Why would I die when I jump out of a plane?

[theboeh]

So if F=ma and the Earth's gravity provides a constant acceleration then why would I die if I jump out of an airplane but not if i jump off a 10 foot ledge? I'm sorry if this is a stupid question but it's been several years since I was in a physics classroom.

 

[Pengwuino]

Yes, its a constant acceleration which means your speed is increasing at a constant rate. A roughly 10m/s acceleration means that in 2 seconds, your traveling at 20m/s and at 10 seconds, your at 100m/second and if you live to 100 seconds, your traveling at 1km/second (well theoretically, friction slows you down).

 

[SpaceTiger]

It's also worth remembering that the force on your body has to do with how quickly you decelerate when you hit the ground, which is related to the velocity you're hitting it with. The reason that you're better off landing on a giant foam rubber pad than a pile of rocks is that the foam rubber pad will decelerate you more slowly (relatively speaking), inducing less of a force on your body.

 

[scilover89]

The equation is:
Ft=m(v-u)
So, if you have higher velotion, you will receive greater force when you hit the floor

 

[whozum]

The force you hit the ground with isn't what kills you, its the impulse, or time derivative of force. At 10m/s (25mph) you would survive a crash whereas at 100m/s (250mph) you are going to impart a lot more energy in the same time interval (much higher impulse) which is what kills you.

Keeping air resistance in mind, terminal velocity is about 100-150 mph, so once you hit that speed your not going to accelerate any longer and will be in freefall. Given a height of jump "h1" where terminal velocity is reached during the fall, any height greater than h1 will result in the same speed of downfall and therefore the same impact velocity.

 

[SpaceTiger]

The force you hit the ground with isn't what kills you, its the impulse, or time derivative of force.

Impulse is

Fdt

not the time derivative of force. It represents the instantaneous momentum transfer, not energy.

Keeping air resistance in mind, terminal velocity is about 100-150 mph, so once you hit that speed your not going to accelerate any longer and will be in freefall.

Free fall is not when you hit terminal velocity. You're in free fall from the moment you jump.

 

[Andrew Mason]

The force you hit the ground with isn't what kills you, its the impulse, or time derivative of force. At 10m/s (25mph) you would survive a crash whereas at 100m/s (250mph) you are going to impart a lot more energy in the same time interval (much higher impulse) which is what kills you.

This is not correct. It is the force that kills you. If you landed on a huge air pillow (as stunt people do when they dive off buildings) you would not be hurt at all but you still experience the same change in momentum. If you increase the time over which the change in momentum occurs you reduce the force.

AM

 

[pervect]

So if F=ma and the Earth's gravity provides a constant acceleration then why would I die if I jump out of an airplane but not if i jump off a 10 foot ledge? I'm sorry if this is a stupid question but it's been several years since I was in a physics classroom.

The short answer is that you don't die when you jump out of an airplane, you only die when you hit the ground :-)

What's important is the velocity you have when you hit the ground. The velocity you have when you hit the ground depends both on the acceleration of Earth's gravity and the distance you fall - v = sqrt(2*a*d) in the absence of air resistance, to be exact.

 

[Chronos]

I'm hesitant to leap off a 10 foot ledge and splat on concrete. I think it would hurt. But I don't doubt it would be fun to watch.

 

[tony873004]

There are some people who have jumped out of an airplane and lived. I was watching something on TV a few years ago about survivors of parachute accidents.

The short answer is that you don't die when you jump out of an airplane, you only die when you hit the ground :-)

That reminds me of...
"Guns don't kill people... bullets do"
as a humorous rebuttal to the "Guns don't kill people, people kill people" bumper sticker.

 

[Danger]

There are some people who have jumped out of an airplane and lived. I was watching something on TV a few years ago about survivors of parachute accidents.

If the chute deployed without properly opening, it would act as an aerobrake to a far lesser extent than normally, but it would still decrease terminal velocity. Therefore, less splat. Also, the last case that I heard of landed on really soft ground.

 

[russ_watters]

This is not correct. It is the force that kills you. If you landed on a huge air pillow (as stunt people do when they dive off buildings) you would not be hurt at all but you still experience the same change in momentum. If you increase the time over which the change in momentum occurs you reduce the force.

AM

What you just described is impulse (though I think it would be the time integral of force - force times time).

 

[Andrew Mason]

What you just described is impulse (though I think it would be the time integral of force - force times time).

Yes. Impulse = \int Fdt = \Delta p

AM

 

[Uno Lee]

I fell down a cliff one time, I figure that it was about 10 m. In mid free fall, head first, I had the thought that I had better do something, so I somehow spun my body end for end , it must have looked like a back flip, and landed in a sitting position in a clump of vine maples with no impact. Does a spinning body land with less impact and if so why?

 

[whozum]

This is not correct. It is the force that kills you. If you landed on a huge air pillow (as stunt people do when they dive off buildings) you would not be hurt at all but you still experience the same change in momentum. If you increase the time over which the change in momentum occurs you reduce the force.

AM

This is exactly what I meant to say, I got the terms mixed up.

 

[whozum]

Impulse is

Fdt

not the time derivative of force. It represents the instantaneous momentum transfer, not energy.


Free fall is not when you hit terminal velocity. You're in free fall from the moment you jump.

I meant free fall in the sense of weightlessness, at terminal velocity his net force will be 0. Kind of like the astronauts in space.

 

[whozum]

I fell down a cliff one time, I figure that it was about 10 m. In mid free fall, head first, I had the thought that I had better do something, so I somehow spun my body end for end , it must have looked like a back flip, and landed in a sitting position in a clump of vine maples with no impact. Does a spinning body land with less impact and if so why?

