Why no Artificial Gravity ??

[Hellbound]

Hmmm.

When running, you would actually have a less than constant speed.

You're only actually accelerating during the phase in which your foot is in contact with the ground. In between the contact phases, you're actually slowing down as air resistence slows you. Even in vacuum, the "in-between" stages are free of acceleration, although you might not lose speed.

Now, as someone point out, running is not free of "up-down" motion. So, when trying to run in lower gravity, each "bound" is going to be longer, as your push-off will take you higher and further. This, in turn, limits the amount of foot-ground contact time overall, thus limiting the amount of time you have to actively accelerate in a horizontal direction. This is why, for the astronauts, it was faster to "hop" on the moon than try to walk or run. But even this hop was slower than a full-out sprint under 1G.

You'd be slower in low gravity.

Least that's my argument.

 

[Just thinking]

Evidence? What is your evidence that you can move faster in say .5g and even faster in .1g? Yes a given speed might not take the same output of energy, and for some people that might be a limiting factor in speed in 1g so they would go faster, but say for a good sprinter, in say .1g how much faster can they go?

Well, let's start with the car analogy -- which I think is not a very good one to apply to humans. A car has two completely separate systems at work that are involved during forward motion -- the suspension system and the drive system. The suspension is what supports the vehicle's weight, less the unsprung weight (wheels, tires, etc.). The drive system is what propels the car forward, and does not have to bleed off any part of that energy to support the car. All of the drive system's energy can go into forward motion; and even if the car were put into a lower gravity field, things wouldn't change as far as the suspension and drive systems go. Humans, however, only have legs -- and they must do double duty. Not only must they support your weight but they must also supply the forces needed for forward motion. Therefore, the amount of energy that can go into forward motion will be a fraction of your legs' total energy output.

When running, you are not standing on both legs at the same time, hence you must continuously apply the energy needed to offset the full acceleration of Earth's gravity to prevent falling on your face. This is done by launching yourself off of one foot onto the other. Even if you give this as 50% of your weight, it is significant -- consider the energy needed to continuously accelerate 50% of your weight at 10 metres per second per second. And we haven't even factored in the energy you use to keep running -- although momentum will greatly help you there. But if gravity is reduced to say only 1/3 of Earth's, think of how much less energy your legs must dedicate to merely holding you up. That energy can now go into forward motion where it didn't before. Why? Because as I said earlier, your legs are dual function -- it's all going to come down to how you divide up their use.

 

[Just thinking]

... You'd be slower in low gravity.

Least that's my argument.

Do you think you would run faster then, in say, 1.5G ?

 

[Just thinking]

Now, as someone point out, running is not free of "up-down" motion. So, when trying to run in lower gravity, each "bound" is going to be longer, as your push-off will take you higher and further.

You seem to be assuming that one would not alter their running style when in a lower G field -- I doubt that would be the case, as one adjusts when running downhill as opposed to level ground. As for the "up-down" motion you'll see I addressed that in post 82.

 

[rdaneel]

Wouldn't it depend on the size of the toroid? I always thought the larger it is, the slower it has to spin to maintain 1G, or is my memory of high school science completely shot?

Do we have a math wiz around who can calculate what diameter a torus has to be to have a pull of 1G and be slower than a human can run?

 

[Just thinking]

Wouldn't it depend on the size of the toroid? I always thought the larger it is, the slower it has to spin to maintain 1G, or is my memory of high school science completely shot?

Do we have a math wiz around who can calculate what diameter a torus has to be to have a pull of 1G and be slower than a human can run?

The equation for centripetal acceleration (G) is ...

a = (v v) / R

... where v is linear velocity in m/s
R is the radius of rotation in metres
a is acceleration in m/s/s

If we let a = 10 m/s/s
and v = 10 m/s (approx. 20 mph)

... then R is approx. 10 metres.

If we reduce the running speed to a mere 10 mph, the radius shrinks to just 2.5 metres ... pretty small ring.

So as the ring gets larger its angular velocity becomes less (rpm's), but the linear velocity (the speed of a point going around the circumference) increases.

 

[rdaneel]

Thank you.
So basically any ring with a slow enough linear velocity that it could be "outrun" would be to small to be very practical.

