How to Distinguish Velocity from Speed: Key Differences Explained
The unit of velocity can be defined as the ratio of unit of distance and unit of time. Students should not confuse velocity with speed as both are different from one another. Although the units of speed and velocity are similar, velocity, being a vector quantity, is defined as the rate at which an object changes its position with respect to a frame of time and reference.
The unit of velocity and speed is m/s, and the formula for average velocity is
\[V=\frac{s}{t}\],
where
S- The total displacement
t - The total time taken
Velocity is a physical quantity that is used to measure the speed along with the direction of an object. Velocity is one of the most important attributes of a moving object and the foundation of mechanics in the subject of physics. The equations of motion and along with calculating the time taken by a body to cover a particular distance have immense use of the concept of velocity.
Speed:
Speed is a scalar quantity and is defined as the rate of change of position of an object in any position and time.
The formula for speed is
\[S=\frac{d}{t}\] ,
where
s- The speed attained in m/s
d- The total distance travelled
t - The total time taken
Distance:
The length of the actual path traversed by the body during motion in a given interval of time is called the distance travelled by that body.
Distance is a scalar quantity and it can never be zero or negative during the motion of an object.
Displacement:
At a given interval of time, the displacement is defined as the shortest distance between the two positions of the body in a particular direction at that time and is given by the vector traced from the initial position to the final position.
Displacement is a vector quantity, i.e., it has both magnitude and direction. Therefore, in a given interval of time, it can be positive, zero, or negative.
SI Unit of Velocity
The velocity of the body is defined as the rate of change of displacement of the body with time. It is also defined as the speed of an object in a given direction. The relation is given by
Velocity is a vector quantity, i.e., it has both magnitude (speed) and direction.
The velocity depends upon the displacement of the object, which means that velocity can be zero, positive, or negative, according to its displacement as zero, positive, or negative.
SI unit or MKS (Meter-kilogram-second) unit of velocity is also meter per second or m/s or m s⁻¹, where m/s is the SI base unit of velocity.
Velocity Unit Symbol
The symbol for the unit of velocity is ms⁻¹ or m/s.
SI unit of Average Velocity
The average velocity of the object is defined as the total displacement of the object divided by the total time taken. It is given by
The SI unit of average velocity is m s-1 or m/s.
The dimensional formula for the same is given by M L T-1
CGS (centimeter-gram-second) unit for velocity is cm s⁻¹ .
The SI Unit of Speed
Speed of an object is defined as the rate of change of position of an object in any direction. It is given by
Speed is a scalar quantity. It gives no idea about the direction. However, the speed of the object can be positive, zero, or negative.
Angular Velocity Units
The angular velocity of an object in a circular motion is specified as the rate of change of its angular displacement. It is usually represented by the symbol omega (ω), given by
Angular displacement is a vector quantity. Its direction is the same as that of ΔӨ,
Where ΔӨ is the angular displacement and is defined as an angle made by an object moving around a circular path.
The SI unit of angular velocity is radians per second,
Where radian is a dimensionless quantity.
The SI unit of angular velocity is 1/ s or second⁻¹ or s⁻¹.
In S.I. base units: s⁻¹.
The dimensional formula for angular velocity:
M⁰L⁰T⁻¹
Angular Displacement Units
The angular displacement of the object moving around a circular path is defined as the angle made or traced by the radius vector at the axis of the circular path in a given time.
Such as the motion of a stone when tied to a string makes an angle Ө, where Ө is the angle swept by the stone.
Angular displacement is a vector quantity.
Unit of Velocity of Light
The velocity of light is a fundamental constant that corresponds to the speed of electromagnetic radiation in a vacuum and has a value approximately equal to 2.9979 x 10¹⁰ centimeters per second.
The unit of velocity of light is taken as the unit of velocity, i.e., SI or MKS unit is m/s and the CGS unit is cm/s.
