Difference Between Speed and Velocity

Speed and velocity are the terms used to describe the motion of objects. However, the two terms are not similar. Speed is a scalar quantity that describes the rate at which an object moves. In other words, speed is the distance travelled by an object per unit time. Velocity, on the other hand, is a vector quantity. It can be defined as the rate at which a moving object changes its position. It includes both the magnitude and direction of a moving object.

Speed and velocity of an object are calculated using different formulas. While speed consider the distance covered by an object in a given time, velocity measures the displacement of the object per unit time. 

Read More: Speed, Distance and Time Formula

Key Terms: Speed and Velocity, Acceleration, Average Speed, Average Velocity, Displacement, Instantaneous Speed, Terminal Velocity

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What is Speed?

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Speed is the distance covered by an object in a specific period of time. It is independent of the direction in which the object is moving. To calculate the speed of an object, we need to divide the total distance travelled by the object with the given time. The SI unit of speed is m/s. 

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

Using this formula, the dimensional formula of speed can also be derived;

Dimensional formula of distance = M⁰L¹T⁰ 

Dimensional formula of time = M⁰L⁰T¹

therefore, the dimensional formula of speed = \(\frac{M^{0}L^{1}T^{0}}{M^{0}L^{0}T^{1}}\)= M⁰L¹T^-1. 

Types of Speed

Speed can be divided into four types given below:

• Uniform Speed – When an object travels equal distance in equal interval of time, it is said to have uniform speed. 
• Variable Speed – It is the speed in which an object cover unequal distances in equal interval of time. In this, the distance travelled varies, but the time interval remains consistent.
• Average Speed – It is the ratio of the total distance travelled by an object to the total time taken. 
• Instantaneous Speed – When an object is moving with variable speed, then its speed at any instant of time is called instantaneous speed. 

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What is Velocity?

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The rate of displacement of an object with respect to time is known as velocity. It is directly proportional to the displacement and inversely proportional to time travelled. It is a vector quantity that considers both magnitude and direction of the moving object. The SI unit of velocity is ms^-1. 

\(Velocity = \frac{Displacement}{Time}\)

When a moving object changes its direction or magnitude of velocity, then it is said to be accelerating. There are two velocities for an object in motion – initial velocity and final velocity.

• Initial velocity is the velocity with which an object started moving, whereas, final velocity is calculated when the object has reached its maximum acceleration.
• The initial and final velocities of a moving object are denoted by ‘u’ and ‘v’ respectively. 

Read More: Difference Between Acceleration and Velocity

Types of Velocity

There are 4 types of velocity as mentioned below: 

• Constant Velocity – When an object undergoes equal displacement in equal interval of time, it is said to have constant velocity. 
• Variable Velocity – Variable velocity is the velocity in which the magnitude and direction of the object keeps changing with respect to time. 
• Instantaneos Velocity – The velocity of an object at any instant of time is called as instantaneous velocity. 
• Terminal Velocity – The highest velocity attained by an object as it falls through a fluid is the terminal velocity.

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Difference Between Speed and Velocity

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The table below contain the key differences between speed and velocity:

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Formula for Calculating Speed and Velocity

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The formula for calculating speed and velocity of a moving object are provided below: 

Speed

The formula for speed is given by, Speed = Distance ÷ Time

s = d ÷ t

where;

• s = speed
• d = distance travelled
• t = time taken to cover the distance d

Velocity

The velocity of an object can be calculated using the formula, Velocity = Displacement ÷ Time

v = \(\triangle\)s ÷ \(\triangle\)t

where;

• ​\(\triangle\)s = change in position
• Change in position = Final Position – Initial Position
• \(\triangle\)t = time 

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Things to Remember

• Speed and velocity are used to find the rate at which an object is moving. 
• Speed is the distance covered by an object in a given interval of time, whereas velocity is the rate at which an object changes its position with respect to the time.
• Speed is a scalar quantity but velocity is a vector quantity. 
• The speed of an object can never be negative or zero. However, the velocity of an object can be positive, negative and zero. 
• Both the speed and the velocity are measured in ms^-1.