terminal & sub-terminal??

[Squeak 17]

Ok guys,
What is terminal and sub-terminal, I take it to mean terminal velocity.
If this the case, I am suposed to do a sub-terminal opening on a forthcoming jump.
How do you know when you reach terminal velocity?
Will it be the same for all falling bodies, regardless of size shape andor weight??

You are not now, nor will you ever be, good enough to not die in this sport (Sparky)
My Life ROCKS!
How's yours doing?

[ernokaikkonen 0]

>What is terminal and sub-terminal, I take it to mean terminal velocity.

That's right. 'Terminal' refers to terminal velocity, 'sub-terminal' refers to speeds less than terminal velocity(which means that you keep accelerating)

>If this the case, I am suposed to do a sub-terminal opening on a
>forthcoming jump.

Why? Is this a part of some training progression?

>How do you know when you reach terminal velocity?

Well, when you don't accelerate anymore... On belly-to-earth jumps, one usually reaches terminal velocity at about 12 seconds.

>Will it be the same for all falling bodies, regardless of size
>shape andor weight??

Of course not. When you're freeflying, your TV is higher than when you're flying belly-to-earth, since you're weight is the same(the gravity pulls you towards the earth at the same rate), but your surface-area presented to the relative wind is smaller(so there's less drag to fight the gravity).

Erno

[quatorze 1]

>If this the case, I am suposed to do a sub->terminal opening on a forthcoming jump.

>Why? Is this a part of some training progression?

more than likely and at least one hop and pop is required to be eligble for the USPA A- liscence.


By the way, subterminal openings are kind of cool, you get to feel your stow bands release.

I'm not afriad of dying, I'm afraid of never really living- Erin Engle

[Jimbo 0]

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Will it be the same for all falling bodies, regardless of size shape andor weight??

In a vacuum, but you wouldn't like that, you'd probably explode.

-
Jim

"Like" - The modern day comma
Good bye, my friends. You are missed.

[ernokaikkonen 0]

>In a vacuum, but you wouldn't like that, you'd probably explode

Actually, in a vacuum there would be no terminal velocity... He'd accelerate until impact. And weight would still play a part in his rate of acceleration.

(edit:) Umm.. No? Yes? Now I'm second-guessing myself... Earths gravitational pull causes acceleration of ~10m/s^2. But heavier objects must fall faster. SO where does weight come in the equation? damnit.

BillVon? Help, please?

[wmw999 2,116]

It's weight combined with surface area and shape. Weight only counts where there's air, I'm pretty sure. At least that's what I remember Dr. Flarys telling me in hs.
Wendy W.

There is nothing more dangerous than breaking a basic safety rule and getting away with it. It removes fear of the consequences and builds false confidence. (tbrown)

[Samurai136 0]

weight and mass are different.

Mass is measured in Kg.

Ignoring air resistance two objects fall at the same rate because their acceleration is the same. accel due to gravity. Even though one object may be twice as massive it has more inertia to overcome; hence they fall at the same rate.

F=ma a=10m/s^2

for differing masses the force on one may be greater but it's inertia (resistance to change) is also greater.

Hope thatt helps.

Ken

"Buttons aren't toys." - Trillian
Ken

[stalker 0]

Quote

But heavier objects must fall faster.

That rumbling sound? Galileo turning in his grave.

[Cajones 0]

This' getting waaay to theoretical, but... Comparing two objects of differing mass. If you were falling toward the Earth in a vacuum, the object with the greater mass would accelerate more. This is due to the pull generated on the Earth by the objects.
It goes back to the old saying "Fat women are more attractive, because they have more mass." Every object has its own gravitational field. Just as the Earth has a gravitational field that pulls us all towards it (keeping us from flying off into space), we all generate a gravitational pull that pulls the Earth towards us (as well as other objects). It is altogether minute in comparison to the pull generated by heavenly bodies (and we all know how attractive heavenly bodies are), but it could be a factor in this model.

The laws of physics are strictly enforced.

[ernokaikkonen 0]

>>But heavier objects must fall faster.
>>
>
>That rumbling sound? Galileo turning in his grave.

So why do I bother wearing a weight vest?

[Cajones 0]

'Cuase you'd die jumping with the gear you have - in a vacuum.

The laws of physics are strictly enforced.

[billvon 2,380]

>Earths gravitational pull causes acceleration of ~10m/s^2. But
> heavier objects must fall faster. SO where does weight come in the
> equation? damnit.

Heavier objects do not fall faster. Drop a cannonball and a feather on the moon and they will both hit the ground at the same time.

>This' getting waaay to theoretical, but... Comparing two objects of
>differing mass. If you were falling toward the Earth in a vacuum, the
> object with the greater mass would accelerate more. This is due to
> the pull generated on the Earth by the objects.

Again, not true. For a concrete example, look at the Apollo 13 mission. They were falling towards the Earth when they undocked the LM from the much-heavier CM/SM. Even though one was ten times the weight of the other, they stayed relative to each other, and they needed a nudge (from the RCS) to separate them.

[Cajones 0]

>This' getting waaay to theoretical, but... Comparing two objects of
>differing mass. If you were falling toward the Earth in a vacuum, the
> object with the greater mass would accelerate more. This is due to
> the pull generated on the Earth by the objects.
Again, not true. For a concrete example, look at the Apollo 13 mission. They were falling towards the Earth when they undocked the LM from the much-heavier CM/SM. Even though one was ten times the weight of the other, they stayed relative to each other, and they needed a nudge (from the RCS) to separate them.