Velocity Units
Miles per hour (mph)
Kilometers per hour (kmph)
Knot
Foot per second or ft /s or fps
Feet per minute or ft/ m or fpm
Foot per hour
Meter per hour
Inch per second
Kilometers per second (kps)
Centimeters per hour (cmph)
Meter per minute
Millimeter per minute (mmpm)
Mile per minute
Millimeter per second (mps)
Centimeter per minute
Speed of light
Benz (Bz)
FAQs on What is the Unit of Velocity in Physics?
1. What is the SI unit of velocity?
The SI unit of velocity is metres per second (m/s). This is the standard unit used in the International System of Units for scientific calculations, as per the CBSE curriculum. While other units like kilometres per hour (km/h) are used in daily life, m/s is the standard for physics problems to ensure consistency.
2. What is the fundamental difference between speed and velocity?
The key difference is that speed is a scalar quantity, while velocity is a vector quantity. This means:
- Speed describes only how fast an object is moving (e.g., 60 km/h).
- Velocity describes both the speed and the direction of motion (e.g., 60 km/h East).
Therefore, velocity provides a more complete description of an object's motion than speed does.
3. How is the unit of velocity derived from its formula?
The unit of velocity is derived directly from its definitional formula: Velocity = Displacement / Time. In the SI system, the standard unit for displacement is the metre (m) and the standard unit for time is the second (s). By dividing the unit of displacement by the unit of time, we get the resulting unit for velocity, which is metres per second (m/s).
4. Can velocity be negative? Explain with a real-world example.
Yes, velocity can be negative because it has direction. A negative sign typically indicates motion in the opposite direction to a pre-defined positive direction. For example, if a train moving north is said to have a positive velocity (+50 m/s), the same train moving south at the same speed would have a negative velocity (-50 m/s). The negative sign simply denotes the opposite direction.
5. What are the different types of velocity used in physics?
Velocity can be classified into four main types based on its characteristics:
- Uniform Velocity: When an object covers equal displacements in equal intervals of time. Both its speed and direction are constant.
- Variable Velocity: When an object's speed, direction, or both change over time.
- Average Velocity: The total displacement of an object divided by the total time taken. It represents the overall velocity over a period.
- Instantaneous Velocity: The specific velocity of an object at a particular moment in time.
6. Why is velocity considered a vector quantity while speed is a scalar?
Velocity is a vector because its calculation is based on displacement, which is itself a vector quantity (it has both magnitude and direction). Since velocity is displacement divided by time, it inherits this directional property. In contrast, speed is calculated using distance, which is a scalar quantity (it only has magnitude, representing the total path covered). Therefore, speed (distance/time) is also a scalar.
7. How does the concept of average velocity differ from instantaneous velocity?
Average velocity provides an overview of motion for an entire trip, while instantaneous velocity is a snapshot at a single moment. For example, if a car travels 120 km north in 2 hours, its average velocity is 60 km/h north. However, during the trip, its instantaneous velocity could have been 80 km/h at one moment and 40 km/h at another. The speedometer in a car shows instantaneous speed, not the average for the whole journey.
8. What is the importance of using a standard unit like m/s for velocity in physics?
Using a standard unit like metres per second (m/s) is crucial for maintaining consistency and universality in scientific work. When scientists and students worldwide use the same SI units, it eliminates ambiguity and ensures that experimental results can be easily compared and verified. It also allows for the correct application of physical formulas and constants (like g ≈ 9.8 m/s²) without requiring complex and error-prone unit conversions.
9. In what real-world scenarios is understanding the precise unit and direction of velocity critical?
Understanding the precise velocity is critical in many fields where direction is as important as speed. For example:
- Aviation: Pilots use velocity to calculate the effect of wind on their aircraft's path and arrival time. The wind's velocity must be factored in to determine the plane's actual ground-track.
- Weather Forecasting: Meteorologists track the velocity of hurricanes and storms to predict their path and point of landfall, which is essential for issuing timely public warnings.
- Space Exploration: The velocity of a rocket must be precisely controlled to enter a specific orbit around a planet or to land safely on its surface.
