B How do I express the force of me falling 33 feet onto concrete?

[pushcart]

I weight 90.7kg. I fell 10.05m landing on soild concrete. how do I express the "power of my impact? in G-force? A relitive weight? I am self taught in very basic physics after a high school education.

 

[fresh_42]

You have to calculate your velocity at the end of the fall, possibly under consideration of air resistance, then measure how thick you are, depending on the angle at which you contact the ground. Then you get the acceleration between this velocity and zero, divided by the time your backside or head needs to reach your frontside or, say pelvis. These will still be estimations because you cannot really know how long it takes to come from a given velocity to zero in order to measure the acceleration in $g$.

 

[pushcart]

thank you fresh_42. I landded on my side, so my center of mass was 6in from ground on impact with concrete. but do I understand you correctly that the measurement I'm looking for is G force upon impact? As a way to measure layman term hit the ground

 

[berkeman]

I weight 90.7kg. I fell 10.05m landing on soild concrete.

Ouch. Were you rigging a stage when this happened? Did you break anything and/or need a ride to the hospital? That's a pretty significant fall.

And as @fresh_42 is alluding to above, the "force" of impact is usually expressed as an "impulse", which is change of momentum (mass X velocity) versus time. The higher the mass and velocity and the shorter the duration of the impact, the higher the impulse (which is what does most of the damage).

https://en.wikipedia.org/wiki/Impulse_(physics)

 

[pushcart]

Fortunately it was early in the day while hanging speakers so no crowd and yeah I was unconscious for two hours woke up in an MRI machine I smacked the ground pretty darn hard.

 

[pushcart]

Ouch. Were you rigging a stage when this happened? Did you break anything and/or need a ride to the hospital? That's a pretty significant fall.

And as @fresh_42 is alluding to above, the "force" of impact is usually expressed as an "impulse", which is change of momentum (mass X velocity) versus time. The higher the mass and velocity and the shorter the duration of the impact, the higher the impulse (which is what does most of the damage).

https://en.wikipedia.org/wiki/Impulse_(physics)

Ok, that makes sense. So the variable that I don't have, but can estimate is the time it took to change my momentum from falling speed to zero, "impulse"

 

[berkeman]

Ouch. Glad that you're okay now. Falls like that are no fun (I work part-time as a medic in addition to my full-time EE work, so I've worked on patients who've done what you did).

 

[pushcart]

That day I didn't respect physics about 20 feet away in the trunk of my car was all of my safety equipment harnesses ropes helmet. But I figured hey it's only 33 feet done it 1000 times. I broke all sorts of stuff, learned to not ever do that again

 

[pushcart]

Ouch. Glad that you're okay now. Falls like that are no fun (I work part-time as a medic in addition to my full-time EE work, so I've worked on patients who've done what you did).

On the upside I physically proved that gravity is not a theory that is proven physics

 

[fresh_42]

On the upside I physically proved that gravity is not a theory that is proven physics

I hope you mean the movie.

 

[jim mcnamara]

To save you some effort, try: https://www.omnicalculator.com/physics/free-fall

 

[pushcart]

I hope you mean the movie.

OK that was funny

 

[pushcart]

To save you some effort, try: https://www.omnicalculator.com/physics/free-fall

thank you my friend that was the exact calculator I was looking for

 

[fresh_42]

To save you some effort, try: https://www.omnicalculator.com/physics/free-fall

Thanks. Added.
https://www.physicsforums.com/threa...h-physics-earth-and-other-curiosities.970262/

 

[berkeman]

But I figured hey it's only 33 feet done it 1000 times.

Highest fall I've treated was a 20 y/o female who was dancing on the rooftop of a warehouse in Oakland a couple years ago at a music festival (no, they were not supposed to have climbed on top of the warehouse for a better view of the stage). She was a bit, um, impaired, and managed to fall through a glass skylight 50 feet to the bare concrete floor below. My partner had to scale an 8-foot fence and break a window to get into the warehouse (and let the rest of us in), and we worked on her for about 10 minutes until the ambulance crew could get the gurney through the festival crowd and into us.

