# Why can't you get past the Earth's atmoshere slowly? **URL:** \ **Category:** Factual Questions\ **Created:** [December 18, 2002, 1:56am UTC](https://boards.straightdope.com/t/why-cant-you-get-past-the-earths-atmoshere-slowly/143464 "2002-12-18T01:56:06Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![x-ray\_vision](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/x-ray_vision/32/351_2.png) [@x-ray\_vision](https://boards.straightdope.com/u/x-ray_vision)\ **Post date:** [December 18, 2002, 1:56am UTC](https://boards.straightdope.com/t/why-cant-you-get-past-the-earths-atmoshere-slowly/143464/1 "2002-12-18T01:56:06Z")
I was watching JEOPARDY! tonight, and the final jeopardy answer was something like: 24,527 (or close to that) mph is needed to achieve this. The correct question was something like: What speed do you need to achieve to escape the Earth’s atmosphere? Why can’t you keep going up at a slower speed? At what point will you stop going up if you’re going slower than that? What is the force that stops you from going up? ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [December 18, 2002, 2:02am UTC](https://boards.straightdope.com/t/why-cant-you-get-past-the-earths-atmoshere-slowly/143464/2 "2002-12-18T02:02:50Z")
The question was most likely worded slightly incorrectly. In order to escape the gravitational pull of a planet, you need to achieve the _escape velocity_. For earth, that’s about 25,000 miles per hour. If you achieve a velocity lower than that, you will fall down or get stuck in orbit. > [@](#): > > Why can’t you keep going up at a slower speed? At what point will you stop going up if you’re going slower than that? What is the force that stops you from going up? You can continue to push upwards with all your might. However, eventually you will run out of fuel, or whatever energy source is powering your vehicle. At that point, you’ll fall, unless you’ve reached escape velocity. ---
**Author:** ![x-ray\_vision](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/x-ray_vision/32/351_2.png) [@x-ray\_vision](https://boards.straightdope.com/u/x-ray_vision)\ **Post date:** [December 18, 2002, 2:07am UTC](https://boards.straightdope.com/t/why-cant-you-get-past-the-earths-atmoshere-slowly/143464/3 "2002-12-18T02:07:38Z")
I remember reading in this forum that you need a sideways force to get stuck in orbit, so I don’t think you would end up in orbit. What force would stop you from continung to go up? It can’t be gravity. That would already be weaker since you are already farther from the Earth. ---
**Author:** ![Achernar](https://avatars.discourse-cdn.com/v4/letter/a/e274bd/32.png) [@Achernar](https://boards.straightdope.com/u/Achernar)\ **Post date:** [December 18, 2002, 2:08am UTC](https://boards.straightdope.com/t/why-cant-you-get-past-the-earths-atmoshere-slowly/143464/4 "2002-12-18T02:08:14Z")
You’re right, that you can go as slow as you want, but it’s more fuel-efficient to burn all your fuel early on, and get up to the escape speed. So, in practice, anything that goes into space does this. ---
**Author:** ![SandWriter](https://avatars.discourse-cdn.com/v4/letter/s/8491ac/32.png) [@SandWriter](https://boards.straightdope.com/u/SandWriter)\ **Post date:** [December 18, 2002, 2:08am UTC](https://boards.straightdope.com/t/why-cant-you-get-past-the-earths-atmoshere-slowly/143464/5 "2002-12-18T02:08:55Z")
IANARS, but IIRC, you need to defeat gravity to escape the earth’s atmosphere. If you go any slower, the Earth’s Gravity will cause you to go into orbit instead of escaping into space? Chronos will jump in here and explain it all. ---
**Author:** ![sigSEGV](https://avatars.discourse-cdn.com/v4/letter/s/b5a626/32.png) [@sigSEGV](https://boards.straightdope.com/u/sigSEGV)\ **Post date:** [December 18, 2002, 2:11am UTC](https://boards.straightdope.com/t/why-cant-you-get-past-the-earths-atmoshere-slowly/143464/6 "2002-12-18T02:11:45Z")
IIRC, 25,000 mph is the speed tangential to the earth’s surface that is needed so that the rate you fall due to gravity equals the rate that the earth curves away from you. There is nothing stopping us from from going 5 miles per hour straight up until we exit the atmosphere – it would just be very inefficient. ---
**Author:** ![x-ray\_vision](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/x-ray_vision/32/351_2.png) [@x-ray\_vision](https://boards.straightdope.com/u/x-ray_vision)\ **Post date:** [December 18, 2002, 2:14am UTC](https://boards.straightdope.com/t/why-cant-you-get-past-the-earths-atmoshere-slowly/143464/7 "2002-12-18T02:14:32Z")
ok, I can see why 5mph would be inefficient, but why not 20,000mph? ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [December 18, 2002, 2:14am UTC](https://boards.straightdope.com/t/why-cant-you-get-past-the-earths-atmoshere-slowly/143464/8 "2002-12-18T02:14:56Z")
