A long jumper runs before jumping because he

1. Newton’s First Law and the Concept of Inertia (basic)

Imagine a book lying on a study table. It will remain exactly there for days, years, or even centuries unless someone picks it up or a strong wind moves it. Conversely, if you slide a puck on a perfectly smooth, frictionless sheet of ice, it would theoretically glide forever in a straight line. This fundamental property of nature is Newton’s First Law of Motion, often called the Law of Inertia. It states that every object will continue in its state of rest or uniform motion in a straight line unless it is compelled to change that state by an external force. In essence, matter is "lazy"—it resists any change to its current state of motion. This resistance is what we call Inertia. It is not a force, but a property of mass. To change an object's speed or direction, an external force must be applied, as explored in Science Class VIII NCERT (Revised ed 2025), Exploring Forces, p.64. Without such a force, an object follows linear motion—moving along a straight path at a constant speed Science Class VII NCERT (Revised ed 2025), Measurement of Time and Motion, p.116. For example, if a car travels at different speeds over different hours, we know its motion is non-uniform because external forces (like the engine or brakes) are constantly overcoming its inertia to change its velocity. In practical terms, we experience inertia every day. When a bus suddenly starts moving, your body jerks backward because your lower body moves with the bus while your upper body tries to remain at rest (inertia of rest). Conversely, when a long jumper runs before taking a leap, they are building up inertia of motion. Once they leave the ground, their body naturally "wants" to continue moving forward at that high velocity, allowing them to cover a much greater horizontal distance than if they had jumped from a standing position. Even on a planetary scale, the Rotation of the Earth is a form of persistent motion that continues due to the immense inertia of our planet Physical Geography by PMF IAS, The Motions of The Earth and Their Effects, p.267.

Sources: Science Class VIII NCERT (Revised ed 2025), Exploring Forces, p.64; Science Class VII NCERT (Revised ed 2025), Measurement of Time and Motion, p.116; Physical Geography by PMF IAS, The Motions of The Earth and Their Effects, p.267

2. Linear Momentum: The Quantity of Motion (basic)

When we observe objects in motion, we instinctively feel that some are harder to stop than others. Imagine a massive truck and a light bicycle both moving toward you at the same speed. You would naturally find the truck far more intimidating. This "quantity of motion" an object possesses is what physicists call Linear Momentum. It is a fundamental property of any object moving along a straight path, also known as linear motion Science-Class VII, Measurement of Time and Motion, p.116.

Momentum is not just about how fast you are going; it is the combined effect of an object's mass (how much matter it has) and its velocity (its speed in a specific direction). Mathematically, it is expressed as the product of these two factors: p = mv. Because velocity has a direction, momentum is also a vector quantity, meaning it points in the same direction as the object's movement. For example, if a proton moves freely in a magnetic field, its momentum can change even if its mass remains constant, simply by changing its velocity Science, class X, Magnetic Effects of Electric Current, p.203.

To understand why momentum matters, consider how forces interact with it. A force is required to change the speed or direction of a moving object Science-Class VIII, Exploring Forces, p.64. This change in motion is essentially a change in the object's momentum. An object with high momentum (like a fast-moving train or a heavy boulder) requires a significantly larger force, or a force applied over a longer time, to come to a complete stop compared to an object with low momentum.

Scenario	Mass	Velocity	Resulting Momentum
Heavy truck (slow)	High	Low	High
Bullet (fast)	Low	Very High	High
Bicycle (slow)	Low	Low	Low

Sources: Science-Class VII . NCERT(Revised ed 2025), Measurement of Time and Motion, p.116; Science-Class VIII . NCERT(Revised ed 2025), Exploring Forces, p.64; Science , class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.203

