Orbits & Gravity: The Dance of Planets
Why planets fall without ever hitting the ground
Why planets fall without ever hitting the ground
Every object with mass pulls on every other object. The more massive the object, the stronger its pull. The farther away, the weaker. This is gravity, and it governs every orbit in the universe.
Move your mouse to place a test mass. Watch how the gravitational pull changes with distance.
You are gravitationally attracted to your phone right now. The force is just unimaginably tiny compared to Earth's pull on you.
An orbit happens when an object moves sideways fast enough that it keeps falling toward a body but always misses. Too slow and it crashes. Too fast and it escapes. Adjust the launch velocity to find the sweet spot.
The International Space Station orbits Earth at about 7.66 km/s. At that speed you could fly from New York to London in under 12 minutes.
In the 1600s, Johannes Kepler discovered three rules that describe how every planet moves. Click each law to see it in action.
Planets orbit in ellipses, not perfect circles. The Sun sits at one focus of the ellipse.
A line from the Sun to a planet sweeps equal areas in equal times. Planets speed up when closer.
Farther planets take longer to orbit. The period squared is proportional to the distance cubed.
Eight planets, each held in orbit by the Sun's gravity. Click a planet to see its orbital details.
If the Sun were a basketball, Earth would be the size of a peppercorn about 26 meters away. Jupiter would be a walnut at 135 meters.
You've explored the invisible force that keeps planets in orbit, moons circling, and galaxies spinning. The same gravity holding you to the ground shapes the entire universe.
Gravity pulls everything toward everything else. It weakens with distance but never reaches zero.
An orbit is just falling toward a body and constantly missing. Speed sideways balances the pull inward.
Planets trace ellipses with the Sun at one focus. They sweep equal areas in equal times, speeding up when close.
Go fast enough and gravity can never pull you back. For Earth, that is about 11.2 km/s.
Put your new knowledge into practice!