I think the question is completely wrong. Escape speed has nothing to do with the atmosphere. As **friedo** said, if something is moving below escape speed, eventually gravity will pull it back down to earth. If something is moving faster than escape speed, inertia will keep it moving away from the earth forever. It only applies to inert projectiles. If you have an engine, in theory you can keep it running forever and gradually move away from the earth at 1mph. It’s still an important number because most spacecraft behave like inert projectiles. If you want to launch an interplanetary probe, you put it in orbit around earth and then use a rocket engine to give it a good kick, bringing the speed above escape speed. Then the spacecraft will coast all the way to the destination, where you use your engine again to stop. It also happens to be a very energy-efficient method. ---
**Author:** ![MC\_Master\_of\_Ceremonies](https://avatars.discourse-cdn.com/v4/letter/m/bb73d2/32.png) [@MC\_Master\_of\_Ceremonies](https://boards.straightdope.com/u/MC_Master_of_Ceremonies)\ **Post date:** [December 18, 2002, 2:16am UTC](https://boards.straightdope.com/t/why-cant-you-get-past-the-earths-atmoshere-slowly/143464/9 "2002-12-18T02:16:56Z")
In reality I doubt the space rockets actually achieve 25,000 mph, because the further away you get from the earth the lower the escape velocity (from the earth) ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [December 18, 2002, 2:17am UTC](https://boards.straightdope.com/t/why-cant-you-get-past-the-earths-atmoshere-slowly/143464/10 "2002-12-18T02:17:34Z")
> [@](#): > > There is nothing stopping us from from going 5 miles per hour straight up until we exit the atmosphere – it would just be very inefficient. No, you can’t get out of the earth’s atmosphere by going 5mph continuously. The force of gravity causes an object to accelerate downwards (on earth, at 9.8m/s[sup]2[/sup]). The longer your vehicle is off the ground, the more it accelerates downward. Thus, in order to maintain a constant velocity of 5mph, you have to continuously apply more and more fuel. You would eventually need an infinite amount of fuel to keep going. ---
**Author:** ![MC\_Master\_of\_Ceremonies](https://avatars.discourse-cdn.com/v4/letter/m/bb73d2/32.png) [@MC\_Master\_of\_Ceremonies](https://boards.straightdope.com/u/MC_Master_of_Ceremonies)\ **Post date:** [December 18, 2002, 2:18am UTC](https://boards.straightdope.com/t/why-cant-you-get-past-the-earths-atmoshere-slowly/143464/11 "2002-12-18T02:18:22Z")
The easiest way to look at it is, if you want to throw a baseball into out of space you need to throw it at 25,000 mph. ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [December 18, 2002, 2:19am UTC](https://boards.straightdope.com/t/why-cant-you-get-past-the-earths-atmoshere-slowly/143464/12 "2002-12-18T02:19:28Z")
Now that I just read what I post, I’m not sure if that’s right. My memory of physics is playing tricks on me tonight. Am I talking out of my ass today? 🙂 ---
**Author:** ![MC\_Master\_of\_Ceremonies](https://avatars.discourse-cdn.com/v4/letter/m/bb73d2/32.png) [@MC\_Master\_of\_Ceremonies](https://boards.straightdope.com/u/MC_Master_of_Ceremonies)\ **Post date:** [December 18, 2002, 2:21am UTC](https://boards.straightdope.com/t/why-cant-you-get-past-the-earths-atmoshere-slowly/143464/13 "2002-12-18T02:21:11Z")
Well sorta, 5mph isn’t a very efficent speed for a space rocket but you don’t need infinite fuel! ---
**Author:** ![x-ray\_vision](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/x-ray_vision/32/351_2.png) [@x-ray\_vision](https://boards.straightdope.com/u/x-ray_vision)\ **Post date:** [December 18, 2002, 2:24am UTC](https://boards.straightdope.com/t/why-cant-you-get-past-the-earths-atmoshere-slowly/143464/14 "2002-12-18T02:24:37Z")
> [@](#): > > _originally posted by **scr4** _ > > As friedo said, if something is moving below escape speed, eventually gravity will pull it back down to earth. I still don’t understand why gravity will pull it down when it is already so far from the Earth. ---
