Skydiving Physics.

[strop45 0]

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It was just so frustrating to hear them all agree about something that i KNOW is not true, but can't explain.

Part of the problem might be that you are confusing size(drag) and mass(weight).

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The entire class and teacher all agreed together that a smaller person when compared to a bigger person would fall faster

Looking back at your original post, a smaller skydiver does go faster than a larger one of the same mass (weight), so perhaps your classmates were thinking of skydivers of the same mass. Compare the short fat skydiver to a tall thin one of the same weight - which is faster?

The difference between stupidity and genius is that genius has its limits." -- Albert Einstein

[format 1]

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short fat skydiver to a tall thin one of the same weight

= short one. OP gets it (I beleive)

Now for you: tear the peace of B5 paper, drop them both simultaneously from 10 ft (flat drop).

A hint: there are no cubes here

What goes around, comes later.

[MakeItHappen 15]

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Compare the short fat skydiver to a tall thin one of the same weight - which is faster?

ok

Equal drag coefficients means equal body positions.

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DiveMaker

[Kami-kaze 0]

OP
Do you understand calculus ?
It's a differential equation.

The only drag that matters is the surface area x-z plane. (horizontal) your head, shoulders , arm, legs that hits the air. What's vertical and in the streamline, you can neglect, unless you have lots and lots of material flapping along you. You are slicing fluid, let's leave it like that.
So, yeah, body position. Head down and belly guess what the result is gonna be ?

[MakeItHappen 15]

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OP
Do you understand calculus ?
It's a differential equation.

I took calculus in high school.
I took so many math classes in college that I had a double major in math.
HS grad 74
BS grad physics Illinois State Univ. 76 with high honors
MS grad physics Purdue Univ 78 with high honors

Do you need an explanation on how to read graphs?

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DiveMaker

[jcd11235 0]

I'm fairly sure Kami-kaze's post was directed at the OP, despite clicking the reply button on your post.

Math tutoring available. Only $6! per hour! First lesson: Factorials!

[MakeItHappen 15]

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I'm fairly sure Kami-kaze's post was directed at the OP, despite clicking the reply button on your post.

Whatever.
The fact is that the explanation does NOT involve calculus or differential equations.
Simple algebra and reading graphs is all it takes.

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DiveMaker

[Kami-kaze 0]

Of course it does.
It involves drag and air density.

O.K I might be making it complicated myself. Let me think some more ...

[MakeItHappen 15]

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OP
Do you understand calculus ?
It's a differential equation.

The only drag that matters is the surface area x-z plane. (horizontal) your head, shoulders , arm, legs that hits the air. What's vertical and in the streamline, you can neglect, unless you have lots and lots of material flapping along you. You are slicing fluid, let's leave it like that.
So, yeah, body position. Head down and belly guess what the result is gonna be ?

ok

assume equal weights and vary the body position

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DiveMaker

[format 1]

I thought different body area
I am sorry (poor excuse: poor getting English)

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tear the peace of B5 paper, drop them both simultaneously from 10 ft (flat drop).

It might be revealing to more than me (your answer I mean)

What goes around, comes later.

[Kami-kaze 0]

I still think it is a D.E MakeItHappen.
Cos when you jump from a plane you have horizontal velocity, so you have a parabolic trajectory.

[MakeItHappen 15]

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I still think it is a D.E MakeItHappen.
Cos when you jump from a plane you have horizontal velocity, so you have a parabolic trajectory.

The original post was talking about terminal velocities. Introductory physics classes do not get into studying jerks, aka the time rate of change of acceleration.

In a nutshell you have 3 items to adjust fallrate:
1 - weight
2 - projected area
3 - drag coefficient

Body position influences projected area and drag coefficient.

From a practical standpoint, these are weight, trim (aka body position) and jumpsuit.

See also What determines Fall Rate?

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[dks13827 3]

invite all of em out to the DZ !! and those that want to.. can do a jump.. or even observer rides !!

[mjosparky 4]

I am going back and lay down again.

Sparky

My idea of a fair fight is clubbing baby seals

[Kami-kaze 0]

O.K
so when it's head down :
You have similar shape (profile) and assuming you are streamlined shape with arms and legs tucked in, Not much surface area (frontal area) difference in air resistance, assume similar material and the skin drag is negligible, less air density higher up means less drag coefficient and increases as you fall, you only got mass difference.

Belly, you have lots of air resistance from surface, skin drag close to 0% , coeff has more effect, and we have mass difference.

[Kami-kaze 0]

It's 3 in the morning here, so my brain is a bit ...
sorry about the confusion

[lost_n_confuzd 0]

KISS - Keep it simple, stupid.

Weight = Penetrating Force: the more force, the faster you will fall. Surface area "counters" the weight, or penetrating force.

A bowling ball will fall faster than a baseball. The weight of the bowling ball is greater than it's surface when compared to a baseball that, in lamens terms, could be considered weight/surface area proportional as opposed to the bowling ball that is heavy as hell.

[JohnMitchell 16]

Okay, you're in the military. Explain it in terms of sectional density, same as used in firearms ballistics. The bigger skydiver, if you look at the cross section, is thicker than the smaller skydiver, resulting in a higher ballistic coefficient, meaning higher terminal velocity.

I'm kind of shocked that a physics professor couldn't have thought his way through this one a little better. I've heard everything from whuffos, but I expect more from a PhD.

[kallend 2,032]

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Of course it does.
It involves drag and air density.

O.K I might be making it complicated myself. Let me think some more ...

There should be a law to prevent people from practicing physics without a license.

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The only sure way to survive a canopy collision is not to have one.

[kallend 2,032]

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I still think it is a D.E MakeItHappen.
Cos when you jump from a plane you have horizontal velocity, so you have a parabolic trajectory.

No, you don't. AIR RESISTANCE causes significant deviation from a parabola.

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The only sure way to survive a canopy collision is not to have one.

[Kami-kaze 0]

Sure, I understand that. But we are not talking about shooting a cannon ball from the ground and calling it a parabola.
Anyway, it's skewed and that's what I wanted to say, air resistance.
No, i didn't need anything other than a university bridging course to study physics. But I didn't get my licence to practice, either. Thank goodess for that, it was taking up too much of my time and physics professors are social misfits. I thought I'd fit in.

[timmyfitz 0]

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Sure, I understand that. But we are not talking about shooting a cannon ball from the ground and calling it a parabola.
Anyway, it's skewed and that's what I wanted to say, air resistance.
No, i didn't need anything other than a university bridging course to study physics. But I didn't get my licence to practice, either. Thank goodess for that, it was taking up too much of my time and physics professors are social misfits. I thought I'd fit in.

And don't forget about the arrogance and the undeserved feeling of self importance.

[LloydDobbler 2]

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I am going back and lay down again.

Sparky

+1

Signatures are the new black.

[JackC 0]

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There should be a law to prevent people from practicing physics without a license.

+1