Weather satellites
Satellites repeatedly pass over Earth and observe clouds, storms, and temperature.
Key idea: the right sideways speed sustains orbitLabs / Physics / Orbits & Gravity
Orbits & Gravity
Launch a planet and discover why it can circle a star instead of falling straight into it.
Why it matters
Where do we use this?
Orbits let satellites provide maps, weather forecasts, communication, and science. The same ideas explain moons, planets, comets, and spacecraft.
Navigation
Positioning satellites follow known orbits so receivers can calculate where they are.
Key idea: predictable paths enable locationSpace missions
Engineers adjust speed to enter orbit, move between orbits, or escape a planet.
Key idea: small speed changes reshape pathsUnderstanding the Solar System
Gravity explains the paths of planets, moons, asteroids, and comets.
Key idea: one rule creates many orbit shapesOur driving questionHow can something keep falling without hitting the star?
Explore
Try it first
Drag and release to launch a planet. Try different speeds, directions, and star masses.
speed —distance —planets 0
Notice: gravity always pulls toward the star, while sideways motion keeps carrying the planet past it.
Investigate
Three guided experiments
Make a prediction before touching the controls. Then test it and explain the evidence in your own words.
Procedure
- Launch a planet almost directly at the star.
- Clear it and launch another mostly sideways.
- Compare the paths.
Record
Describe which launch avoids the star.
Explain
What is happening?
Gravity turns
Gravity pulls toward the star, continuously changing the direction of motion.
Speed carries
Sideways speed carries the planet forward while it falls inward.
Balance shapes the path
Different combinations of speed and gravity create circles, ellipses, crashes, or escapes.
Circular orbit speed
v = √(GM / r)- M
- mass of the star
- r
- distance from its centre
- G
- gravity constant
Worked example
Farther planets need less speed for a circular orbit, but they travel a much larger path and take longer to go around.
Check your model
Can you predict the pendulum?
Extend
Take it further
Create the most circular orbit you can. Then change only one setting and explain why the new path is no longer circular.