# Inertia – definition in physics

Inertia: From Newton’s first law of motion we get the definition of inertia. As per this law, an object can’t change its state of motion by itself. If the object is static (i.e. the object is in the state of rest) it will continue to be in the state of rest unless an external force is applied on it. Similarly, If the object is in state of motion (object is moving in some direction) it will continue to move with the same speed without changing its direction unless an external force is applied on it.

Here we get the definition of inertia. Inertia is the inherent property of an object by virtue of which it tends to retain its state of rest or motion.

Mass is the measure of the inertia of an object. An object with more mass will have more inertia than that of an object of lower mass. In other words, a 10 kg object will have more tendencies to retain its state of motion or rest than an object of 5 kg mass.
That is why we need to apply more force to move or stop an object with more mass.

Example: We need larger force to set a loaded trolley in motion than an unloaded trolley. Similarly we need more force to stop a loaded trolley than the unloaded one, if both have equal initial velocity.

Inertia – definition in physics
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