Actually - it is true. The actual force is so small, in this example, it is immeasurable. If you launch another planet, and an aircraft carrier at the Earth through space, now we're talking something noticeable. The planets will pull on each other (and the planet and aircraft carrier will, too), and the planet will, given enough time, accelerate faster than the carrier.

The laws of physics are strictly enforced.

[ernokaikkonen 0]

Ok, I think I got it now:

without atmosphere:
-Drop a cannonball or football on a planet; they hit the ground at the same time for any practical reasons.
-Drop a moon on a planet, it wouldn't hit the ground any sooner than the football, except that the planet would be falling at the moon too, so they impact sooner.

And with atmosphere:
- Me with my weight-vest falls faster than me without it, because... ... Nope, it's getting late on this side of the globe, I'm not getting it...

[billvon 2,380]

>Actually - it is true. The actual force is so small, in this example, it is
> immeasurable. If you launch another planet, and an aircraft carrier
> at the Earth through space, now we're talking something noticeable.
> The planets will pull on each other (and the planet and aircraft
> carrier will, too), and the planet will, given enough time, accelerate
> faster than the carrier.

Again, no. They will accelerate towards the earth at the same speed. Now, if you measure the time it takes them to impact the earth, the other planet will take less time, since the earth is being attracted towards the other planet (assuming they both started at the same spot.) But at the instant you release them, they will both accelerate at exactly the same speed. And if you keep the earth stationary, their speeds will match all the way to the atmosphere.

[Scoby 0]

Quote

And with atmosphere:
- Me with my weight-vest falls faster than me without it, because... ... Nope, it's getting late on this side of the globe, I'm not getting it...

It is because the amount of downward force increases when you add weight, while the amount of drag countering the weight stays the same. You keep accelerating until the forces reach equilibrium, which is at a higher speed than before. This equilibrium is known as terminal velocity.

[Cajones 0]

I'm with you, now. Now... How much wood would a woodchuck chuck if a woodchuck could chuck wood?

The laws of physics are strictly enforced.

[Cajones 0]

Isn't he really just increasing his density? I've noticed some of the really dense people at my DZ fall really fast...

The laws of physics are strictly enforced.

[kallend 1,621]

Assuming you make your jump from a plane and not a balloon, and belly fly...

You initially inherit the plane's forward speed, typically 90kt or so indicated, as your forward velocity. You also start with zero vertical velocity. Drag rapidly bleeds off your horizontal velocity while gravity causes you to accelerate vertically. The net result is that initially your total (vector sum) airspeed decreases, to about 80kt, taking around 4 seconds, before the vertical component of velocity becomes dominant.

After around six seconds your horizontal velocity has decayed to almost nothing, and you are now falling vertically and still picking up vertical speed. 8 seconds or so into the skydive you have reached about 90% of your terminal velocity. You reach essentially constant speed (at which the forces of gravity and air resistance balance out) about 10 - 12 seconds into the jump, if belly flying.

www.iit.edu/~kallend/skydive/ for a freefall simulation.

SO for deployment at lowest airspeed, throw out about 4 seconds into the jump.

jk (PhD in physics)

[Squeak 17]

SooooBack to the reason I posted this in the 1st place, how do I tell if I'm still sub-terminal when I pull my ripcord???

You are not now, nor will you ever be, good enough to not die in this sport (Sparky)
My Life ROCKS!
How's yours doing?

[SkydiveMonkey 0]

A good test - from the top of a cliff / building / whatever, get a large rock and a small rock, and drop them off the side at the same time. You will see initially that they fall away at the same rate

____________________
Say no to subliminal messages

[indyz 1]

Quote

Back to the reason I posted this in the 1st place, how do I tell if I'm still sub-terminal when I pull my ripcord???

Pull before 10 seconds or so are up. Ask your instructors, they might want at least an x second delay, but not more than y seconds.

[quatorze 1]

Quote

>Actually - it is true. The actual force is so small, in this example, it is
> immeasurable. If you launch another planet, and an aircraft carrier
> at the Earth through space, now we're talking something noticeable.
> The planets will pull on each other (and the planet and aircraft
> carrier will, too), and the planet will, given enough time, accelerate
> faster than the carrier.

Again, no. They will accelerate towards the earth at the same speed. Now, if you measure the time it takes them to impact the earth, the other planet will take less time, since the earth is being attracted towards the other planet (assuming they both started at the same spot.) But at the instant you release them, they will both accelerate at exactly the same speed. And if you keep the earth stationary, their speeds will match all the way to the atmosphere.

you think that maybe this is a touch more than the original question was asking for?

I'm not afriad of dying, I'm afraid of never really living- Erin Engle

[jumpy 0]

hmm i don't get much of the above although i just got back from work.....but i was always told by my (granted rather doppy) science teacher that a brick and a feather droped from the same height would eventually fall at the same speed? This never made sence to me though with wind resistance and all that.....hmmmmm

[drenaline 0]

if am not mistaking, if you have wind resistance some objects will fall at different speeds at terminal, but with no wind resistance all object will fall at the same speed at terminal cause there is no drag and the acceleration is the same. The weight of the object counteracts for the drag caused by the fluid in this case its the wind (yes wind is a fluid in the lab).

In particle dynamics the weight is considered a force as well as the drag caused by the fluid (its called friction force), in our case the weight + gravity push us down and the drag of the mass exposed to the wind (friction force) tries to push us up (kinda complicated) until the system reaches a balance and it wont get more speed and thats what we call terminal. If you don't understand I will try to put it in a clearer way, just ask. Hope I could of been of some help.

HISPA 21
www.panamafreefall.com