 

[Just thinking]

Thank you.
So basically any ring with a slow enough linear velocity that it could be "outrun" would be to small to be very practical.

Quite true. But remember, you requested an acceleration of 1 full G. The velocities diminish quite a bit for something like 1/3 gravity. Plus -- and this is the interesting part -- once you start running counter to the ring's motion, the centripetal effects of its artificial gravity become reduced. And if what I believe to be true is actually the case (you can run faster in lower gravity) it will become easier to run faster the faster you go. To a point, of course.

PS ... you're quite welcome.

 

[rdaneel]

I wonder what happened to the artificial gravity research that was in the news a few years ago. Is it still being worked on or did it go the way of "cold fusion"?

 

[Hellbound]

Do you think you would run faster then, in say, 1.5G ?

No, and I didn't even imply it. I've not considered the high gravity case, only low gravity.

You seem to be assuming that one would not alter their running style when in a lower G field -- I doubt that would be the case, as one adjusts when running downhill as opposed to level ground. As for the "up-down" motion you'll see I addressed that in post 82.

The running style was the reason I brought up moon walking. The astronauts adjusted their gait, and the best was not anything like a walk or run, but the type of hopping motion they ended up on. I'm saying that a running gait, however modified, won't be useful below a certain minimal threshold.

The effect of the up-down motion I brought up has nothing to do with anything you posted in post 82. Not to mention your reasoning in post 82 is flawed, because many of the muscles used to push forward are different from those used to hold you up, and mopst of those that are used in both are used differently for forward motion than standing upright. In any case, the amount of force required to move you in a direction parallel to the force of gravity won't change, and the small amount of muscle energy used to stand against gravity (with is mostly a matter of tiny adjustments to balance on bones, which hold most of the weight) is going to add any appreciable increase in speed.

Could you move faster in zero-G or low-G? Possibly, depending on the type of movement...and likely you could move for a longer time. However, I feel confident that such motion would not be running in any fashion recognizable to what happens in normal gravity.

 

[Ysidro]

Hahah I could picture the astronauts landing on mars and not being able to walk straight because of compensating for the coriolis force. They would all be drifting to the left....

Hah! We had a dog who eventually learned to go down a small spiral staircase in a house we moved to back when I was a lad. Eventually he couldn't go up or down straight stairs without moving on an angle.

 

[Just thinking]

No, and I didn't even imply it. I've not considered the high gravity case, only low gravity.

The running style was the reason I brought up moon walking. The astronauts adjusted their gait, and the best was not anything like a walk or run, but the type of hopping motion they ended up on. I'm saying that a running gait, however modified, won't be useful below a certain minimal threshold.

I've mentioned that too, by specifically saying "Low gravity" and emphasizing not Zero gravity. As to just how low gravity would have to be before one's gait would have to be severely altered may just have to wait for actual empirical data. But that aside, whether hopping, walking or running (or whatever) there is absolutely no evidence that one can get around on Earth in a full moon suit as quickly as they did on the Moon.

The effect of the up-down motion I brought up has nothing to do with anything you posted in post 82. Not to mention your reasoning in post 82 is flawed, because many of the muscles used to push forward are different from those used to hold you up, and most of those that are used in both are used differently for forward motion than standing upright. In any case, the amount of force required to move you in a direction parallel to the force of gravity won't change, and the small amount of muscle energy used to stand against gravity (with is mostly a matter of tiny adjustments to balance on bones, which hold most of the weight) is going to add any appreciable increase in speed.

I believe the weight of one's body is suspended quite differently when standing as opposed to full running -- specifically as far as bones go. When running fast, like a sprinter, the leg is not fully extended directly beneath the person, hence they (bones) cannot be supporting as much of one's weight as when standing. The body is suspended by a pushing up from one step to the next -- the net result being a force opposite to that of gravity. And this comes from the muscles. I don't think it's that small in terms of energy output.

Could you move faster in zero-G or low-G? Possibly, depending on the type of movement...and likely you could move for a longer time. However, I feel confident that such motion would not be running in any fashion recognizable to what happens in normal gravity.

On that I guess we'll just have to wait and see.