Flybys to boost speed take a tiny tiny tiny part of a planet’s orbital kinetic energy and exchange it with a spacecraft. The silliest way to describe it is kin

Flybys to boost speed take a tiny tiny tiny part of a planet’s orbital kinetic energy and exchange it with a spacecraft. The silliest way to describe it is kind of like stepping in front of a bus, but instead of actually getting hit you just get close enough for gravity to pull you along with the planet. Orbital mechanics is really just not intuitive so you can’t get an easy explanation as one doesn’t exist, your life experience with momentum and gravity is just too different for it to make sense easily.