Thread: Question: could one jump off the moon?

I am not sure what the gravitational pull from the moon is. Can anyone tell me if you could escape the moon's gravity merely by jumping? If not, what outside force (springs, explosion, etc.) could make you "fall" off the moon?

I am writing a blog post for my blog about the future: the moon is populated and there is a contest that whowever jumps (or "helped" jumps) the highest wins a gigantic prize. But if you over-jump you are lost in outer space and as there are tens of thousands of people in the contest, they can't recover all the "over" jumpers. Apparently people are willing to take that chance...

I want to get the facts right for this post.

My blog is here, to give you an idea of the format: http://futurefeeds.blogspot.com/ ... or just for your entertainment.

Thanks in advance...

i'm sure you couldn't jump off the moon
one of the moonwalkers once hit a golf ball on the moon, and even that didn't achieve escape velocity

you might be in danger of jumping off on one of the smaller asteroids (in the order of 10miles across or less), but if memory serves me right, the moon still has 1/6th the gravity of the earth

in order to escape it, you need about the same power as Apollo's LEM used

I've heard that if you were standing on Mars' moon Phobos and got a really good jump you could potentially get into orbit around it. Of course it's only 15km across and our moon is about 10^8 times more massive, so no, you wouldn't be able to jump off it. marnixR gave a perfect example of the thrust required to break out of orbit. Those rockets on the Apollo moon landers are pretty good sized.

So many fun facts on wiki...
escape velocity for Phobos: 11m/s
escape velocity for Deimos: 6.9m/s
escape velocity for the Moon: 2380m/s
average human jumping velocity: about 2.5m/s

escape velocity for Phobos: 11m/s
escape velocity for Deimos: 6.9m/s
escape velocity for the Moon: 2380m/s
average human jumping velocity: about 2.5m/s

Good to know.

Originally Posted by Feifer

So many fun facts on wiki...
escape velocity for Phobos: 11m/s
escape velocity for Deimos: 6.9m/s
escape velocity for the Moon: 2380m/s
average human jumping velocity: about 2.5m/s

Thanks all, this is really helpful, so I guess I should have something that will have to shoot me up at a speed of more than 2km/s. Maybe I should go for a smaller moon. What reason could people have to go to Deimos or Phobos, any minerals to be mined there? (I'll take a look at Wikipedia, but any suggestions are welcome)

how about one of the earth orbit crossing asteroids like Eros ? the main reason being that it would be easier to achieve than going all the way to Mars + the rationale being that you might want to investigate how you're going to prevent them from colliding them with the earth should one be on a collision course

Originally Posted by marnixR

how about one of the earth orbit crossing asteroids like Eros ? the main reason being that it would be easier to achieve than going all the way to Mars + the rationale being that you might want to investigate how you're going to prevent them from colliding them with the earth should one be on a collision course

Thanks for the suggestion. Are you talking about this one: 433 Eros? I know it comes near Earth. Why would they (people, I assume) collide with Earth? Is it because if they jump off, they will be pulled into the Earth's gravitional field? That is even better for my story than just falling off...

Right now nasa is trying to cataloging all the near earth objects over 1km in diameter. Each one of these, like eros, during their orbit around the sun cross a point in the orbit of the earth. If the earth happens to be in the way during the crossing.. bam, you got a collision with potentially devastating global consequences. If we ever find one of these NEOs through orbit projection that will eventually collide, it's obviously in our best interest to figure out how to push it out of the way, hence going to eros and doing a little preemptive experimentation.

Just to clarify for TicoSox, pretty sure marnixR was implying that Eros might collide with Earth, not the lunatics jumping off of it - although jumping from the surface of an Asteroid and landing on Earth would be quite an impressive tale for the grandkids.

Originally Posted by syntheticlight

Just to clarify for TicoSox, pretty sure marnixR was implying that Eros might collide with Earth, not the lunatics jumping off of it - although jumping from the surface of an Asteroid and landing on Earth would be quite an impressive tale for the grandkids.

Thanks for the clarification. I may still use it one way or another in my story. But it seems like jumping from the moon by individuals with individually powered devices is a bit far-fetched, although it would be a cool contest trying to get the highest without leaving the Moon's gravity in some rocket powere pack/suit. I am not sure the human body would take those kinds of excessive forces, though.

