…and Achernar’s most recent calculations seem to refute my 2nd point. Still pondering whether or not I agree with them. 
:sigh: Yes, I have seen balloons before. I do not consider riding a balloon to be “jumping”. The Parabounce is just a balloon with a net upward bouyancy of about 2 lbs. You are not “jumping” up , you are “floating” up and you are tethered to the ground by a 100 ft line unless you are indoors. Please read http://www.parabounce.com/press/ballooning.htm
My previous post was in response to DougC. I do not consider being lifted by a balloon with positive bouyancy to be “jumping”. The OP explicitly states the balloons must only provide bouyancy which is a fraction of the person’s weight.
It is a bit tiring trying to argue a physics problem with people who have an aversion to math and will not discuss the numbers I provided. I believe Chronos, Achernar and myself all have backgrounds in science and/or engineering and we are the only ones to have tackled any figures and pretty much agree on the conclusion. I would like to know if any of those who assert opposite views to ours (balloons rising with an acceleration greater than g, etc) has a background in the sciences and/ or engineering.
I will note that if you have an elastic connection to the balloon, either a harness or a bungee cord, then you can reach greater heights. If you lift off with a certain force and reach a height h, then with a balloon, pushing off with the same force, you’ll reach a height h × m[sub]YOU[/sub] / (m[sub]YOU[/sub] + m[sub]BALLOON[/sub] - m[sub]AIR[/sub]). This ratio could theoretically be very high indeed.
Now, if you were attached with a rigid harness, you could even do better than that. Because your feet would be able to stay in contact with the ground for longer, you can apply more force than you would under normal conditions - this is ntucker’s point #1 from a few posts up.
Can you define “net bouyancy of 2 lbs”? From looking at the video clips, I take it to mean that the person and the balloon, at rest on the ground, exert about 2 pounds downward force. You stand still, you stay planted on the ground. You crouch down and make a gentle jumping motion, and you lift off the ground and make a parabolic arc through the air which is a lot higher than you could normally jump.
Sure sounds like jumping to me. If you don’t consider this “jumping,” fine, but you’re arguing semantics, and it seems weird to act like people who do consider this “jumping” are idiots.
As for why people won’t argue with your numbers, it’s probably because nobody questions whether or not they’re calculated correctly. What people are questioning is whether or not your calculations actually take all appropriate forces into account, which tends to require a more qualitative discussion.
I don’t see this anywhere in the OP (and I’m assuming, perhaps wrongly, that by ‘fraction’, you mean ‘fairly small fraction’), but I think it likely that this is the basis of our disagreement; I have been considering a scenario where the buoyancy is equivalent to 90% or more of the weight.
No, you are wrong, the ballon provides net bouyancy. Read the article I linked to. You can float up there for an hour if you like. the point is that you adjust the bouyancy with weights to make it just a tad positive. In practice it does not make much difference: you are floating in the air. If the net force is 2lbs down or 2 lbs it is not going to make much difference except that you will very slowly end up headed which way.
No, I do not consider floating with a balloon which provides 100% bouyancy to be “jumping” and the OP doesn’t either and he very specifically said in the OP the idea was only partial bouyancy. If you consider a balloon ride where you can stay up there for an hour tethered to the ground by a long rope to be a “jump” then fine.
Ok, please tell me what forces i am not considering correctly because those who seem to have a background in science and/or engineering seem to agree with me. Please give me your analysis of what forces i am not considering correctly and show me what your numbers are when you take those forces into account.
The OP says
In other words the point is not to have 100% bouyancy but if a fraction of that would help. He thinks not and I say yes, fractional bouyancy will help provided you use the elastic cords. Then you and others come in and say even without elastic cords the balloon will help. I say that is not so and I still maintain that but the posts are moving around all the time. First someone introduces a rigid harness, now we have 100% bouyancy… The Parabounce provides 100% bouyancy and I do not call that “jumping” any more than I call riding an elevator “jumping”.
In brief: you said and DougC and Fear Itself and Trinopus agreed that a small balloon would help you jump higher. I still say a balloon which provides fractional bouyancy will not help you jump higher unless it has elastic cord tether or it is rigidly attached to your body.
