A heavier object possesses greater inertia than a lighter object.
Explanation
Inertia is the inherent property of a body by virtue of which it resists any change in its state of rest or of uniform motion in a straight line. According to Newton's First Law of Motion, the inertia of an object is measured solely by its mass. It is independent of the object's velocity, shape, or volume.
Analysis of Options:
- A fast-moving light object has more inertia than a slow-moving heavy object. is incorrect: Inertia depends exclusively on mass, not on speed or velocity. A fast-moving light object has less inertia than a slow-moving heavy object because its mass is lower. While the fast-moving object may have high momentum, its inertia (resistance to change in motion) remains low.
- Two objects of the same size always possess equal inertia. is incorrect: Size (volume) does not determine inertia; mass does. Two objects of the same size can have different masses if their densities differ (e.g., a plastic ball vs. an iron ball of the same radius). Consequently, they will have unequal inertia.
- An object in free fall possesses zero inertia. is incorrect: An object in free fall is under the influence of gravity, but its mass remains unchanged. Since mass is the measure of inertia, the object retains its inertia even during free fall.
- A heavier object possesses greater inertia than a lighter object. is correct: Since mass is the quantitative measure of inertia, a heavier object (one with greater mass) inherently possesses greater inertia than a lighter object. It requires a greater force to change its state of motion.
Key Takeaway:
Inertia is directly proportional to mass ($I \propto m$). It is an intrinsic property of matter and does not depend on velocity, volume, or the external forces acting on the body.