Physics is filled with fascinating concepts that help us make sense of the world around us. One such concept that plays a crucial role in our understanding of motion is “relative velocity.” This concept is the key to understanding how objects move in relation to each other, and it has applications in various fields, from everyday life to advanced engineering. In this blog, we’ll take a deep dive into the world of relative velocity, unravel its mysteries, and explore real-life examples to illustrate its significance.

What is Relative Velocity?

Relative velocity, in simple terms, refers to the velocity of an object as observed from another object’s perspective. It’s the rate at which one object moves concerning another, and it depends on the observer’s frame of reference. Think of it as seeing the motion of one object from the viewpoint of another.

Understanding Relative Velocity with Real-Life Examples:

  1. Car on a Highway: Imagine you’re driving a car at 60 km per hour (kmph) on a highway, and you pass another car traveling at 50 kmph in the same direction. To a passenger in your car, the relative velocity of the other car is 60 kmph – 50 kmph = 10 kmph in the same direction.
  2. Riverboat Crossing: Suppose you’re on a riverboat moving downstream at 10 kmph, and you see a swimmer in the river swimming upstream at 2 kmph. The relative velocity of the swimmer from the perspective of the riverboat is 10 kmph + 2 kmph = 12 kmph downstream.
  3. Aircraft in the Sky: In aviation, understanding relative velocity is crucial for air traffic control. An aircraft’s groundspeed is its actual speed relative to the ground, while its airspeed is its speed relative to the air. Wind can affect these speeds, causing variations in the aircraft’s motion relative to the ground.
  4. Walking on a Moving Sidewalk: When you walk on a moving sidewalk / walking escalator at an airport, you experience relative velocity. If you walk at a speed of 3 km per hour on a moving sidewalk that’s moving at 4 km per hour, from the perspective of someone standing still outside the sidewalk, you appear to be moving at 7 km per hour (3 kmph + 4 kmph).
  5. Reviewing LBW Decisions: Understanding the relative velocity of the ball concerning the batsman’s leg position can be crucial when reviewing LBW (Leg Before Wicket) decisions. It helps assess whether the ball would have hit the stumps or not.


Key Takeaways:

  1. Relative velocity depends on the observer’s point of view.
  2. When two objects move in the same direction, their relative velocity is the difference between their individual velocities.
  3. When two objects move in opposite directions, their relative velocity is the sum of their individual velocities.

Applications in the Real World:

Understanding relative velocity is crucial in various fields, including physics, engineering, and navigation. It’s used in the design of transportation systems, navigation systems, and even in everyday scenarios like overtaking another vehicle on the road.

Relative velocity has numerous practical applications in various fields. Here are some examples:


  1. Navigation and Aviation: In aviation and navigation, relative velocity is used to calculate the speed and direction of an aircraft or vessel relative to the ground. This is crucial for flight planning, route optimization, and ensuring safe travel.
  2. Traffic Engineering: Relative velocity is applied in traffic engineering to determine the speed and movement of vehicles on the road. It helps design traffic signals, analyze congestion patterns, and improve road safety.
  3. Sports: In sports like soccer, football, or rugby, understanding relative velocity helps players anticipate the movement of the ball and make accurate passes or interceptions. It’s also used in sports analytics to analyze player performance and strategies.
  4. Astronomy: Relative velocity is vital in astronomy for calculating the motion of celestial objects such as planets, stars, and galaxies. It helps astronomers understand the relative positions and velocities of celestial bodies in the universe.
  5. Rocket Science: In rocket science, relative velocity is essential for launching spacecraft, aligning orbits, and docking with other space objects like satellites or space stations. Precise calculations are required to ensure successful space missions.
  6. Physics Experiments: Scientists use relative velocity in various physics experiments to study the motion of particles, molecules, and atoms. It aids in understanding collision dynamics and particle interactions.
  7. Engineering Design: Engineers apply relative velocity when designing complex machinery and systems. For example, in the design of conveyor belts, engineers consider the relative velocities of different components to ensure smooth operation.
  8. Automotive Industry: Relative velocity is utilized in vehicle safety systems, such as collision detection and avoidance systems. These systems assess the relative velocities between a vehicle and obstacles to trigger warnings or apply brakes if necessary.
  9. Weather Forecasting: In meteorology, relative velocity helps meteorologists analyze wind patterns, track the movement of weather systems, and predict weather conditions. This information is crucial for weather forecasting and storm tracking.
  10. Marine and Oceanography: Oceanographers use relative velocity to study ocean currents, wave patterns, and the movement of marine life. It aids in understanding ocean dynamics and its impact on marine ecosystems.
  11. Military and Defense: Relative velocity is employed in military applications for targeting, missile guidance, and artillery calculations. It helps determine the relative velocity between a target and a weapon system.
  12. Robotics: In robotics, relative velocity is crucial for controlling the motion of robotic arms, drones, and autonomous vehicles. It ensures precise movement and coordination in robotics applications.