I don’t think that’s very helpful; you didn’t address the question of what buoyancy means. You (I assume) mean by “2 lbs. net buoyancy” that the person has total force which is upwards, and 2 lbs. of downward force is needed to keep him earthbound,
Why not make your starting point around 20 feet in the air – say, the roof. Then you don’t have to worry about the lines going slack. They’ll stay taught even when you hit the ground.
Check this out, sailor:
Be sure to check out the animated gif of the guy jumping into the air.
When your calculations don’t gibe with reality, you need some new calculations; that, and get out of the lab more and get some fresh air.
Jeez, don’t you guys have any opinions on my OP? Seems I hit a nerve with my supposition that slack would affect things. To nit pick just a bit, I did ask if one could tie a bunch of helium filled balloons to oneself, jump such that ones feet were 20 feet off the ground, land, and repeat instantly. I don’t doubt the parabounce system, however it seems to use more equipment than I had suggested.
I don’t question any of the math presented (that’s why I asked), but I wonder how something could help one jump 20 feet in the air, let one glide gently to the ground, and then assist one up to the height of 20 feet again.
I also don’t doubt that balloons would assist ones vertical, and slow one’s descent. To reiterate, is it possible to jump 20 ft in the air, land and repeat several times (given the equipment requirements, homemade stuff)?
Fear Itself, just saw your post as I posted, looks to be that he’s being pulled back to earth with a tether, which is not within the parameters of my OP. The returning to earth part should only be facilitated by gravity. Otherwise it’s not jumping it’s being lifted and then pulled back down.
Let me ask you this: What do you understand by bouyancy?
What do you think the following, taken from their web site, means?
They do not provide any explanation of the meaning of “bouyancy” so we will have to accept it in the common meaning. What do you think is the common meaning of “bouyancy”?
Mexican Jumping Beans. Hollow out the heel of a boot, fill 'er up, and you’re good to go.
Sailor thanks for the input and the enthusiasm you’ve given to my question. Care to hazard a guess regarding my clarification post? I’m guessing you agree with me in that one cannot perform the actions descibed previously without either tethers or a counterweight system. Can’t be done as stated, right?
Sailor, I take your point about 100% buoyancy, but this is not what I have been talking about (although I am assuming 90%+ buoyancy, which was how I read the OP’s statement about not using too much).
Could you just clarify what kind of fraction you have in mind?
All right then. Let’s see if you are willing to put some money where your mouth is. I say that if you jump in the air a balloon tethered to your body with a non-elastic line will not help you jump higher because the string will not be taut until after you have reached the highest point. You are certain I am wrong. I am willing to put some money on this and I am sure you would not want to waste the opportunity to make some easy money with your knowledge. I am willing to lose a few hundred dollars if I am wrong so, here is my challenge: We both put some money in escrow, enough to cover the wager and the costs of the experiment which will also be paid by the loser. The escrow shall only be released to the winner which shall be determined by one or three judges to be chosed and agreed by both sides and who shall be preferably university proffesors in physics, science or engineering. We can agree to accept the verdict of the witnesses or to document it with a high-speed video camera (at least 100fps), the cost of renting it to be born by the loser. We can have an average person do an average jump with some balloons tethered to him or we can design a similar laboratory experiment to keep costs down. It could be a small balloon tethered to a weight which would be propelled 3’ up in the air.
i am willing to wager a few hundred dollars on this (say $500 plus expenses). You can see it all yourself or have others join you. It’s an easy way for you to make money. If you are interested let me know and we can define the details. Feel free to propose whatever conditions or changes you prefer.
Okay, I sense a strong disagreement brewing, people seem to be focusing on matters that (albeit relevant to the OP) are not theorectical answers. The issue is not if the balloons will provide assistance, but whether they can lift one to a height of 20 feet, then allow one to descend to the ground, and repeat this action instantly.
Seems simple enough to me…yes or no?
I still say no, otherwise this would be a popular form of entertainment by now.
I’m not interested in the wager and I don’t feel particularly passionate about this, but I’ll see if I can knock together a small-scale experiment this weekend. It won’t be as rigorous as you’re describing, but If I cannot demonstrate an effect so significant as to be very clearly observable by eye, I’ll concede that there is no effect.