3. Newton’s Second Law: Force and Change in Momentum (intermediate)

To understand how motion changes, we must first look at a concept called Momentum (denoted by 'p'). Think of momentum as the 'quantity of motion' an object possesses. It is the product of an object's mass (m) and its velocity (v), expressed as p = mv. As noted in Science, Class X, Magnetic Effects of Electric Current, p.203, momentum is a critical property of a moving particle that changes whenever its velocity changes. Newton’s Second Law of Motion takes this further by explaining how force interacts with momentum. It states that the rate of change of momentum of an object is directly proportional to the applied unbalanced force in the direction of the force. In simpler terms, if you want to change how fast or in what direction something is moving, you must apply a force. The formula looks like this: F ∝ Δp / t (where Δp is the change in momentum and t is the time taken). From this, we derive the famous F = ma (Force = mass × acceleration), because acceleration is simply the rate of change of velocity. A crucial nuance of this law is the role of time. Since Force is equal to the change in momentum divided by time, increasing the time taken to stop or start an object reduces the force experienced. This is why a long jumper lands in a sandpit; the sand increases the time it takes for their momentum to drop to zero, thereby reducing the impact force on their legs. Conversely, in a run-up, the athlete spends time applying force against the ground to steadily build up a high velocity, maximizing their momentum before takeoff.

Scenario	Momentum Change (Δp)	Time (t)	Resulting Force (F)
Catching a ball by pulling hands back	Constant	High (Increases)	Low (Soft impact)
Stopping a car by hitting a wall	Constant	Low (Instant)	Very High (Dangerous impact)

Sources: Science, Class X (NCERT 2025), Magnetic Effects of Electric Current, p.203; Science, Class VIII (NCERT 2025), Exploring Forces, p.77

4. Connected Concept: Conservation of Momentum (intermediate)

In our journey through mechanics, we now reach a fundamental pillar: Momentum. At its simplest, momentum is the "quantity of motion" an object possesses. It is calculated as the product of an object's mass (m) and its velocity (v). Mathematically, we express this as p = mv. Because velocity has a direction, momentum is a vector quantity, meaning the direction in which an object moves is just as important as how fast it is going.

The Law of Conservation of Momentum is a universal principle stating that if no external force acts on a system, the total momentum of that system remains constant over time. This means that in a closed environment—like two billiard balls colliding or a rocket launching—the momentum lost by one object is exactly gained by another. Even if the objects change their individual speeds or directions, the "mathematical sum" of their motion stays the same.

To see this in action, consider a long jumper. Why do they sprint before the jump? They are intentionally building up horizontal momentum. By increasing their velocity during the run-up, they maximize their p (momentum). At the point of takeoff, this accumulated momentum provides the inertia of motion necessary to carry their body forward through the air. While they must convert some of this into vertical lift to stay airborne, it is the preserved horizontal momentum that ultimately determines how far they land from the board. This illustrates how momentum acts as a "buffer" of motion that keeps us moving even after we stop pushing off the ground.

Much like how a magnetic field can cause a displacement of a rod by applying a force, as discussed in Science, Class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.204, physical motion is always governed by the interaction of forces and the resulting changes in momentum. Understanding that momentum is conserved helps engineers design everything from car safety airbags to interplanetary probes.

Sources: Science, Class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.204

5. Connected Concept: Kinetic Energy and Work (intermediate)

To understand mechanics, we must look at Kinetic Energy (KE) as the energy of motion. In the physical world, this energy is everywhere: from the thermal energy we feel as sensible heat—which is actually the vibrational kinetic energy of dense atmospheric molecules Environment and Ecology, Majid Hussain, BASIC CONCEPTS OF ENVIRONMENT AND ECOLOGY, p.8—to the primordial heat of the Earth, which originated from the kinetic energy of meteorite impacts during our planet's formation Physical Geography by PMF IAS, Manjunath Thamminidi, Earths Interior, p.59. In basic mechanics, KE is defined by the formula KE = ½mv², meaning it depends on an object's mass (m) and the square of its velocity (v).

The bridge between a stationary state and motion is Work. According to the Work-Energy Theorem, the work done by a force on an object is equal to the change in its kinetic energy. When a force is applied to change an object's speed or direction Science, Class VIII, NCERT, Exploring Forces, p.64, energy is being transferred. A classic example is a long jumper. The athlete performs an intense 'approach run' to do work on their own body. This work increases their horizontal velocity, thereby maximizing both their kinetic energy and their momentum (p = mv) at the moment of takeoff.

