The essential principles of gravity depend on several critical variables. These are the objects’ mass – the larger the mass, the stronger the pull – and the distance between objects, which, with the increase, weakens the force with which these objects are pulled toward each other (Heppler, 2018). The mass of the Earth is sufficient to exert a strong gravitational pull on the surrounding objects and thus prevent them from ‘floating’ away from its surface. However, the objects farther away, like the International Space Station (ISS), experience a lesser gravitational pull than those located directly on the surface.
Nonetheless, if the ISS were launched at a low speed, it would get pulled back or, effectively, fall. It does not happen because of the sufficient speed of sending a projectile outward: when a projectile is ejected, it then starts falling back due to the gravitational pull, forming a curve (Basics of space flight – Solar system exploration, n.d.). The larger the velocity with which it is ejected, the wider the curve, ensuring a longer travel time for the launched object (Basics of space flight – Solar system exploration, n.d.). Therefore, a high enough speed may create a wide enough curve for the accelerated object to fit Earth’s curvature, enabling it to orbit around it due to a centripetal force (Heppler, 2018). In the situation where the gravitational and centripetal forces that the orbiting ISS experiences are equal, it may continue circling, ‘missing’ the Earth each time (Heppler, 2018). The ISS travels at about 17,150 miles an hour, which is enough to keep it in balance (Heppler, 2018). The exact balance of centripetal force and the gravitational force causes the Moon to orbit the Earth and the Earth to orbit the Sun (Basics of space flight: Solar system exploration, n.d.). Overall, the physics of orbiting underlying objects’ movement in space depends on the balance of the opposing forces and specific speeds.
References
Basics of Space Flight – Solar System Exploration: NASA Science. (n.d.). NASA Solar System Exploration.
Heppler, L. (2018). Free falling: The science of weightlessness. Science in the News.