Orbital Sandbox
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flagWhat you'll discover
- arrow_forwardLaunch a body into a stable orbit by hand
- arrow_forwardExplain an orbit as "falling sideways forever"
- arrow_forwardPredict what happens when speed is too low or too high
- arrow_forwardObserve how star mass changes the needed orbital speed
Gravity never switches off
Every object with mass pulls on every other object. The pull grows with mass and weakens with distance — double the distance and the force drops to a quarter. This is Newton’s law of universal gravitation, and it rules everything in this sandbox.
The star in the centre pulls on each planet you launch, every single frame, always pointing toward the star. The planet’s path is just the running total of "keep moving" plus "keep falling".
An orbit is falling sideways
Here is the secret of every satellite and planet: it is falling the whole time — it just moves sideways fast enough to keep missing the thing it is falling toward.
Throw a ball: it curves down and hits the ground. Throw it impossibly fast — about 7.8 km/s near Earth — and the ground curves away beneath it exactly as fast as it falls. It falls forever in a circle. That is what astronauts on the ISS are doing: not floating away from gravity, but falling around the Earth.
Too slow, too fast, just right
In the sandbox, a short drag gives a slow launch: gravity wins, the path bends sharply and the body spirals into the star. A huge drag gives a fast launch: gravity can’t bend the path enough and the body escapes into space.
Between those is the sweet spot — an ellipse or circle that repeats forever. Try launching at a right angle to the line toward the star. Then crank up the star’s mass and notice that the same throw now crashes: stronger gravity demands more sideways speed.
Comets: stretched orbits
Press "Add comet" and watch its motion. A comet on a long, stretched ellipse races fastest when it whips around the star and crawls when far away. Nothing pushes or brakes it — gravity simply steals speed on the way out and pays it back on the way in. Energy is conserved.
Real comets do exactly this: Halley’s comet sprints past the Sun, then drifts out beyond Neptune for decades before falling back. You will meet this speed-up/slow-down pattern again in the Kepler lesson.