Gravitational Field Surface

1m diameter rubber sheet acts as curved space for ball bearing masses.

What it shows:

In general relativity, gravity is replaced by a curved space geometry, where the curvature is determined by the presence and distribution of matter. Objects move in straight lines, or along geodesics, but because of the curvature of space, their paths will simulate the effect of gravitational attraction. This demo gives a two dimensional view of warped space.

How it works:

In this 2-D analog, a 1 meter diameter piece of dental dam forms a sheet that represents the geometry of space. The sheet is sandwiched between two wooden hoops that act as a frame to keep things taught (see figure 1). Use a massive ball bearing (say 500g) as a stationary central object, smaller ball bearings can be rolled in its field. You can show clearly circular, elliptical or parabolic orbits in this way.

figure 1. The dental dam elastic surface, shown distorted by a ball bearing mass.

gravitational field surface

Setting it up:

Place the frame so that it is supported a reasonable distance off the ground, with the area under the sheet open so that it warps without obstruction. Resting on two chairs will do.


The dental dam does degrade over time, so test the setup before the class. Make sure the sheet can take the heaviest ball bearing, or you’ll be creating a singularity demo!