Can someone explain the physics behind catching a falling person?

I sometimes read news articles about babies or small children being dropped from burning buildings and caught by bystanders. I’ve always wondered what kind of forces are at play here? I’m assuming Newtons Third Law of Motion is the starting point?

This guy caught an adult woman. How was this guy able to walk away with just deep bruising on his arms? Say the lady’s mass was 130lbs. She dropped 50ft. What kind of forces did this guy absorb? Was he just lucky not to get killed? How does his mass factor into this? Would a smaller guy get hurt worse? How much was the woman’s impact negated by getting caught? I’m guessing the fall would have killed her otherwise?

How about a 22lb baby dropped 50 ft and caught by someone? Thats more common than catching an adult. What are the forces and impact here?

I vaguely recall force calculations in Physics classes thirty years ago. Diagrams with arrows. But thats about it. :stuck_out_tongue:

Don’t think it possible to say precisely as it partially involves her velocity, which coud vary due to a number of things, even including the clothes she was wearing and her physical attitude when she fell. He alo may not have caught “all” of her – for instance, he might have absorbed the weight of her falling head and shoulders, but her legs and part of her trunk may have fallen practically unimpeded to the ground.

Force vectors. That’s the term I was struggling to recall. :wink: Not force calculations.

Good point Boyo Jim. I hadn’t considered a partial impact.

I don’t know the formulas to use, but I think it would be something like this:

1 - When something falls 50 ft, how fast is it going?
2 - At that speed, how much deceleration is needed for it to stop in 3 feet or so?
3 - How can you express that deceleration in terms that a layman can relate to?

He didn’t actually catch her. He broke her fall so she didn’t hit the ground as hard as she would have without his help. According to this article, she bounced off him before hitting the concrete. I don’t think there’s any way someone could catch a normal-sized adult who had fallen that distance.

He could have been killed. If the woman had knocked him down so he hit his head, or she hit him in such a way that she landed on top of him, his injuries would have been much worse.

Just did that over here.

After a 50-foot fall, the velocity will be 38.7 MPH. Aero drag won’t be signfiicant at these low speeds.

For an object that has just experienced a 50-foot freefall at 1 g, slowing it to zero in a 3-foot distance will result in 50/3 = 16.7 g’s. of deceleration. For a 130-pound woman, this means 2167 pounds of force.

The catcher would only have been able to exert a very small portion of this with muscular activity; the rest of the decel would have been simply by absorbing impact with the mass of his body. Given that she was critically injured and he was also somewhat injured, it seems certain that only the life-critical parts of her body (head, torso) were slowed (not stopped) by him, and the rest (legs, lower body) probably hit the pavement pretty damn hard.

Someone catching you won’t do much to improve your prospects in a fall, and is likely to just end up with both of you injured. The problem with impact after a fall is always to maximize your stopping distance, and either way, your stopping distance is going to be more or less the length of one human body.

This always bothered me in Superman movies. Lois is falling (for the umpteenth time) and superman races up to catch her… which should result in Lois soup in Superman’s arms.

Souper Man?

Uses his Superdeceleration power.:smiley:


You see this in action movies all the time. Iron Man is another good example. He’ll lose thrust for some reason and plummet to the Earth, but stop himself just in time. No. He would slam into the inside of his suit and die.

Spiderman does this with people as well.

Although, to be fair, it didn’t work out so well for Gwen Stacy.

There’s also the question of where the energy goes. I’d certainly rather fall horizontally on a 3-foot foam mat than vertically, using my lower body to absorb the energy (and risking cracking my skull on the pavement). Using a squishy human as a mat isn’t optimal but it’s probably better than nothing.

Humans, properly secured, can be safely accelerated at 50 gees. With the right cradling, someone could easily survive a 50 foot drop with a single foot of deceleration. It’s the cradling (or lack thereof) that’s the limiting factor.

Aha! Questions I can answer. :slight_smile:
I’ll share my calculations if people want, but I figure most folks who could follow them don’t need them.

  1. falling 50 feet (ignoring wind resistance and stuff) you will be going about 56 feet per second, or 38mph.
  2. stopping in 3 feet would be decelerating at 18g.
  3. It should knock you out. It probably won’t kill you (NOTE: that’s just the deceleration. Whacking your head against the ground is a separate issue.)

What’s at work here, though, is that people are squishy.
Perhaps a better layman’s terms for the experience is to imagine an Olympic sprinter running into you at full speed. This hit was a bit harder than that.
But from her end, landing on a guy is WAY better than landing on concrete or chairs.

They did this on The Vampire Diaries last week. Someone jumped from a clock tower in a suicide attemp and a vampire intervened by catching her while he stood on the sidewalk below. The show’s vamps have been shown strong enough to handle such forces, but a regular person jerked to a stop? Not so much…

You joke, but that’s pretty much the explanation. He supposedly has this force field surrounding his body that can absorb the energy of impacts without imparting that energy back to the object. He can also extend this forcefield around objects, which is why he can lift large objects without them breaking. And this is all instinctual.

As for where the energy goes? My guess is that it’s converted to heat, or perhaps used to charge Supes’s “solar battery.”