Universal Gravitation in Physics

The same pull that drops an apple holds the Moon in its path, and writing that down as one equation was the first time physics explained the sky and the ground together. The force is proportional to both masses and falls away with the square of the distance, which is why a satellite a few hundred kilometres up still feels almost the full pull of gravity and only seems weightless because it keeps falling sideways. Field strength is that force per unit mass, and it is the concept that lets the same rules apply far from any planet. The blocks give the force, the field it produces inside and outside a body, the potential energy that comes with it, and the two speeds that govern orbits.