Physics · Laws Of Motion · NEET
No. Inertia is not a force. It is a property of matter that describes how strongly a body resists a change in its motion. A force is a push or pull that acts on a body, but inertia is just the body's own tendency to keep doing what it is already doing. Because inertia is not a force, it has no direction and no unit like the newton. This is the single most common mistake NEET students make.
Both. Inertia means resistance to any change in state. A body at rest resists being made to move (inertia of rest), and a moving body resists being stopped or having its speed or direction changed (inertia of motion). A cricket ball moving fast has a lot of inertia of motion, which is why it hurts to stop it with a bare hand.
They are closely linked but not identical. Mass is the numerical measure of inertia. A body with more mass has more inertia, so it is harder to start moving or to stop. But inertia is the concept (the tendency to resist change) while mass is the quantity (measured in kilograms). In simple words: mass tells you how much inertia a body has.
Because of the law of inertia. Once a body is moving, its own inertia keeps it moving at the same speed in a straight line. On Earth a moving ball slows down only because friction and air resistance push against it. Remove those opposing forces (like in deep space) and the body would move forever with no engine and no force. Aristotle wrongly thought motion needs a constant force; Galileo corrected this.
More mass means more inertia. A loaded truck is much harder to push and much harder to stop than an empty cycle, because the truck has far more mass and therefore far more inertia. NEET options often try to trap you by reversing this, so always link 'more mass' to 'more inertia' to 'harder to change motion'.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Inertia is the tendency of a body to keep doing what it is already doing. If it is at rest it stays at rest, and if it is moving it keeps moving in a straight line at the same speed, until an external force changes that.
Galileo Galilei arrived at the law of inertia from his experiments on inclined planes. Isaac Newton later restated it as his first law of motion, so it is also called Newton's first law.
Mass is the measure of inertia. The greater the mass of a body, the greater its inertia, and the harder it is to change its state of rest or motion.
Every body continues in its state of rest or of uniform motion in a straight line unless it is acted upon by a net external force. This is the law of inertia, also known as Newton's first law of motion.
Inertia is the base concept for Newton's first law, momentum and all of the Laws of Motion chapter. NEET regularly asks conceptual questions that test whether you know inertia is a property (mass), not a force, so getting it clear here saves marks later.
