## Relative Velocity – Class 11 | Chapter – 3 | Physics Short Notes Series PDF for NEET & JEE

Relative Velocity: Relative velocity is the velocity of an object as observed from the point of view of another object. In other words, it is the velocity of an object relative to a particular frame of reference.

For example, imagine two cars driving on a straight road. From the perspective of the driver of the first car, the second car appears to be moving relative to the first car. However, from the perspective of a stationary observer on the side of the road, both cars are moving and the second car appears to be moving slower or faster depending on the direction it is moving relative to the observer.

## Formula of Relative Velocity

The relative velocity between two objects can be calculated using vector addition. The magnitude and direction of the relative velocity can be found by subtracting the velocity of one object from the velocity of the other. Mathematically, this can be expressed as:

vrel = v2 – v1

where vrel is the relative velocity between the two objects, v1 is the velocity of the first object, and v2 is the velocity of the second object.

## Importance of Relative Velocity

Relative velocity is an important concept in physics and engineering because it allows us to understand how objects move relative to each other, even if they are moving at different speeds or in different directions. Here are a few reasons why relative velocity is important:

• Understanding motion in different frames of reference: The relative velocity of an object is different when observed from different frames of reference. This is important in many fields, including astronomy, where we need to understand the motion of objects relative to the Earth’s frame of reference, and engineering, where we need to understand the motion of objects relative to moving platforms like airplanes and ships.
• Calculating collisions: In many situations, it’s important to understand how objects will collide with each other. By calculating the relative velocity between two objects, we can determine the speed and direction of the objects at the moment of collision, which is crucial information for safety and design considerations.
• Navigation: Navigation systems often rely on relative velocity to determine the position of objects. For example, a GPS system can use the relative velocity of a satellite to calculate the position of a receiver on Earth.
• Understanding fluid dynamics: In fluid dynamics, understanding the relative velocity between a fluid and an object moving through it is important for calculating forces like drag and lift.

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