Which of the following statements best describes inertia?
A Inertia depends on the size of an object.
B Inertia is proportional to speed.
C Inertia is a vector quantity.
D Inertia is a resistance to change in motion.
The correct answer and explanation is :
The correct answer is D: Inertia is a resistance to change in motion.
Explanation:
Inertia is a fundamental property of matter described in Newton’s First Law of Motion, often referred to as the Law of Inertia. This law states that an object will remain at rest, or continue moving in a straight line at a constant speed, unless acted upon by an external force. Inertia is the resistance an object has to changes in its state of motion—whether that involves speeding up, slowing down, or changing direction.
In simpler terms, inertia refers to the tendency of objects to “keep doing what they are doing.” If an object is stationary, it resists being set into motion. If it is already moving, it resists being stopped or having its velocity changed. The greater the inertia, the more difficult it is to change the object’s motion. This resistance to motion changes depends directly on the mass of the object—more massive objects have more inertia and are harder to accelerate or decelerate.
Why the other options are incorrect:
- A: Inertia depends on the size of an object.
While inertia is often related to the mass of an object, it is not directly about its size. The amount of inertia is more accurately described by mass rather than the physical size or dimensions of an object. - B: Inertia is proportional to speed.
Inertia is not related to an object’s speed. It is instead related to the object’s mass. Speed is a measure of how fast an object is moving, but inertia concerns how much resistance an object has to changes in that motion. - C: Inertia is a vector quantity.
Inertia is not a vector quantity. A vector quantity has both magnitude and direction, but inertia only describes the amount of resistance to a change in motion (a scalar quantity). It’s a measure of “how much” resistance, not the direction of it.
Image:
Here is an illustration that visually represents the concept of inertia. The large object with more mass has more inertia, resisting changes to its motion compared to the smaller object.