>Gravity isnt a real force. It is and you can measure it. >How is the admittedly weakest force supposed to hold on to lonely particles on the edge of a vacuum, all while the earth is (allegedly) spinning and hurling through three dimensions? There isn't a hard "edge" to the atmosphere. Earth's gravity is strong enough to hold you down, and gases like nitrogen and oxygen (at the Earth's temperature). But it's not strong enough to hold on to the lightest gases - hydrogen and helium. The molecules in a gas have their velocities distributed as in the below diagram: https://cpb-ca-c1.wpmucdn.com/blog44.ca/dist/a/4/files/2012/09/Boltzmann-distribution-KE-copy-2bm614m.jpg Ceteris paribus, the molecules in a hotter gas will have higher gas will move faster. Also, lighter molecules move faster. Some fraction of the molecules in the right tail of the distribution will have a velocity higher than the escape velocity of the planet; those molecules will be lost to outer space. A planet the size of Earth could only retain hydrogen and helium if it were further from the Sun and hence colder. Earth's rotation gives rise to a small centrifugal force. You weigh less at the equator than at the poles for this reason. But not a lot less. The speed of Earth's orbital motion makes no difference. It's acceleration that counts - but the atmosphere is accelerated by the Sun's gravity just like the rest of the planet, so there's no tendency for it to pull away from the surface (more or less - the atmosphere actually is affected by tidal forces just like the oceans.)