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How does inertia affect an object at rest or in motion?

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principles of physical science Figure 1: Data in the table of the Galileo experiment. The tangent to the curve is drawn at t = 0.6.

In the principles of physical science, inertia is the inherent property of a body that causes it to oppose any agency attempting to change its state of motion.12

According to the law of inertia, which serves as the foundation of classical mechanics, an object will remain at rest or continue moving at a constant speed in a straight line unless acted upon by an external force.34

It is a common misconception that objects naturally come to rest; in reality, observations of objects slowing down are due to unbalanced forces such as friction or air resistance. Inertia is a passive property, meaning a body does not actively maintain its motion; rather, it simply resists changes to its velocity or state of rest. This resistance is numerically measured by an object's mass (for linear motion) or its moment of inertia (for rotational motion).3421