Inertia is a property of objects that resist any change in their state of motion - at rest or in uniform motion. An object with greater inertia will be harder to accelerate or decelerate. If the Earth were to have inertia, it would be more difficult for the planet to rotate on its axis and orbit around the Sun. The days and nights would become longer, and the Earth's seasons would change more drastically. Additionally, any changes in the Earth's orbit or rotation would be much more gradual and difficult to observe.