These examples demonstrate the versatility of relative velocity in various fields, where it plays a vital role in understanding, analysing, and controlling the motion of objects and systems.

Fun facts on relative velocity to make it more understandable:

  1. Racecar Drafting: In motorsports, like Formula 1 or NASCAR, drivers often “draft” behind another car to reduce air resistance. This happens because the relative velocity of the car behind is lower in the slipstream, allowing for higher speeds and exciting overtaking maneuvers.
  2. Riverboat Racing: Imagine two boats racing on a river. If they both travel at the same speed relative to the water but in opposite directions, it’s like a thrilling race, and their relative velocity is the sum of their speeds!
  3. Speed of Sound: When you’re on a fast-moving train, the relative velocity of sound changes. You can experience this when a train’s whistle sounds higher-pitched as it approaches you and lower-pitched as it moves away.
  4. Airplane Skydiving: Skydivers often jump out of airplanes flying at high speeds. During free fall, their relative velocity to the plane is initially zero, but it gradually increases as they fall faster than the plane.
  5. Rearview Mirror Illusion: In your car’s rearview mirror, the cars behind you may seem to move very slowly or standstill, especially if they are driving at nearly the same speed as you. It’s all about relative velocity!
  6. Earth’s Rotation: Even though Earth rotates at about 1670 kilometers per hour at the equator, we don’t feel it because everything on Earth’s surface, including us, shares the same velocity due to Earth’s rotation.
  7. Rocket Launch: When a rocket launches into space, it needs to reach a certain relative velocity to escape Earth’s gravitational pull. This velocity is called “escape velocity,” and it’s over 42,233 km per hour!
  8. Sports Interceptions: In sports like football or soccer, a player can intercept a pass by running to the right spot at the right time. Understanding the relative velocity of the ball and the players is key to making those exciting interceptions.
  9. Hiking Challenge: If you go hiking in the mountains and want to reach a destination, like a waterfall, the relative velocity of your hike will depend on your speed and the speed of the water flowing down the stream.
  10. Roller Coaster Thrills: On a roller coaster, you feel exhilarated because the relative velocity between you and the coaster changes rapidly as you zoom through loops, turns, and drops.


Understanding relative velocity can add a layer of excitement and wonder to everyday experiences. It’s like having a superpower that lets you see how everything around you is moving and interacting, making the world of physics come alive!


Question-answer trivia on relative velocity:


  1. What is relative velocity? Relative velocity is the velocity of an object as observed from another object’s perspective. It depends on the frame of reference of the observer.
  2. How is relative velocity calculated when two objects move in the same direction? Answer: When two objects move in the same direction, their relative velocity is the difference between their individual velocities.


  1. When two objects move in opposite directions, how is their relative velocity calculated? Answer: When two objects move in opposite directions, their relative velocity is the sum of their individual velocities.
  2. In a car race, Car A is moving at 80 km/h, and Car B is moving at 60 km/h in the same direction. What is the relative velocity of Car A concerning Car B? Answer : The relative velocity of Car A concerning Car B is 20 km/h (80 km/h – 60 km/h).
  3. Can relative velocity ever be negative? Explain. Answer: Yes, relative velocity can be negative. It occurs when two objects move in opposite directions, and the observer’s frame of reference is one of those objects. In such cases, the relative velocity is negative.
  4. In a river, Boat A is moving upstream at 5 km/h, and Boat B is moving downstream at 8 km/h. What is the relative velocity of Boat B concerning Boat A? Answer: The relative velocity of Boat B concerning Boat A is 13 km/h (5 km/h + 8 km/h).
  5. How does understanding relative velocity help in overtaking another vehicle on the road? Answer: Understanding relative velocity helps a driver calculate the speed difference needed to safely overtake another vehicle. It ensures a smooth and safe overtaking maneuver.
  6. In a relay race, Runner A runs at 10 m/s, and Runner B runs at 8 m/s in the same direction. What is the relative velocity of Runner A concerning Runner B? Answer: The relative velocity of Runner A concerning Runner B is 2 m/s (10 m/s – 8 m/s).
  7. How is relative velocity used in navigation systems like GPS? Answer: GPS navigation systems use relative velocity to calculate the speed and direction of a moving vehicle concerning a fixed point (satellites). This information helps determine the vehicle’s location and route.
  8. In the context of relative velocity, explain why it’s essential for pilots and air traffic controllers. Answer: For pilots and air traffic controllers, understanding relative velocity is crucial for safe take-offs, landings, and navigation in the airspace. It helps calculate the relative velocities of aircraft concerning each other and the ground, ensuring safe distances and flight paths.


These trivia questions can help students test their understanding of relative velocity concepts, which are relevant for JEE exam preparations in physics and engineering.