The "Roche Limit" for a body like the Earth, is the minimum distance that an orbiting body of similar composition can approach before becoming ripped apart due to tidal forces. Typically, it is about 2.5 times the radius of the primary, or larger, object. For the Earth and moon, this center-to-center distance is a little under 6,000 miles. Fortunately, the moon is about 40 times farther away and is in no danger of breaking apart. Despite its distance though, Earth's tidal forces dominate its moon.