert 16.66 m/s in km/h
Solution: 16.66 × 18/5 = 59.976 k/hr approximately equal to 60 km/h
How to Convert SI unit of speed to CGS Unit of speed?
The SI unit of Speed is meters per second and CGS unit of speed is centimeters per second. The conversion can be done as follows:
1 meter = 100 centimeters
1 meter/ 1 sec = 100 centimeters/ 1 sec
or, 1 m/s = 100 cm/s
For example, a speed of 5 m/s in SI units would be 500 cm/s in CGS units.
Facts about Speed
Some facts about speed are listed as follows:
- Speed can never be negative.
- Speed is a scalar quantity which means it has only magnitude but not direction.
- Speed of light in vacuum is 299,792,458 m/s.
- Speed of sound in dry air is 343.2 m/s.
- Escape velocity of earth, i.e. speed required to escape an object from the gravitational pull is 11.2 km/s.
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Solved Examples on Unit of Speed
Example 1: The distance travelled by a body is 3 kms in 10 mins. Find its speed in SI units.
Solution:
The SI unit for speed is m/s.
Distance Travelled = 3 kms = 3 × 1000 meters = 3000 m
Time Taken = 10 mins = 10 × 60 secs = 600 s
Now, Speed = Distance/Time
⇒ Speed = 3000/600 = 5 m/s
Thus, speed in SI units for given case is 5 m/s.
Example 2: Which of the following is a unit of speed?
(a) mm × s (b) sec/m (c) cm/s (d) mins/m
Solution:
We know that,
Formula for speed is distance/time.
Thus, Option (c) is correct.
Example 3: A body travels 45 seconds with a speed of 4 m/s and 30 seconds with a speed of 5 m/s. Find the average speed for this journey.
Solution:
We know that,
Average Speed = (Total Distance Covered)/(Total Time Taken)
Here, Total time taken = (45 +30) s = 75 s
Distance travelled in first 45 seconds = 4 × 45 = 180 m
Distance travelled in later 30 seconds = 5 × 30 = 150 m
Total distance covered = 180+150 = 330 m
Average Speed = 330/75 = 4.4 m/s
Practice Questions on Unit of Speed
Q1. Calculate speed of a body which travelled 300 meters in 5 mins.
Q2. Convert the speed 5 km/h into SI units.
Q3. A car is travelling at the speed of 40 km/h. Find its speed in miles per hour.
Q4. A body travels first half of its journey with a speed of 30 m/s and second half of its journey with 40 m/s. Find its average speed.
Q5. A man runs on a circular track having radius of 70 m covering a complete round in 1 minute. Find his speed in SI units.
FAQs on Unit of Speed
What is SI unit of Speed?
The SI unit of speed is meters per second abbreviated as m/s.
What is meant by average speed?
Average speed is the ratio of total distance covered by an object and time taken for it.
Is Speed a scalar or vector quantity?
Speed is a scalar quantity, i.e. it possess magnitude only but not direction.
What are the commonly used units of speed?
The commonly used units of speed are meters per second (m/s), kilometers per hour (km/h), miles per hour (mph), and feet per second (ft/s).
Are units of speed and velocity same?
Yes, units of speed and velocity are same as units of distance and displacement are the same.
How do you convert km/h to m/s?
To convert km/h to m/s multiply the magnitude given in km/h with 5/18