Max's Gravity Well

What you'll learn

• That gravity is what mass does to space, not something space has on its own
• Why heavier things make a deeper dent and pull harder
• That an orbit is just falling sideways fast enough to keep missing
• Why the inner planets race around and the outer ones crawl
• That a hammer and a feather fall at the same speed when there is no air

How to play

1. Drag the funnel to spin it, and scroll or pinch to zoom in and out.
2. Slide the Sun's mass up and down and watch the funnel get deeper or shallower.
3. Press Turn gravity off and watch every planet fly away in a straight line.
4. Switch to Throw a comet, drag on the sheet to aim, and let go.

FAQ

What age is this for?

Around 7 and up. Younger children love spinning the funnel and switching gravity off; older ones can dig into orbital speeds, escape velocity and the inverse square law in the readout.

Is the funnel real, or just a picture?

It is worked out live. The depth at every point on the grid is calculated from the mass and position of every body on the sheet, sixty times a second, so the dents really do move with the planets.

Is space really a rubber sheet?

Not literally — real space is bent in three dimensions, not two, so nobody can draw it properly. The sheet is the picture physicists use to think about it, and it gets the important part right: mass bends space, and bent space is what we feel as gravity.

Do I need to install anything?

No. It runs in any web browser, it is free, and there is no signup.