This would be Newton’s second law of motion. It is the amount of force applied to an object to make its mass accelerate. It basically means that something at rest will stay at rest unless it is acted upon. This is why people find it easy to stay up until 6 AM, but find waking up at the same time to be incredibly difficult. Or why a car needs to be given some gas to go, and as soon as the gas is let up, the car starts to slow down. It needs an outside force to make it go.
The equation associated with this law of motion is F=MA, as the answer before me stated underneath the answer they picked.