How do train wheels keep from over heating when the train is going down the tracks?
I would take exception with the other responses to your question. The cause of gravity is unknown. Gravity also has nothing to do with electromagnetism. We can predict gravitational attraction of an object by its mass but there is no unification, or theory, that binds mass with gravitational force. Theoretically the Higgs Boson and interaction with the Higgs Field endows bodies with mass but not gravity. It is theorized that gravity causes a distortion in a hypothetical space-time continuum, but that doesn't offer a theory for the cause of gravitational force.
Gloves - Goggles - Tie hair back - Pull sleeves back - No running with scissors :)
More proof that liberalism is a mental disorder.
