The Falling Loop: Why Satellites Stay in Orbit

If gravity pulls a satellite toward the Earth and inertia wants it to travel in a straight line, then the balance between these two prevents the satellite from either falling to the ground or flying away into deep space.

If gravity were zero, then a satellite would travel in a straight line away from Earth due to inertia; because satellites move in a curved path, we know an inward force like gravity is still pulling on them.

If you fire a cannonball fast enough that the curve of its fall matches the curvature of the Earth, then the ball will never hit the ground. Newton used this logic to show how gravity and speed create an orbit.

If an object resists changes to its state of motion, and if this resistance is a fundamental property of mass, then the scientific term for this behavior is inertia.

If the law of universal gravitation states that force equals G * (m1 * m2) / r^2, then the masses of both objects and the distance between their centers are the only physical factors that matter.

If the forward motion (inertia) is not fast enough to overcome the inward pull of gravity, then the satellite's path will curve too sharply toward the center, causing it to fall.

If gravity is stronger closer to a planet's mass, then a satellite needs more forward velocity to "miss" the Earth; therefore, lower-altitude satellites must move much faster to maintain a stable orbit.

If an object is captured by gravity and moves in a repeating loop around a larger body, then that specific trajectory is defined as an orbit.

If no force were acting on the satellite, Newton's First Law states it would move in a straight line forever; in a circle, this straight-line path is always perpendicular (tangent) to the pull of gravity.

If a satellite is "falling" around the Earth and you are inside it falling at the same speed, then you do not feel any support force; this creates the sensation of weightlessness even though gravity is present.

If air molecules hit a satellite, they create friction that slows the satellite down; if the satellite slows down, it loses the inertia needed to stay in space and will eventually crash.

If a satellite orbits at a specific altitude where its period matches the Earth's 24-hour rotation, then it will appear to hover over one fixed location on the surface.

If an object is moving in a circle, it must have a center-seeking force pulling it away from its straight-line path; in space, gravity acts as this centripetal force.

If the International Space Station is to maintain its height against Earth's strong gravity, then it must travel at approximately 17,500 mph (7.6 km/s) to ensure its curve of falling matches the Earth's curve.

If we can place sensors in a stable position above Earth, then we can use them to send signals, take pictures of clouds, or track locations; however, satellites cannot physically mine the bottom of the ocean.

If there is no air in the vacuum of space to cause friction, then according to the law of inertia, an object in motion will stay in motion at the same speed without needing any extra push from an engine.

If the satellite moves faster, its "outward" inertial tendency increases; if inertia becomes stronger than the current gravitational pull, the satellite will push into a larger, more distant path.

If the path of the satellite takes it over the Earth's rotational axes (the poles) while the Earth spins beneath it, then the orbit is classified as a polar orbit.

If the Earth is already spinning at about 1,000 mph at the equator, then launching in the same direction adds that existing speed to the rocket, which saves fuel and makes reaching orbital velocity easier.

If an orbit is a balance of forces, then speed and distance are the primary variables; if air resistance were present, it would ruin the balance by slowing the object down.