General / Off-Topic Who gets hurt more? [OOC]

[Red Fox Four]

(why is there no off topic forum in these forums?)

Anyways, I'm trying to enlist some help in crosschecking if the conclusion at the bottom is true, based on the math.

Scenario: Kid fell off the slide in the playground from about 1.5m up.

Claim: Wife scolds the husband stating that a child falling from 1.5m would be equivalent to an adult falling from a rooftop.

So is this really true?

Assumptions for sake of proving a point: The kid is around 20kg, an average adult is around 80kg.

The potential energy (PE) a kid with a mass (m) of 20kg has at a height (g) of 1.5m would be PE = gmh ... ergo 9.81 * 20 * 1.5 = 294,3 Joules of Energy. That means when he falls that potential energy is converted to kinetic energy and he hits the ground with a force of 294,3 Joules.

The potential energy (PE) an adult with a mass (m) of 80kg has at a height (g) of 1.5m would be PE = gmh ... ergo 9.81 * 80 * 1.5 = 1177,2 Joules of Energy. That means when he falls that potential energy is converted to kinetic energy and he hits the ground with a force of 1177,2 Joules.

So comparing the ratio between the two, 1177,2 / 294,3 = 4, this means the adult will hit the ground 4 times harder than the kid when dropped from the same height.

Turning this around a bit we can then also say that adults energy of 1177,2 = 9,81 * 20 * X ... solve for X we get X =1177,2 / 9,81 * 29 and X = 6.

In other words... for a kid of 20kg to experience the same energy that an adult falling from 1.5m does the kid would have to fall from 6 meters.

So my conclusion is: It hurts more for an adult to fall 1.5m than it does for a kid... and we don't have to worry about kids falling down from something unless they fall from a 3rd floor window or higher.

 

[joshman72nd]

depends on what you land on...

alot of places i take my little cousins have bark around the play ground now/growing up i landed on small smooth rocks.

now if i fall i land on tree branches or concrete either way im not getting out of it without at least a bruise and a couple cuts/scrapes

 

[babelfisch]

https://forums.frontier.co.uk/forumdisplay.php?f=17

 

[Ouberos]

Please tell me it's your kid and you spent twenty minutes doing this rather than consoling child? That would be quite funny.

(From an uninvolved observers point of view)

 

[Red Fox Four]

depends on what you land on...

alot of places i take my little cousins have bark around the play ground now/growing up i landed on small smooth rocks.

now if i fall i land on tree branches or concrete either way im not getting out of it without at least a bruise and a couple cuts/scrapes

Well it's sand. Anyways, the energy when you land is still the same though nomatter what you land on. And since both an adult and a kid would land on the same type of surface you could argue that the type of surface is irrelevant when considering who lands hardest. It is relevant if you consider "does it hurt to fall from 1.5m".. then you can say "depends what you land on" as landing on a comfy bed would not hurt, but landing on concrete with a bunch of cutaway rebar sticking out would potentially be lethal.

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Please tell me it's your kid and you spent twenty minutes doing this rather than consoling child? That would be quite funny.

(From an uninvolved observers point of view)

No, it's not my kid. It's a friends kid. He was getting scolded and I was curious if his wife was right.

I think that she was wrong though. At least that is what I get from the math (thus far), unless there is something vital I have left out.

 

[snadge]

Without even doing the maths it is blatently obvious that your friends wife is an idiot.

 

[dayrth]

You would also have to take drag into account. The kid (being smaller) would have a grater surface area to mass ratio than the adult so would experience more drag. (Would also have a slower terminal velocity, but that would not factor in to such a short drop).

Even better news for the kid

 

[Red Fox Four]

Without even doing the maths it is blatently obvious that your friends wife is an idiot.

I'd rather state that she was more of an upset mom than an idiot. Arguably you could say my friend was the idiot for not watching his kid and letting him fall down in the first place.

However, we could also argue that based on the math it doesn't matter if the kid falls down from 1.5 meters since we know that an adult falling from such a height would hurt himself a little but it wouldn't be much... and the maths above dictate that the kid would hurt himself 4 times less than an adult falling from 1.5 meters.

In fact, the kid falling from 1.5m wouldn't hurt more than an adult falling from PE = gmh ... 294,3 = 9,81 * 80 * X... solve for X and you get X = 294,3 / 9,81 * 80 .. X = 0,375 ... ergo the kid falling from 1.5m would hurt the kid as much as an 80kg adult falling from 0,375m, in other words 37,5cm.

I guess that is why we say "kids bounce back" when they fall from low heights between 0 to 6 meters.

 

[Miko_Stargazer]

Your math is correct and the adult would have 4 times the impact energy because they have 4 times the weight. The only only factor would be impact 'resistance.' Obviously a newborn child is at far more risk from such a fall, but I think there's a good argument that toddlers are even more resistant to falls than adults.

