Short Answer

Relative motion is the motion of an object as observed from another moving or stationary object. It means motion is always measured with respect to a reference point or reference frame. An object may appear to be moving for one observer but may appear at rest for another.

For example, a passenger inside a moving bus may feel that another passenger is not moving, but a person standing on the road sees both passengers moving. This happens because motion depends on the observer’s position and motion, which is the basic idea of relative motion.

Detailed Explanation :

Relative Motion

Relative motion is an important concept in physics that explains how the movement of an object can look different to different observers. This concept tells us that motion is not absolute, meaning it cannot be defined without comparing it to something else. Motion must always be described with respect to a reference object or reference frame.

For example, when you sit inside a moving train, the people sitting around you appear to be at rest, but the trees outside appear to move backward. However, to a person standing outside the train, everything inside the train appears to be moving. These different observations exist because the motion is being viewed from different reference points.

Meaning of Relative Motion

Relative motion means the motion of one object with respect to another object. It focuses on comparing the movement of two things. If both objects are moving, their motion depends on their speeds, directions, and positions. Even if one object is standing still, its motion must still be measured relative to another point.

The motion observed depends on whether the observer is in a moving vehicle, standing still, or moving in the same or opposite direction as the object being observed. Therefore, relative motion helps us understand that motion is not the same for everyone.

Reference Frame in Relative Motion

A reference frame is the background or position from which an observer measures motion. It could be:

• A stationary object like a tree or a building
• A moving object like a car, train, or airplane
• The Earth itself

When an observer changes the reference frame, the observation of motion also changes.

For example:

• A person inside a train uses the train as a reference frame.
• A person standing outside uses the ground as a reference frame.

Both observers see the motion differently because their reference frames are different.

Examples to Understand Relative Motion

Relative motion is best understood through simple, everyday examples:

1. Passengers in a Train

Two passengers sitting inside a train appear to be at rest relative to each other because their distance does not change. But someone outside the train will see both passengers moving along with the train.

2. Cars Moving on a Road

If two cars move side by side at the same speed, they appear to be at rest relative to each other, even though both are moving. But a person standing on the footpath sees both cars moving quickly.

3. Walking Inside a Moving Bus

If you walk forward inside a moving bus, your motion appears different to someone inside the bus compared to someone outside.

• To the passenger inside, you move slowly.
• To the person on the road, your overall speed combines your walking speed and the bus’s speed.

4. Airplanes in the Sky

A person inside an airplane sees the seats and passengers as stationary. But someone on the ground sees the airplane moving very fast.

These examples show that motion depends on the observer’s viewpoint.

Relative Velocity

Relative motion also introduces the idea of relative velocity, which means the velocity of one object is measured relative to another. The relative velocity depends on whether objects are moving in the same direction or opposite directions.

• If two vehicles move in the same direction, their relative velocity is the difference between their speeds.
• If they move in opposite directions, their relative velocity is the sum of their speeds.

Relative velocity helps in understanding how fast one object appears to move compared to another.

Importance of Relative Motion

Relative motion is important because:

• It helps understand how motion is observed differently from different positions.
• It is used in navigation of ships and airplanes.
• It is essential in studying the motion of planets and stars.
• It explains why motion cannot be defined without a reference frame.

Scientists rely on relative motion to study the movement of bodies in physics, astronomy, and engineering.

Everyday Use of Relative Motion

Relative motion is not only a scientific idea—it is also part of our daily experiences. When sitting in a vehicle, watching moving objects, or even riding a bicycle, we are always viewing motion relative to something else. This makes our understanding of motion more practical and realistic.

Conclusion

Relative motion is the motion of one object as seen from another object. It cannot be defined without choosing a reference point or reference frame. The motion observed changes based on the observer’s position and whether the observer is moving or stationary. This concept explains why motion looks different to different people and helps us understand real situations involving movement.