No, you may deflect the energy better by molding your body in a more comfortable falling position, but the same amount of energy is dissipated. It depends on how you spin.

But a spinning ball for example, spin will not affect the impact force much if at all.

 

[Andrew Mason]

I fell down a cliff one time, I figure that it was about 10 m. In mid free fall, head first, I had the thought that I had better do something, so I somehow spun my body end for end , it must have looked like a back flip, and landed in a sitting position in a clump of vine maples with no impact. Does a spinning body land with less impact and if so why?

No. There may be a slightly slower impact speed for the part that is spinning 'up' when you hit but there is another part of you that will have a slightly higher impact speed (ie. the part opposite that is going 'down' when you hit). You can't slow down your centre of mass by spinning.

Now, in your fall, there could not have been 'no impact'. Fortunately you were not hurt. It seems that the branches that you landed on applied a gentle stopping force by bending and spreading that force out over some time and distance.

AM

 

[Creator]

The short answer is that you don't die when you jump out of an airplane, you only die when you hit the ground :-)

Yea, it's not the fall that gets you; its the sudden stop. he,he.

--------------------------------------------------------------------------
--If at first you don't succeed, don't try skydiving! --

 

[Uno Lee]

Well, I did land with about as much impact as sitting down on a couch and I did have a minor scrape on my knee from the cliff but I was amazed looking up at the height I had just fallen that nothing serious had happened.

 

[krab]

I meant free fall in the sense of weightlessness, at terminal velocity his net force will be 0. Kind of like the astronauts in space.

This is wrong. Falling through a resistive medium at terminal velocity is not free fall. If you were in a capsule falling at terminal velocity and weighed yourself (assuming the capsule not spinning), you would weigh the same as on earth. Only the first second or so, while your falling speed is much less than terminal speed is a good approximation to "free fall".

 

[lordinfamous]

So if F=ma and the Earth's gravity provides a constant acceleration then why would I die if I jump out of an airplane but not if i jump off a 10 foot ledge? I'm sorry if this is a stupid question but it's been several years since I was in a physics classroom.

its not the impact that kills you,its the sudden stop!

 

[Chi Meson]

That reminds me of...
"Guns don't kill people... bullets do"
as a humorous rebuttal to the "Guns don't kill people, people kill people" bumper sticker.

Laurie Anderson quote: "Its not the bullet that kills you, it's the hole."

 

[krab]

Similar clever-sounding silly quote. "It's not the volts that kill you, it's the amps."

 

[K.J.Healey]

Im going skydiving this saturday actually, for the first time. I hope I live.

 

[Gara]

1) Guns kill people.
2) It's not the guns that kill you, it's the bullets.
3) It's not the bullets that kill you, it's the hole.
4) It's not the hole that kills you, it's the loss of blood and failed organs.
5) It's not the loss of blood and failed organs that kill you, it's the lack of oxygen rich blood to the brain that kills you, as well as organs failing to supply oxygen, such as lungs, or blood pressure, such as the heart, that kills you.

I once said to some people that no one has ever died from being stabbed, meerly died from a loss of blood. They kinda just looked at me like and ignored me.

As for dieing from jumping out of a plane, I think the best thing to do is to try and spread the weight when you land as much as possible. Or something.

 

[Paul Wilson]

Uno Lee - "I fell down a cliff one time, I figure that it was about 10 m. In mid free fall, head first, I had the thought that I had better do something, so I somehow spun my body end for end , it must have looked like a back flip, and landed in a sitting position in a clump of vine maples with no impact. Does a spinning body land with less impact and if so why?"

Not really. I guess the aerodynams could have slowed you down a little. Think skydiving. When a skydiver goes into dive position, he/she resembles a dart and accelerates very fast, but as soon as he/she opens up into 'belly flop' position, he/she will slow down, as in belly flop you catch more air, than in dart when you are more streamline.

"It's not the fall that kills you. It's the sudden stop at the end"

When you hit the ground, your insides ripple and vibrate, causing them to rupture. The exact same happens to your brain causing instant death.

That's if you don't make a huge mess and splat.

 

[DaveC426913]

I once said to some people that no one has ever died from being stabbed, meerly died from a loss of blood. They kinda just looked at me like and ignored me.

All deaths are from the same cause: lack of oxygen to the brain.

 

[DaveC426913]

Uno Lee - "I fell down a cliff one time, I figure that it was about 10 m. In mid free fall, head first, I had the thought that I had better do something, so I somehow spun my body end for end , it must have looked like a back flip, and landed in a sitting position in a clump of vine maples with no impact. Does a spinning body land with less impact and if so why?"

The point is that hitting head-first is more likely to hurt, and more likely to injure you, because all the force of impact is concentrated on your head and neck i.e. the most critical parts of your body.

Landing on any other part of your body, especially your feet or butt not only hurts less, since they're designed to take punishment, but also they act to cushion the shock that eventually reaches your head and brain.

Spinning your body does not lessen the impact - but it sure is good advice to not land head-first!

 

[Astronuc]

Several years ago, I fell out of a tree (about 3.3 m (10ft) and landed sideways. I actually had my right elbow extended to protect my head.

The elbow hit, then my shoulder and head, then chest, then legs.

I definitely could feel tearing on my left side and compression on my right side.

I slowly rolled over and checked for protruding bones, while waiting to start breathing or lose consciousness. Since I didn't immediately blackout, I reasoned that my circulatory system, particular the aorta and pulmonary vessels, was intact.

After I got to my feet, I went inside and lay down. After I recovered enough strength enough to talk, I called my doctor. Fortunately, the internal damage was minor - lots of bruising though. Urine test didn't show any blood.

It took months to recover though.

3.3 m is about the threshold for severe injury in a sideways impact.