---
title: Falling around the world
description: Launch a satellite, follow the forces, and discover what makes an orbit.
---

[@orbit]: ./orbit.components.md
[@styles]: ./orbit.css

# Falling around the world

**An orbital playground · Three experiments · About five minutes**

An orbit is a fall that keeps missing the ground. Find out what that means
by launching a satellite of your own. Drag the scene to look around, or choose
**Follow satellite** to travel beside it. **Top-down** gives you a diagram view.

[@link.play Explore orbits](./orbit.demo.md)

---

## Can you make it stay up?

Your satellite starts one planet radius above the surface. Give it some
sideways speed, then **Launch**. What happens if you launch too slowly?

<orbit-lab id="first-launch" altitude="1" speed="0.4">
  Adjust launch speed, or choose Top-down and drag upward from the satellite. Try to complete
  one revolution without touching the planet.
</orbit-lab>

A trail records where you have been. **Reset** gives you another attempt.
Try a little more speed each time. What changes about the shape of the trail?

---

## Falling—and missing

This satellite starts at the speed for a circular orbit. Before launching,
predict where the two arrows will point a quarter of the way around.

<orbit-lab id="follow-the-forces" altitude="1" speed="0.707" vectors="on">
  Launch, pause, then use **Step**. The gold arrow shows velocity; the blue
  arrow shows gravitational acceleration. Their lengths use different scales.
</orbit-lab>

Velocity points along the path. Gravity points inward, continually bending
that path. At circular speed, the satellite keeps falling while its distance
from the center stays constant. There is still gravity in orbit.

---

## Find your own orbit

This launch starts farther from the planet. Predict: does a circular orbit
here need **more or less speed**? Test your prediction, then turn on the
predicted path to see how a small change reshapes the orbit.

<orbit-lab id="find-an-orbit" altitude="2" speed="0.707" vectors="on">
  Find a nearly circular orbit. Watch the distance readout: how little can
  you make it vary over a full revolution?
</orbit-lab>

In our units, circular speed is **1 / √r**, where *r* is distance from the
planet’s center. Here *r* is 3, so try about **0.577**. A higher circular orbit
needs less speed, and takes longer to complete.

---

## Open the observatory

These experiments use an idealized model: one spherical planet, a satellite
with negligible mass, no atmosphere, and motion in a single plane. Distances
use the planet’s radius; time and speed use consistent simulation units.
The gold path is a numerical prediction using the same gravity model.

Change the lesson by editing `altitude`, `speed`, or `vectors` on an
`<orbit-lab>` tag. Keep your question and experiment together in a Block.
The [literate component source](./orbit.components.md) explains the controls,
rendering, and physics, with an experiment you can run.

<x-docs-source-link />