# Gravity barrier?

1. Jul 20, 2006

### shelpdogg

gravity barrier??

Hello all.....first post
I have a question about a "gravity barrier" that exists.

I was in a discussion about the space shuttle launch that took place a few weeks ago and somehow we got on the subject of a gravitational barrier. Meaning the shuttle had to break at 4000 mph for it to have enough velocity to carry itself into space....kinda like a slingshot.

Is this true....can someone explain a bit more in detail??

Sorry....I'm a tard when it comes to physics....

2. Jul 20, 2006

### shelpdogg

for example....

I would think the opposite...
If something is falling at a certain speed in which gravity makes it fall, such as a roller coaster, breaking the barrier would require propulsion of some sort to push it past the point in which gravity makes it move.

Am I on the right track?

Last edited: Jul 20, 2006
3. Jul 20, 2006

### ZapperZ

Staff Emeritus
Look up something known as the 'escape velocity'.

http://hyperphysics.phy-astr.gsu.edu/hbase/vesc.html

This is valid under the most simplest condition without including other external factors such as air resistance and earth's rotation.

Zz.

4. Jul 20, 2006

### shelpdogg

so basically.....what I get out of this is;
escape velocity - says that kinetic energy is equal to gravitational potential energy...without any other factors such as wind resistance?

In this case, the object does have resistance.
Does the gravity barrier idea even apply?

5. Jul 20, 2006

### ZapperZ

Staff Emeritus
Think about it. This is the minimum velocity needed to escape without any other factors. So if you add air resistance, do you think you would need a larger or smaller escape velocity?

Zz.

6. Jul 20, 2006

### pervect

Staff Emeritus
The space shuttle needs a certain velocity to reach orbit. That's the real point.

I think the idea of a "gravity barrier" is simply some popularists misguided idea to make the idea that the space shuttle needs a certain velocity to reach orbit "simpler". Don't take it too literally, or your brain will turn to sludge :-).

7. Jul 20, 2006

### shelpdogg

I had never heard of this sort of thing...that is why I thought to ask the experts in the field. As far as my brain turning to mush over this....too late.

I like this forum....hope you don't mind if I drop by every now and then to ask dumb questions.:tongue:

Thanks again,
Mike

8. Jul 21, 2006

### jasc15

Air resistance wouldnt require a larger escape velocity, but it does require more power to reach it.

9. Jul 21, 2006

### Hootenanny

Staff Emeritus
Look up the definition of escape velocity, I'm sure the word 'unpowered' (or something similar) appears in there at some point . The original question is kind of moot anyway since the escape velocity only consider the force exerted by the field.

Last edited: Jul 21, 2006