Newton's First Law of Motion is also known as the law of: (a) acceleration (b) inertia (c) action and reaction

Concept understanding — Newtons First Law

Imagine you are sitting in a bus that is stopped at a traffic light. The bus lurches forward suddenly. What happens to you? You are thrown backward against your seat. Now imagine the bus is moving at a steady speed and the driver slams the brakes. You lurch forward, toward the front of the bus. You have felt Newton's First Law without knowing its name.

The core idea is simple: things like to keep doing what they are already doing. If an object is sitting still, it wants to stay still. If it is moving in a straight line at a steady speed, it wants to keep moving exactly like that. Nothing changes unless something else forces it to change.

This is not a guess. It is a fundamental observation about how the world works. Before Newton, people thought a moving object needed a constant push to keep moving — that rest was the "natural" state. Newton saw the opposite: both rest and steady straight-line motion are equally natural. A ball rolling across a rough floor slows down because the floor pushes against it (friction), not because motion itself is unnatural. If you could remove all friction and air resistance, that ball would roll forever.

Note

The formal name for this "keep doing what you are doing" property is inertia. Newton's First Law is often called the Law of Inertia. Inertia is not a force — it is a resistance to change. A heavy suitcase has more inertia than a feather; it is harder to start moving and harder to stop once moving.

Why does this matter for someone who will never calculate a force? Because it changes how you think about cause and effect. Every time you see something speed up, slow down, or turn, you know a cause — a push or a pull — must be present. When a car turns a corner and you slide to the outside of the seat, it is not a mysterious "centrifugal force" throwing you. Your body is simply obeying the First Law: it wants to keep going straight. The car door pushes you inward, forcing you to turn. You feel that push.

The law also explains why seatbelts exist. When a car crashes and stops abruptly, your body keeps moving forward at the original speed. The seatbelt provides the force that stops you from continuing through the windshield. Without it, nothing would stop you until you hit something else.

Important

Newton's First Law is not about what happens when nothing acts on an object — that almost never happens on Earth. It is about identifying when a change is happening and knowing that a force must be the reason. If you see a change in motion, look for the force. If you see no change in motion, the forces are balanced — they cancel each other out. This is the foundation for understanding everything from why a book stays on a table to why planets orbit the Sun.

In short: objects are lazy about changing their motion. They need a reason to change. That reason is always a force. Once you see the world this way, you start noticing forces everywhere — the push of the ground on your feet as you walk, the drag of air on a moving car, the pull of gravity on a falling leaf. The First Law gives you a lens to see the invisible pushes and pulls that shape every moment of your day.

Newton's First Law is known as the law of inertia because it describes an object's resistance to changes in its state of motion.

Understanding Newton's First Law

Newton's First Law states that an object at rest stays at rest, and an object in motion continues in motion with the same speed and in the same direction, unless acted upon by an unbalanced external force. This fundamental principle reveals a property inherent to all matter: inertia.

Inertia is the tendency of an object to resist any change in its state of motion. A heavier object has more inertia than a lighter one, which is why it's harder to start moving a loaded cart than an empty one, and equally harder to stop it once it's rolling. The law doesn't describe how motion changes (that's the Second Law) or the mutual nature of forces (that's the Third Law) — it simply establishes that objects "want" to maintain their current state unless compelled to change.

In sports and physical activity, you experience this constantly. A sprinter must overcome her body's inertia to accelerate from the blocks. A football in flight continues its path until air resistance, gravity, or a player's foot changes its motion. A gymnast rotating in the air will keep rotating at the same rate unless she tucks or extends her limbs to redistribute her mass.

Evaluating the Options

(a) Acceleration — Newton's Second Law (F = ma) governs acceleration, relating the net force on an object to the acceleration it produces. The First Law doesn't quantify acceleration; it describes the condition when acceleration is zero.

(c) Action and reaction — Newton's Third Law states that for every action there is an equal and opposite reaction. This describes force pairs between interacting objects, not the resistance to motion change.

(d) Gravitation — Newton's Law of Universal Gravitation describes the attractive force between masses. It's a separate principle entirely, unrelated to inertia or the First Law.

✓Final answer

The correct option is (b) — inertia . Newton's First Law is universally known as the law of inertia because it defines inertia as the property by which objects resist changes to their motion.

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Q.Newton's First Law of Motion is also known as the law of:

Understanding Newton's First Law

Evaluating the Options

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