**Author:** ![sigSEGV](https://avatars.discourse-cdn.com/v4/letter/s/b5a626/32.png) [@sigSEGV](https://boards.straightdope.com/u/sigSEGV)\ **Post date:** [December 18, 2002, 2:26am UTC](https://boards.straightdope.com/t/why-cant-you-get-past-the-earths-atmoshere-slowly/143464/15 "2002-12-18T02:26:19Z")
> [@](#): > > \*Originally posted by friedo \* > \*\*No, you can’t get out of the earth’s atmosphere by going 5mph continuously. \*\* I don’t follow you. Where are you getting the infinite fuel thing? If you continuously travel at 5mph upwards, you would need a steadily increasing amount of thrust, but not infinite. ---
**Author:** ![Cooper](https://avatars.discourse-cdn.com/v4/letter/c/50afbb/32.png) [@Cooper](https://boards.straightdope.com/u/Cooper)\ **Post date:** [December 18, 2002, 2:30am UTC](https://boards.straightdope.com/t/why-cant-you-get-past-the-earths-atmoshere-slowly/143464/16 "2002-12-18T02:30:45Z")
Friedo your suspicions are correct. What would cause the ship to burn more fuel after flying slowly upwards? It will burn an almost constant amount of fuel to overcome friction and gravity to stay at the velocity of 5 mph away from earth (of course it will burn a little more to get to 5mph) - and will actually need slightly less fuel as the atmosphere thins and gravity exerts less force the further from earth it gets. Eventually it will escape earth’s gravity entirely. It would take a ridiculous amount of fuel to do this and may not even be within the grasp of current technology and engineering but its certainly possible. ---
**Author:** ![Achernar](https://avatars.discourse-cdn.com/v4/letter/a/e274bd/32.png) [@Achernar](https://boards.straightdope.com/u/Achernar)\ **Post date:** [December 18, 2002, 2:33am UTC](https://boards.straightdope.com/t/why-cant-you-get-past-the-earths-atmoshere-slowly/143464/17 "2002-12-18T02:33:05Z")
> [@](#): > > \*Originally posted by MC Master of Cermonies \* > In reality I doubt the space rockets actually achieve 25,000 mph, because the further away you get from the earth the lower the escape velocity (from the earth) What you say is true, but it’s not as big a difference as you might think. At the surface of the Earth, escape speed is about 25008 MPH. 100 miles up, it’s 24699 MPH. ---
**Author:** ![bbeaty](https://avatars.discourse-cdn.com/v4/letter/b/c0e974/32.png) [@bbeaty](https://boards.straightdope.com/u/bbeaty)\ **Post date:** [December 18, 2002, 2:36am UTC](https://boards.straightdope.com/t/why-cant-you-get-past-the-earths-atmoshere-slowly/143464/18 "2002-12-18T02:36:03Z")
> [@](#): > > I still don’t understand why gravity will pull it down when it is already so far from the Earth. Earth’s gravity has no end, no cutoff-distance. If you fall off a 5ft ladder, youll fall towards the Earth. But if you fall off a 5 billion mile tall ladder, you’ll also fall towards the Earth. But if you’re already moving upwards fast enough, Earth’s gravity might slow you down a bit, but it can never reverse your direction. PS, the farther you are from Earth’s center, the lower your escape velocity. If you’re already standing on the top of a 10,000 mile high ladder, then to escape from the Earth entirely you don’t have to jump upwards nearly as fast as you do when standing on the ground. ---
**Author:** ![MC\_Master\_of\_Ceremonies](https://avatars.discourse-cdn.com/v4/letter/m/bb73d2/32.png) [@MC\_Master\_of\_Ceremonies](https://boards.straightdope.com/u/MC_Master_of_Ceremonies)\ **Post date:** [December 18, 2002, 2:38am UTC](https://boards.straightdope.com/t/why-cant-you-get-past-the-earths-atmoshere-slowly/143464/19 "2002-12-18T02:38:25Z")
Yes, because IIRC gravitaional force exerted is directly proportinal to the inverse square of distance (from the centre of gravity) and 100 miles doesn’t change your distance that much from the centre of the earth. You could conceivably escape to infinity by walking up a long enough ladder. ---
**Author:** ![x-ray\_vision](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/x-ray_vision/32/351_2.png) [@x-ray\_vision](https://boards.straightdope.com/u/x-ray_vision)\ **Post date:** [December 18, 2002, 2:40am UTC](https://boards.straightdope.com/t/why-cant-you-get-past-the-earths-atmoshere-slowly/143464/20 "2002-12-18T02:40:10Z")
> [@](#): > > _originally posted by **bbeaty** _ > > PS, the farther you are from Earth’s center, the lower your escape velocity. If you’re already standing on the top of a 10,000 mile high ladder, then to escape from the Earth entirely you don’t have to jump upwards nearly as fast as you do when standing on the ground. Then at what point do you need to be going so damn fast and why? [Next page](https://boards.straightdope.com/t/why-cant-you-get-past-the-earths-atmoshere-slowly/143464.md?page=2)