Why is this sprint so vital? Because in the air, the athlete relies on the inertia of motion to continue moving forward. The higher the velocity achieved during the run-up, the more momentum they carry into the jump. While the jumper must convert some of this horizontal drive into vertical lift, the distance they cover is ultimately a product of how much speed they successfully generated and maintained during their approach Science-Class VII, NCERT, Measurement of Time and Motion, p.119.

Concept	Mathematical Relation	Role in Long Jump
Kinetic Energy	Proportional to Velocity squared (v²)	The energy 'stored' in the athlete's speed.
Momentum	Product of Mass and Velocity (mv)	The 'quantity of motion' that carries the jumper forward.
Work	Force × Displacement	The effort during the run-up to gain speed.

Sources: Environment and Ecology, Majid Hussain, BASIC CONCEPTS OF ENVIRONMENT AND ECOLOGY, p.8; Physical Geography by PMF IAS, Manjunath Thamminidi, Earths Interior, p.59; Science, Class VIII, NCERT, Exploring Forces, p.64; Science-Class VII, NCERT, Measurement of Time and Motion, p.119

6. Inertia of Motion in Athletics and Daily Life (exam-level)

In physics, Inertia is the inherent tendency of an object to resist any change in its state of rest or motion. When we focus on Inertia of Motion, we are looking at the property that keeps an object moving in the same direction and at the same speed unless an external force intervenes. In our daily experience, we often see this when a car suddenly brakes and our bodies lunge forward; our lower body stops with the car, but our upper body "wants" to continue moving at the previous speed.

In athletics, specifically the long jump, this principle is utilized to maximize performance. An athlete does not simply stand at the edge and jump; they perform a rapid approach run. As noted in Science-Class VII . NCERT(Revised ed 2025), Measurement of Time and Motion, p.113, a faster runner covers more distance in the same amount of time, possessing a higher speed. By sprinting, the athlete builds up momentum — which is the product of their mass and their velocity. This accumulated momentum acts as a reservoir of motion that the athlete carries into the air.

The magic happens at the point of takeoff. Once the athlete's feet leave the ground, the force of their muscles is no longer pushing them forward. However, because of Inertia of Motion, their body resists stopping. The high horizontal velocity gained during the run-up ensures that they continue to travel forward through the air at a high speed. While gravity eventually pulls them down, the inertia allows them to cover the maximum possible horizontal distance before landing. This transition from a fast, often non-uniform run to a flight phase is a perfect example of how linear motion principles are applied in sports Science-Class VII . NCERT(Revised ed 2025), Measurement of Time and Motion, p.116.

Sources: Science-Class VII . NCERT(Revised ed 2025), Measurement of Time and Motion, p.113; Science-Class VII . NCERT(Revised ed 2025), Measurement of Time and Motion, p.116

7. Solving the Original PYQ (exam-level)

Now that you have mastered the fundamental principles of Newtonian Mechanics, you can see how the building blocks of Mass, Velocity, and Inertia translate directly from the textbook to the athletic field. The act of running before a jump is a practical application of Linear Momentum (p = mv). By sprinting during the approach, the athlete maximizes their horizontal velocity. As a coach, I want you to visualize this as the athlete "storing" motion; this accumulated momentum provides the necessary Inertia of Motion, which ensures that once their feet leave the ground, their body resists a change in its state of motion and continues to drive forward through the air.

To arrive at the correct answer, (D) gains momentum, you must distinguish between the physical mechanism and the objective. A common UPSC trap is to offer the desired result as an option, such as (A) covering a greater distance; however, distance is the outcome of the jump, whereas the question asks for the physical reason why the run-up is performed. Similarly, while the athlete does increase their kinetic energy, momentum is the more precise concept here because it accounts for the directional drive required to maintain horizontal speed against the vertical transition of the jump. You should also dismiss (B) momentum conservation, as that principle typically applies to closed systems or collisions, not an individual accelerating through muscular effort as noted in Research Online LJMU.