Inertia in science is the natural tendency of objects to resist changes in their state of motion. This means that an object at rest tends to stay at rest, and an object in motion tends to continue moving at a constant velocity in a straight line unless acted upon by an external force. This principle is encapsulated in Isaac Newton's first law of motion, also known as the law of inertia
. Inertia is not a force itself but a property of matter that reflects how much an object resists changes in its motion. The amount of inertia an object has depends solely on its mass-the greater the mass, the greater the inertia. For example, a heavy object like a train has much more inertia than a light object like a bicycle, making it harder to start or stop the train's motion
. Historically, the concept was first formulated by Galileo and later refined by Newton, who described inertia as an innate force of matter resisting changes in motion. Today, inertia is understood simply as the phenomenon of resistance to changes in motion, without attributing it to any specific internal force
. In everyday life, inertia explains why passengers lurch forward in a car when it suddenly stops or why a coin stays in place when a card underneath it is quickly pulled away-the coin resists changes to its state of rest due to inertia
. In summary, inertia is the property of matter that causes it to maintain its current state of motion or rest unless influenced by an external force, and it is fundamentally linked to the mass of the object
