Picture yourself on the surface of the Earth (or in a boat on a river). Now, if you were to toss something up into the air, it would eventually be pulled back down, due to the effects of gravity. Obviously, this force is not indomitable, as we've escaped the Earth's gravitational well many a time (most recently, when we sent something awesome to Mars—because orbit doesn't really count as escaping the Earth's gravity). In fact, if you were to toss something up with enough force, it would fly away forever, never to be seen again. The speed you instantaneously imparted on that object when you threw it is the Earth's escape velocity. Now, let's say we increase the mass of the Earth to that of Jupiter, but keep the size the same (we make the Earth much, much more dense). Now, in the instant before you were liquified by it, you'd notice the gravity has become much, much stronger than it was. This makes perfect sense, as gravity is a property of mass.