kendalls
have plotted distributions of the orbital radii of the asteroids
A gap is located at an average orbital distance, and asteroid orbits often have large eccentricities. Edit: These are the "Kirkwood gaps" and they are caused by the effect of Jupiter's gravity on the asteroids. I've not deleted the previous answer, but I don't think it helps much. The gaps are in the distribution of the values of the semi-major axes of the orbits of asteroids rather than particular places in space. So orbital eccentricities can't be the explanation. I think it's simply because asteroids stray into the Kirkwood gaps under various gravitational forces. But these orbits are not stable and asteroids will tend to be cleared away again, eventually.
a crevace
The battlements themselves are known as crenellations and the gaps within them are known as crenels or embrasures. Please see the related links.
There are thousand of gaps in Saturn's rings - the main ones are called Cassini Division and Encke Gap
Orbital resonances with Jupiter
An asteroid can get out of the belt because of another huge asteroid hitting it or by getting pulled into an unstable orbit by the gravity of Jupiter. There are gaps called Kirkwood gaps in the asteroid belt at certain distances from the sun because the influence of Jupiter causes orbits at those distances to become unstable. A collision with a comet would be another possible reason, but this is very unlikely (except in Hollywood movies).
I believe its because Asteroids typically cluster together and this creates "gaps" on the sky, but don't quote me on this.
the period of an orbiting asteroid would be a simple fraction (like 1/3 or 1/4) of Jupiter's orbital period.
have plotted distributions of the orbital radii of the asteroids
A gap is located at an average orbital distance, and asteroid orbits often have large eccentricities. Edit: These are the "Kirkwood gaps" and they are caused by the effect of Jupiter's gravity on the asteroids. I've not deleted the previous answer, but I don't think it helps much. The gaps are in the distribution of the values of the semi-major axes of the orbits of asteroids rather than particular places in space. So orbital eccentricities can't be the explanation. I think it's simply because asteroids stray into the Kirkwood gaps under various gravitational forces. But these orbits are not stable and asteroids will tend to be cleared away again, eventually.
Gaps in rock layers are called unconformities.
Gaps that are now called kirkwood gaps
Lubrication is filling in gaps using oil.
Before it breaks. Check the Belt for age/wear by feeling it for gaps on the underside (drive side). If there are good sized gaps in the tread, REPLACE THE BELT. If it's heavily glazed on the TOP, REPLACE IT. It's a cheap replace instead of an Engine rebuild.
Perception is when you fill in the gaps with what your senses tell you.
They are called uncomformities.