Well, I was thinking. If our earth is constantly accelerating (going faster and faster), the craters that comets make would get bigger/deeper every time a comet hits us.
Scientist can see one and predict how the impact will be. They can tell us how big the crater will be (approx) and how much damage will be caused. But if the earth was accelerating, the damage and size of crater would dramatically increase, rendering all mathematical predictions wrong.
EDIT: Sorry, forgot... There have been similar sized comets that have hit the earth over long periods of time between each other, but have caused similar sized craters. If earth was constantly getting more and more speed through acceleration, 2 of the same sized comets would make massively different craters. Meaning, the later one would make a bigger crater then the earlier one. Get it? Hope so!