She had broken ribs, a collapsing lung, in and out of consciousness and a few other less important fractures. She survived, but if my partner hadn't been so quick to get in there and let us in, there's a good chance she would have died because of the lung going down.

(My partner that day is now in the Navy -- she is currently on an aircraft carrier at sea, working as an Air Traffic Controller).

 

[pushcart]

Highest fall I've treated was a 20 y/o female who was dancing on the rooftop of a warehouse in Oakland a couple years ago at a music festival (no, they were not supposed to have climbed on top of the warehouse for a better view of the stage). She was a bit, um, impaired, and managed to fall through a glass skylight 50 feet to the bare concrete floor below. My partner had to scale a fence and break a window to get into the warehouse (and let the rest of us in), and we worked on her for about 10 minutes until the ambulance crew could get the gurney through the festival crowd and into us.

She had broken ribs, a collapsing lung, in and out of consciousness and a few other less important fractures. She survived, but if my partner hadn't been so quick to get in there and let us in, there's a good chance she would have died because of the lung going down.

(My partner that day is now in the Navy -- she is currently on an aircraft carrier at sea, working as an Air Traffic Controller).

Wow. I'm a bit of a weirdo'cause I was very disappointed I missed the whole ambulance ride and everything because I was out cold, lol. Paramedics, are truly my heroes

 

[sophiecentaur]

And as @fresh_42 is alluding to above, the "force" of impact is usually expressed as an "impulse", which is change of momentum (mass X velocity) versus time. The higher the mass and velocity and the shorter the duration of the impact, the higher the impulse (which is what does most of the damage).

Impulse is a very useful quantity to use in many mechanical interactions but calculating the force from Impulse involves actually knowing the time taken for a collision. I would guess that the better way to approach this sort of question would be in terms of Energy or Work Done in 'absorbing' Kinetic Energy of the falling object. Work done is Force times Distance (in the direction of the Force). To calculate the time involved (working with Impulse), you'd need to have been there at the time, with all sorts of measuring equipment.

Using the quantity Work, you can estimate the Force in terms of distance traveled by an object whilst coming to a halt. So, in the case of a head-on vehicle collision, the passenger would be subjected to a huge maximum force when colliding with the stationary, rigid windscreen but to much less force when an air bag extends the braking force over several tens of cm. (I really can't suggest the actual quantities of Forces involved but they will / could vary a lot over the body after a fall from height)
Start with the Energy of the body (say 80kg mass) falling from 10m. That's mgh=8000J.

Landing flat on the ground, the damage done to various parts of the body would depend on which bits landed first. If you hit, legs first, then your could have traveled almost a 1m, slowing down all the time(at the expense of your legs) to almost zero. The Force on the rest of the body whilst being slowed up by the legs would be 8000/1 = 8000N which is ten times the normal weight! That's equivalent to 10g, which is extreme but survivable (legs can be repaired).
As a rule of thumb, you could say that (from a fall of 10m - makes the sums easy), the g force on parts of the body would be 10/ (deceleration distance in m).

Lucky to survive imo. Glad the OP can talk about it!

 

[Herman Trivilino]

So the variable that I don't have, but can estimate is the time it took to change my momentum from falling speed to zero, "impulse".

The change in momentum from falling speed to zero is equal to the impulse. From there you can calculate the average force of impact using your estimate of the time.

 

[jbriggs444]

Rough estimate for landing acceleration is, per the approach by @sophiecentaur quite simple:
$$a = g \frac{\text{drop distance}}{\text{crunch distance}}$$

 

[fresh_42]

I think it is time to close this morbid discussion now. If necessary, we can debate free fall, air resistance, elastic and inelastic collisions with less drastic examples.

Thanks for your participation.