Physics · Laws Of Motion · NEET
No. This is the most common mistake. Inertia is a property of a body, not a force. It is only the tendency of a body to resist change in its state of rest or motion. It has no direction and is not measured in newtons. The measure of inertia is mass: more mass means more inertia. When you feel a 'push' backward as a bus starts, that is not a force of inertia - it is simply your body staying at rest while the bus moves forward under you.
Inertia of rest. Your body is at rest and wants to stay at rest. When the bus suddenly moves forward, the lower part of your body moves with the bus (it is in contact with the floor and gets pulled by friction), but the upper part stays behind for an instant due to inertia of rest. That is why you fall backward. Remember: bus STARTS = you fall BACKWARD = inertia of REST.
Inertia of rest is a body's tendency to stay at rest (example: dust flies off a carpet when beaten - the carpet moves but the dust stays behind). Inertia of motion is a moving body's tendency to keep moving (example: a passenger falls forward when a moving bus brakes suddenly - the body wants to keep moving forward). Rest = stays still; Motion = keeps moving.
Yes. Mass is the direct measure of inertia. A heavier body is harder to start moving, harder to stop, and harder to turn. That is why it is easier to push an empty cart than a loaded one, and why a loaded truck needs a longer distance to stop than a bike. Inertia depends only on mass, not on speed, shape or surface.
Inertia of direction is a body's tendency to keep moving in a straight line and resist a change in direction. Example: when a car turns sharply to the left, the passengers are pushed to the right (outward), because their bodies want to keep moving in the original straight-line direction. Another example: mud flying off tangentially from the tyre of a moving cycle, or water drops thrown off a spinning umbrella.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Inertia of rest, inertia of motion, and inertia of direction. Rest = a body at rest stays at rest. Motion = a moving body keeps moving. Direction = a body resists change in its direction of motion.
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.
Inertia of motion. The moving passenger tends to keep moving forward even when the bus stops, so the body falls forward.
They are closely linked. Newton's first law is also called the law of inertia because it states that a body keeps its state of rest or uniform motion unless an external force acts. Inertia is the property behind this law.
No. Inertia depends only on the mass of the body, not on its speed, velocity or direction of motion.