The mother in question is probably thinking that because the child is smaller and the distance the child fell is larger proportional to its body that it equates to a larger impact.

 

[Red Fox Four]

You would also have to take drag into account. The kid (being smaller) would have a grater surface area to mass ratio than the adult so would experience more drag. (Would also have a slower terminal velocity, but that would not factor in to such a short drop).

Even better news for the kid

Well, the velocity upon impact for both adult and the kid would be the roughly the same given the short distance and the fact that mass doesn't affect the velocity of something falling in free-fall.

They would both be subject to 5.422m/s velocity upon impact *edit* (based on falling from 1.5m and subject to 9.81m/s gravity)

 

[Jack Schitt]

If you really want to dig deep into this sort of thing you'd not only have to factor in physics but also biology and maybe even diet and lifestyle. At which point you'd have to do a statistical study and start to introduce probabilities. But the main point is that you're arguing with a mother, in a scenario that involves her child. Which means she's always going to be right and not even Hawking could maths his way out of that.

 

[Red Fox Four]

If you really want to dig deep into this sort of thing you'd not only have to factor in physics but also biology and maybe even diet and lifestyle. At which point you'd have to do a statistical study and start to introduce probabilities. But the main point is that you're arguing with a mother, in a scenario that involves her child. Which means she's always going to be right and not even Hawking could maths his way out of that.

"Not even Stephen Hawking could maths his way out of an argument with a mother".

Hilarious

And yes, this may call for further study and experimentation.

First we need to acquire mothers willing to throw their 20kg kids from a 6 meter (that's 19 feet 8 inches to you non-Metrics) tall building to measure the energy of the impact and study the resulting biological effects.

 

[Lunchmoney]

(why is there no off topic forum in these forums?)

Off topic forum --> https://forums.frontier.co.uk/forumdisplay.php?f=18

 

[Dakron Nova]

No, it's not my kid. It's a friends kid. He was getting scolded and I was curious if his wife was right.

I think that she was wrong though. At least that is what I get from the math (thus far), unless there is something vital I have left out.

As someone who has been married 20 years, and speaks with some experience of interacting with the opposite species.

I would strongly suggest that you sit down with your friends wife and take her through your workings, as they look spot on to me. Im sure she will act logically and rationally and thank you for all your hard work and the effort you have put in.

 

[Ian Phillips]

Moved to off topic

 

[Red Fox Four]

As someone who has been married 20 years, and speaks with some experience of interacting with the opposite species.

I would strongly suggest that you sit down with your friends wife and take her through your workings, as they look spot on to me. Im sure she will act logically and rationally and thank you for all your hard work and the effort you have put in.

I sense a hint of sarcasm... perhaps not sarcasm as much as... "Do it... go ahead... do it... I dare you!"

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Moved to off topic

Thanks Ian!

 

[Troy_McClure]

I agree with the drag factor being the main issue here..if the guy was dressed as a woman when he fell off the roof, the dress would act as a parachute

 

[Red Fox Four]

I agree with the drag factor being the main issue here..if the guy was dressed as a woman when he fell off the roof, the dress would act as a parachute

Well if an 80kg adult fell from the roof (6 meters ~ 19-20feet) the energy on impact would be 4708.8 Joules. For a 20kg kid to experience the same energy on impact the kid would have to fall from 24m ~ 78-80feet.

At those distances then yes, wind resistance and drag becomes a factor.

Falling 1.5m though the effect of drag is so small as to make no significant difference and thus I ignored it.

 

[Dakron Nova]

I agree with the drag factor being the main issue here..if the guy was dressed as a woman when he fell off the roof, the dress would act as a parachute

Oh wait....we can land on atmospheric planets now?

 

[BACKER #-4112]

As a kid, I used to jump off the roof into a metre deep snow. When the snow melted I kept jumping off, landing on my feet.
I would never dare to DIVE off head first. At a child age, we healed quicker and our bones were still developing.
As a grownup, I wouldn't dare to try the same jump. Bones being brittle and not being as flexible as a child, chances are I
would pull a muscle or a tendon and a broken bone would take a lot longer to heal.
So I guess if the child fell and landed on his/her feet or "bum" (that's not the word I had in mind but "family forum"...)
then big whoop, shut up mom. But the chances are the kid could have landed on his/her head (even from a half a metre height)
and the weight of the body could have injured the neck, turning the kid into a redacted.
I guess that scenario warrants a mothers reaction.

<snip> I guess that is why we say "kids bounce back" <snip>

I am willing to try this out but I don't have a kid. If a parent is willing to lend me one, along with a signed consent form,
nah, I am just messing around now... Welcome to the Off Topic Thread, hope you enjoy your stay.