Originally Posted by Feifer

So many fun facts on wiki...
escape velocity for Phobos: 11m/s
escape velocity for Deimos: 6.9m/s
escape velocity for the Moon: 2380m/s
average human jumping velocity: about 2.5m/s

Yes but the 2.5m/sec fgure is for here on earth. On Phobos you would probably only 'weigh' a few hundred grams which may mean you could achieve escape velocity especially if you 'jumped' using your hands rather than your feet (think about it..).



Tricosox,

It does not matter how high you jump on earth from a standing start, you'll land with the same velocity you jumped with (provided you land at the same altitude you took off from) so there should not be a problem with forces (unless you were propelled with assistance).

oh yeah... you're totally right. When you weigh only a little more than half a newton, the velocity you would be able to jump with would basically be however fast you could go from squatting to standing in zero g.

Originally Posted by Megabrain

Yes but the 2.5m/sec fgure is for here on earth. On Phobos you would probably only 'weigh' a few hundred grams which may mean you could achieve escape velocity especially if you 'jumped' using your hands rather than your feet (think about it..).



Tricosox,

It does not matter how high you jump on earth from a standing start, you'll land with the same velocity you jumped with (provided you land at the same altitude you took off from) so there should not be a problem with forces (unless you were propelled with assistance).

Aha, the plot thickens. So Phobos would work is what you are saying, but the moon is still too big to jump off?

Thanks, you guys are awesome!

Originally Posted by Megabrain

Originally Posted by Feifer

So many fun facts on wiki...
escape velocity for Phobos: 11m/s
escape velocity for Deimos: 6.9m/s
escape velocity for the Moon: 2380m/s
average human jumping velocity: about 2.5m/s

Yes but the 2.5m/sec fgure is for here on earth. On Phobos you would probably only 'weigh' a few hundred grams which may mean you could achieve escape velocity especially if you 'jumped' using your hands rather than your feet (think about it..)

It would be nice to know where the 2.5 m/s figure comes. It could be acceleration (2.5 m/s^2) and then you would be stuck as you can't free yourself from your mass. :wink:

Anyway the whole idea of jumping of the moon is nonsense. Either you know how much thrust you have (and that would be the case if you used rocket engines) or you don't (like, if you jumped on your leg's force), but your legs will never take you very far on the moon. If you're not afraid of plagiarism, you could make a story about holding a extreme race on the moon and how the thing goes wrong for some runners as they begin to get frozen feet for continuously stepping on regolite (at some -160º C) with too light footwear. (Idea by Arthur C. Clarke on The Hammer of God)

Ohh... and please move your schedules back, way back. Some of your dates screech as they're too soon. FAI, 2012 is 5 years from now. Think, what we got now that wasn't pefectly foreseable or already existed in 2002...? :wink:

(Your moon story of big reward for desperate sportmen implies some sort of functional, thriving colonisation on Moon... and that means 2150 at least, specially provided how are space budgets in this sorrow days. Think of how long it was the road from the Mary Rose to the Declaration of Independence... and it happened on an already civilized land, not a human-less barren! Science Fiction, unlike what Hollywood thinks, it's a complicated matter that requires a thorough knowledge of whatever you're talking about...) 8)

I agree, this story would have to take place much later. On the other hand, who would have predicted that when V2's were hitting London that men would have landed on the moon 25 years later? But as you can tell my "Future Feeds" can come from any time in the future. Also agree with the colonisation, that was to be part of the story.

But how about the suggestions earlier about Phobos (if it were to be colonized) and jumping off (lef-powered or rocket powered)?

Yeah, I agree with putting it somewhere closer than 2150 maybe, but at the same time 2150 isn't too late either.

Originally Posted by TicoSox

Originally Posted by syntheticlight

Just to clarify for TicoSox, pretty sure marnixR was implying that Eros might collide with Earth, not the lunatics jumping off of it - although jumping from the surface of an Asteroid and landing on Earth would be quite an impressive tale for the grandkids.

Thanks for the clarification. I may still use it one way or another in my story. But it seems like jumping from the moon by individuals with individually powered devices is a bit far-fetched, although it would be a cool contest trying to get the highest without leaving the Moon's gravity in some rocket powere pack/suit. I am not sure the human body would take those kinds of excessive forces, though.

