∆V in a human?

[Dman979]

So, this is slightly morbid, but how much ∆V is in a human body?
And what is the best way to get to it?

Let's assume that I've just breathed in. What gives me a better ISP: exhaling through my mouth or nose? Or what if I take the body's assembled molecules and use them as rocket fuel. If I have a proportionally sized engine, what is my ∆V?

And what's the best I can get?

[RainDreamer]

Inb4 someone mentioning beans.

Also, I assume you will get more energy from burning the human body as fuel instead of using it as an engine by blowing air.

[YNM]

The boiling blood, assuming it was done without any form of garment ? Any opening would still means exposure to vacuum though.

But energetically, mushing humans then burn with some LOX is always better. Which is why we propose using methane (or even ethanol) as fuel rocket (already done for ethanol).

[Gaarst]

About the breathing, Isp in seconds is essentially the effective exhaust velocity divided by the surface gravitational acceleration at Earth. So whatever way makes you expell air the fastest gives you the best Isp.


Now the dV:

The average vital capacity (the maximum amount of air you can expel from you lungs) of a grown man is around 4.5 L. That is around 5.7 g or 0.0057 kg of air at standard temperature and pressure.
Suppose you sneeze really hard (but only air is expelled) and expel this air from you lungs in one tenth of a second. You get an air flow rate of 0.045 m[sup]3[/sup]/s.
Suppose the area of your mouth wide open is about 40 cm[sup]2[/sup] or 0.004 m[sup]2[/sup]. The speed of the air is then v = 11.25 m/s.

Plug this in the rocket equation: dV = v * ln(m[sub]0[/sub]/m[sub]1[/sub]).
Your average man is 70kg, so:
dV = 11.25 * ln(70 / (70 - 0.0057)) = 0.9 mm/s

So about 1 mm/s of dV you can get by breathing really hard, this is not much...


For the whole body, I guess it depends on the way you use the molecules contained inside it. Lots of chemistry and biology involved there, and I'm only a physicist :P

[Streetwind]

You might be interested in [URL="https://www.reddit.com/r/askscience/comments/3569v1/if_you_farted_hard_enough_in_space_could_you_move/"]this Reddit thread[/URL]... in the same way that juvenile humor is interesting... :P

[AeroGav]

On a more serious note, animal fat has a chemical composition not that far apart from hydrocarbons and in terms of energy per kg is only a couple percent behind.

Our muscles generally transform about 20% of the chemical energy into kinetic/potential energy and the rest comes out as waste heat. Similar to a high bypass turbofan operating near its design point in fact.

Furthermore, a goose has similar lift:drag ratio to an airliner wing, and at the start of it's migration, it's fuel fraction (fat percentage) is similar to what a long haul airliner takes off with.

So no surprises that long haul airliners and migratory birds fly similar unrefuelled distances.

It's a bit harder to apply all this to a human, but let's imagine you have a bicycle with a streamline body fairing that's so good the coefficient of drag goes to zero, and unobtainium tyres with zero rolling resistance. A typical westerner climbs into the saddle with 30% body fat, and keeps pedalling until they burn down to 10%. In this scenario the human body does have a delta-V. The question is, would you be able to realise it, or would you be forced to stop pedalling due to the wheels no longer making contact with ground, having achieved orbital velocity?

[Kerbart]

[quote name='RainDreamer']Inb4 someone mentioning beans.

Also, I assume you will get more energy from burning the human body as fuel instead of using it as an engine by blowing air.[/QUOTE]

Why stop there? If we use Doc Brown's mass converter we can turn it straight into energy and get *a lot* more out of it.

[kerbiloid]

Kethane mod contains a ready-to-use KE-WAITNONOSTOP-01 Kerbal Unreconstitutionator converter which you can use to convert Kerbal into Kethane in situ.
So, you can get a practical answer for Kerbals.

[Shpaget]

[quote name='kerbiloid']Kethane mod contains a ready-to-use KE-WAITNONOSTOP-01 Kerbal Unreconstitutionator converter which you can use to convert Kerbal into Kethane in situ.[/QUOTE]
That is simultaneously the most disturbing device ever made, and a very noble one.

As for the original question, it's hard to answer. If you're limited to use nothing but a human, then [I]very[/I] little. There is very little unreacted oxygen available for combustion, so without adding additional oxidizer, you won't be able to extract much of the energy.
If you can use additional oxidizer and some king of an engine, then the numbers go up, but with that logic you can use the body just as reaction mass (with necessary energy and hardware provided), at which point dV is theoretically unlimited.

[AeroGav]

Is it possible to calculate your delta V when using a step climber machine at the gym?

Futhermore, it should be possible to derive the specific impulse of a fuel, like an energy gel or sports drink from the calories used vs distance/mass climbed.

I suspect that carbohydrate based sports drinks are going to perform like alcohol/peroxide mixtures or some other lower energy liquid fuel.

[wumpus]

Less morbid answer.
KE=1/2(mv**2)
PE=mgv
so KE at launch (the delta-V) is entirely converted to PE at apogee
1/2(mv[SUP]2[/SUP])=mgh
v[SUP]2[/SUP]=2gh
delta-v=square_root(2gh)
so for a 1m vertical leap (serious jumpers like Micheal Jordan or Karch Kiraly in their primes. And for all I know they might still pull close to that off).
delta-v=root(2*9.8)=~4.4m/s

[problemecium]

Simple: oodles.

1. Place human inside giant ring-shaped nuclear-powered electromagnet.
2. Use a magnetic pulse to compress the human to the size of a virus, causing it to form a black hole.
3. Harvest Hawking radiation from said black hole to produce enough energy to level New York City or accelerate a small spacecraft clear out of the Solar system.

[More Boosters]

[quote name='parameciumkid']Simple: oodles.

1. Place human inside giant ring-shaped nuclear-powered electromagnet.
2. Use a magnetic pulse to compress the human to the size of a virus, causing it to form a black hole.
3. Harvest Hawking radiation from said black hole to produce enough energy to level New York City or accelerate a small spacecraft clear out of the Solar system.[/QUOTE]

That blackhole will evaporate instantly. It would also have, for a 100 kg human, an event horizon radius of 1.485 x 10^-25,

[wumpus]

DeltaV is a measurement of an entire rocket (boosters and payload). You can't claim the human is just the fuel and work out deltaV from that. You can say that a [highly skilled athlete] can get to 4 m/s by jumping. Or you can build a "rocket" that would be the equivalent of a command chair and ion thruster. You could then work out how much deltaV the human could produce if all the electricity for the ion thruster can from a "command chair" with "spinning class" cycle wheel used to generate electricity. The big catch is that you still need to define when the human stops. Max output in a single day? Max output without additional feeding (cut the xenon, you won't need much)? DeltaV just doesn't work well for this type of thing. With enough food, water, and air the limits become the life support and xenon supplies, not the human (well there is the lifespan).

Stop watching the Matrix. That was dumb and you should forget it.

[problemecium]

[quote name='More Boosters']That blackhole will evaporate instantly. It would also have, for a 100 kg human, an event horizon radius of 1.485 x 10^-25,[/QUOTE]

Why yes, yes it would. So prepare for some serious G-force ;P

[More Boosters]

[quote name='parameciumkid']Why yes, yes it would. So prepare for some serious G-force ;P[/QUOTE]

More like a rather powerful explosion. How do you harness energy from millions of nuclear bombs detonating at the same time?

[PB666]

The changeover screwed up the title, its should be Delta as in dV