David Thompson
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October 17, 2015

Comments

David

Previously.

Dom

The last guy you see flies away like superman. Supercool!

But how is it possible? Aren't they all falling at the same speed? How do the people at the end of the link join up with the people at the start of the kink?

John D

But how is it possible? Aren't they all falling at the same speed?

"Your terminal velocity is determined by exactly two things–your weight, and the amount of surface area you expose to the ground. While a skydiver can’t do anything about her weight mid-fall, she can control how much area she presents downward. Stomach down, with arms and legs spread out in a kind of belly-flop, the average skydiver is likely to fall at around a hundred and ten miles per hour. By bending arms and legs or angling her body–presenting more or less surface area to the ground–she can change her rate of fall, slowing or speeding up her terminal velocity around ten or twenty miles per hour."

http://indianapublicmedia.org/amomentofscience/skydivers-control-terminal-velocity/

mojo

Not the place for the old superglue handshake trick, obviously.

Col. Milquetoast

They don't seem to be color coordinated in a pattern that I can perceive. Sloppiness at 16 feet per second per second.

Dom

"Your terminal velocity is determined by ... your weight"

That's not right. Didn't Galileo disprove that? Two people are 150 lbs, falling at the same speed. Then they join hands and become a single 300 lb unit. They fall faster?

PiperPaul

Even though "I Fucking Love Science!" I've never quite gotten that feet per second per second thing.

mojo

It's a rate of increase, like all accelerations. The same for all masses, a la Galileo. Outside forces such as air resistance determine terminal velocity, other wise it would keep increasing. Terminal velocity is a dynamic equilibrium.

Britt

Weight has nothing to do with it. It's all about surface area presented against the air below you. Acceleration due to Earth's gravity is 9.8 m/s/s for everything. Only air resistance reduces the downward acceleration. Spread yourself out in the shape of an X and you fall slower, pull you arms and legs in like Superman and you fall faster. Watch a falcon do it: https://www.youtube.com/watch?v=lnT2joxnkqY

R. Sherman

Apollo astronauts prove Galileo to be correct. Without an atmosphere to affect the rate of descent, gravity causes feather and hammer to fall at the same rate.

Sporkatus

Weight absolutely has to do with it. Full summary: the drag that one experiences is based on surface area times several constants and the square of velocity (and a more knotty number, the coefficient of drag - Indiana source is oversimplifying to the point of a lie). This drag is a force, which finds equilibrium with the force of gravity, which is a rate of acceleration (gravitational constant g) *times* mass. The mass of the diver. Galileo is accurate in a vacuum or low speeds only - there is no terminal velocity in a vacuum at all.
In other words, mojo has a simple, correct version of things. Britt does not, nor Dom.

Dom

sporkatus, it sounds like mojo agrees with me and Britt.

WTP

Sporkatus point is valid. Again, rates are constant in a vacuum where there is no force (drag) except for g. Factor in drag and you must account for the mass of the object, or objects depending on perspective. Joining two masses together may not increase their combined drag but it can definitely affect them depending on the configuration. One could be on top of the other thus decreasing drag. Either way, the force of drag must take mass as a factor.

Also remember the case of the astronaut on the moon, even in a vacuum there is the minis clue force of the masses of hammer and feather pulling on the moon. They're just lost in the inverse square root wtf of the gravitational formula.

Not sure if I helped or added to the confusion. I'm in Italy. Last night there was grappa.

Sporkatus

Dom, mojo said that the rate of acceleration is the same for all masses, which in broad terms is correct. However, he did not make the error of expressly leaving mass out of the equilibrium, though he could have been clearer You absolutely did.The force that something exerts is a rate of acceleration times mass ( F=ma), and the drag is an opposing FORCE, not an opposing rate of acceleration. Something which weighs twice as much accelerates at the same initial rate, but takes double the drag (I.e. needs to be going about 1.4 times as fast for the same shape) to reach equilibrium.
Galilean acceleration applies when there is no air resistance. When there IS air resistance, mass is a multiplier on one side of the balance between two forces. Hence why a lead feather falls faster than a real one... in atmosphere. Why is this so bloody hard to understand?

Sporkatus

Apologies for some sharpness there. I was a bit put off by the sense that drag (aerodynamic, not Ru Paul) might be a matter of opinion.

A natural question that arises is, "how is weight one of the two things under control?" Well, all you have to do is make sure that all blokes or blokettes of matching sizes are weighted the same, and then they will fall at the same speed when in the same pose. It's all down to the fattest to set the tone for the rest...

jabrwok

While a skydiver can’t do anything about her weight

I wasn't aware that skydiving was an exclusively female activity. When did that happen?

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