The retina's of a person's eyes become detached at 4 G's. (so less than 40 meters per second per second is about the maximum acceleration the human body can withstand. )

As for squatting and jumping in zero G, inertial forces still have to be taken into account, so you could still only jump so high or fast. Think of somebody laying their stomach on a skate board on a flat surface and then pushing off of a wall with their legs. Whatever speed you could get on the skateboard is approximately the maximum speed a person can jump at in zero G.

Originally Posted by Lucifer

It would be nice to know where the 2.5 m/s figure comes. It could be acceleration (2.5 m/s^2) and then you would be stuck as you can't free yourself from your mass. :wink:

I actually got this figure from a google books search on human body mechanics. It gave the y component of velocity (not acceleration) of a long jumper. I was assuming it was taken the moment the feet leave the ground because at that point there is no more acceleration from the legs and gravity has yet to have an effect. It ultimately turned out to be a moot point because as megabrain pointed out the legs are trying to overpower gravity here on earth, not on another celestial body.

Originally Posted by Feifer

Originally Posted by Lucifer

It would be nice to know where the 2.5 m/s figure comes. It could be acceleration (2.5 m/s^2) and then you would be stuck as you can't free yourself from your mass. :wink:

I actually got this figure from a google books search on human body mechanics. It gave the y component of velocity (not acceleration) of a long jumper. I was assuming it was taken the moment the feet leave the ground because at that point there is no more acceleration from the legs and gravity has yet to have an effect. It ultimately turned out to be a moot point because as megabrain pointed out the legs are trying to overpower gravity here on earth, not on another celestial body.

Though it might be possible, given the old 'rule of thumb' that the max power output for a human is approximately 0.5 hp (sorry for the old units), to calculate velocity at lift off (making assumptions regarding mass of human and length of legs/of spring). Anyone?

Originally Posted by TicoSox

I am not sure what the gravitational pull from the moon is. Can anyone tell me if you could escape the moon's gravity merely by jumping? If not, what outside force (springs, explosion, etc.) could make you "fall" off the moon?

I am writing a blog post for my blog about the future: the moon is populated and there is a contest that whowever jumps (or "helped" jumps) the highest wins a gigantic prize. But if you over-jump you are lost in outer space and as there are tens of thousands of people in the contest, they can't recover all the "over" jumpers. Apparently people are willing to take that chance...

I want to get the facts right for this post.

My blog is here, to give you an idea of the format: http://futurefeeds.blogspot.com/ ... or just for your entertainment.

Thanks in advance...

I am very grateful for all your comments. I didn't think it would it be that hard a question and that some knowledge of Newtonian physics (which is hidden away somewhere deep in my memory, alas) could easily answer it. But there are a lot uf unknown variables. How do the muscles work in lower than Earth gravity? For now I am thinking of letting this jumping contest take place on Phobos with Mars being colonized for a long, long time. The jumping contest is after all a long, established tradition on Mars...

Originally Posted by Feifer

So many fun facts on wiki...
escape velocity for Phobos: 11m/s
escape velocity for Deimos: 6.9m/s
escape velocity for the Moon: 2380m/s
average human jumping velocity: about 2.5m/s

Hmmm.....what would happen if you were to cough or fart or something........how fast does the gas come out, does anyone know ? - im sure that might work ?

And here I thought I was trying my best to avoid absurdities. :wink: But yes, fart propulsion, why not?

Well a sneeze can come out of you at 100mph but I don't think it would do much since the mass of the air getting sneezed out is so much smaller than the mass of a human body. I'm looking at it like a conservation of momentum problem where the velocity of the body = (velocity of the sneeze x mass of the air)/mass of the body. Of course when all the thrust is coming out of one side of your head, the most it would do is slowly make you rotate.

ps. This thread is getting ridiculous ...but still fun

Found this link on another thread, I guess you would need some external power source to get of Deimos or Phobos, but it seems within reasonable limits, not needing crazy amounts of G-forces...
http://space.newscientist.com/articl...r-mankind.html

Thank you all for you valuable feedback and comments. I have learned a lot, and my article has become a lot more "scientific" than if I would not have posted this subject. Here is the final article: http://futurefeeds.blogspot.com/2007...leaves_15.html