Orbital motion
How does an orbit work?
An orbit is a path around another object in space. A planet is already moving. The Sun’s gravity pulls it inward and bends its path. Press Play to watch. Then try Slow down or Speed up.
Green: the way it is movingGold: the Sun’s pull, always inward
A circle around the Sun · 29.8 km/s
Earth’s distance. Green is the way the planet is already going. Gold is the pull, always straight at the Sun. They stay at right angles, so the pull turns the planet instead of speeding it up. Press Slow down — the other side of the path is what moves.
What to look for
The gold arrow points toward the Sun. It shows the pull of gravity. The green arrow shows the direction the planet is moving.
Press Slow down once. How does the path change? Press Speed up and compare. The dashed circle helps you see the change.
Questions answered
Does gravity push the planet forward? No. It pulls toward the Sun. That pull changes the planet’s motion.
What is an ellipse? It is a closed oval. The Sun sits away from the middle of the oval. Explore how changing speed changes the path.
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Speed and distance
For a circular orbit at Earth’s distance, the speed is about 30 kilometres per second. A slower start makes the path dip inward. A faster start makes it reach farther out. Enough speed lets the object escape instead of returning.