Moment of inertia

Moment of inertia is like a spinning wheel. A spinning wheel has a lot of mass at the outside, so it takes more effort to accelerate or decelerate it. The moment of inertia of a wheel is a measure of how much effort it takes to spin it - it increases as the wheel gets bigger and has more mass, and decreases when it gets smaller and has less mass. Imagine pushing a wheel with a heavy, solid block of metal attached to the center. It's going to take a lot more effort to start spinning it and make it go faster! That's because the wheel has a larger moment of inertia.