Engadgits laws of movement can be applied to objects, like the wheels of a car, or a ball of yarn, but not to the ground.
This means that a ball that moves from one place to another can be moved by the force of gravity, and a ball from one person to another, but cannot be moved because it doesn’t have mass.
This makes it a very useful tool for tracking things in motion.
For instance, a person walking on a moving bicycle can be tracked by measuring the speed of the bicycle as it goes from one spot to another.
This is useful if the person is doing a dangerous manoeuvre on the bicycle that causes them to lose control.