In classical mechanics: The inherent property of a body that resists any change in its state of rest or uniform straight-line motion is called ________.

Introduction / Context:
One of the most fundamental ideas in Newtonian mechanics is the tendency of bodies to maintain their current state of motion unless acted upon by an external unbalanced force. This resistance to change is a hallmark of inertial behavior and connects directly to Newton’s First Law and the concept of inertial reference frames.

Given Data / Assumptions:

• No external unbalanced forces act on the body (idealized case).
• Motion is measured in an inertial frame (non-accelerating frame).
• Uniform motion means constant velocity (constant speed in a straight line).

Concept / Approach:
Inertia is the property of matter that resists changes in velocity (both speed and direction).Mass quantifies inertia numerically; greater mass means greater resistance to acceleration under the same applied force.Momentum (p = m * v) describes the quantity of motion but is not itself the “reluctance” property.Weight (W = m * g) is a gravitational force, not a property of resistance to kinematic change.

Step-by-Step Solution:

Verification / Alternative check:
From Newton’s Second Law: a = F / m. For a given force F, a larger mass m yields smaller acceleration, confirming mass as the measure of inertia and “inertia” as the property being tested.

Why Other Options Are Wrong:

• Momentum: Depends on velocity; it is not the “reluctance to change.”
• Mass: Numerical measure of inertia, not the name of the property asked.
• Weight: Force due to gravity; changes with location (g).
• Impetus: Historical term, not standard in modern mechanics.

Common Pitfalls:
Confusing the property (inertia) with its measure (mass) or with gravitational force (weight).

Final Answer:
Inertia