# Gravitational pull of Earth and escape velocity

1. Oct 28, 2015

### Zynoakib

I know once the escape velocity is reached, the object will continuous to move away from the Earth. But the Earth's gravity can still act on the object no matter how far it goes, so what keeps the object from stopping or even returning back to Earth?

2. Oct 28, 2015

### phinds

It is inherent in the equations of motion. The object does slow down some but not down to zero. That's really the definition of escape velocity; giving an object sufficient velocity that gravity never quite overcomes it. Mathematically, when it gets to infinity it has zero velocity relative to the Earth (assuming it left with exactly the escape velocity), but of course in reality it will be more affected by celestial bodies other than the Earth WAY long before then (and the infinite "then" never actually occurs in reality)

3. Oct 29, 2015

### Zynoakib

Just want to explain it in my own wording

Although the earth's gravity can still attract the object to slow it down no matter how far it goes, it will take forever for the object to be slowed down just by a slight degree.

4. Oct 29, 2015

### phinds

No, that's not a good way to say it. It will take forever for it to be slowed to zero.

5. Oct 29, 2015

### Staff: Mentor

So, note that escape velocity is not a single/constant value. It decreases with distance. So an object that is launched exactly at escape velocity will always be slowing down, and will always be at the escape velocity of whatever distance it is at.

6. Oct 29, 2015

### phinds

Agreed for sure.

7. Oct 29, 2015

### tfr000

"Hyperbolic excess velocity" is what you're looking for here.

8. Oct 30, 2015

### Zynoakib

Thanks guys, now I understand