Physics question(s)

[tinfoilhat]

Assuming a fixed right angle to the base and that the pole falls straight over, the 'safe' distance from the pole is determined by pythagoras theorem. Ie the square root of the sum of the square of the pole height + 12 the base width.

 

Haven't got the room to give this a 3m plus safety zone (although if I had my way I would;))

[Orzel]

In basic terms will a 3 metre (and after that's been worked out a 4 metre, 5 metre) scaff pole split someone's head like an over ripe melon if they are sat down 3 (or so) metres away if it's pushed over and the end of it catches them just right. I know I'm not factoring the height of the person sat (on the floor) but I'm trying to get a rough idea at this stage.

 

So simplified to 2D model that would be upside down T tipping over.

Writing all equations would be quite easy but we will be missing one important bit of data.

How much energy do you need for scaffolding pole to break through skull.

Make a mould, get some skulls, gelatin and get some more data.

[biotechpete]

Haven't got the room to give this a 3m plus safety zone (although if I had my way I would;))

 

Ah I see, so your question is how much force would it generate. Not sure I can help with that. Allegedly it takes 500kg force to crush a skull. http://www.sciencealert.com/game-of-thrones-exposed-the-science-of-skull-crushing

 

---------- Post added 09-08-2016 at 23:55 ----------

 

So simplified to 2D model that would be upside down T tipping over.

Writing all equations would be quite easy but we will be missing one important bit of data.

How much energy do you need for scaffolding pole to break through skull.

Make a mould, get some skulls, gelatin and get some more data.

 

I guess we need to know how fast the pole will fall and what it weighs to work out if it exceeds 500 kg equivalent force. 500 kg is 4903 newtons

Edited August 9, 2016 by biotechpete

[tlangdon12]

We can assume that the pole converts all its potential energy to kinetic energy has it falls until it hits a solid object. The potential energy of the pole will be its mass X the height difference between its centre of gravity (half its height) and the thing it hits X gravity. So for a 3 meter pole hitting a 1.2m heigh child the potential energy lost in the fall is (1.5-1.2)x5x9.8 = about 15 joules of energy.

 

A 4 meter pole hitting the same child will have (2-1.2)*5*9.8 = 40 joules of energy

 

I can't say what damage this will cause but I can tell you that the very best hard hats in construction are rated for 100 joules impacts. And children have softer skulls than adults.

Edited August 10, 2016 by tlangdon12

[tinfoilhat]

So simplified to 2D model that would be upside down T tipping over.

 

Essentially correct.

 

What I'll probably do is rig up something similar (morrisons had those parasol weight things for not much money) see what force is required to tip it over. I've seen mythbusters use impact pouches (or something like that) - I wonder if eBay do them?

 

---------- Post added 10-08-2016 at 00:03 ----------

 

We can assume that the pole converts alloys potential energy to kinetic energy has it falls until it hits a solid object. The potential energy of the pole will be its mass X the height difference between its centre of gravity (half its height) and the thing it hits X gravity. So for a 3 meter pole hitting a 1.2n heigh child the potential energy lost in the fall is (1.5-1.2)x5x9.8 = about 15 joules of energy.

 

A 4 meter pole hitting the same child will have (2-1.2)*5*9.8 = 40 joules of energy

 

I can't say what damage this will cause but I can tell you that the very best hard hats in construction are rated for 100 joules impacts. And children have softer skulls than adults.

 

That is awesome!!!!!

 

EDIT: I'm assuming the 5 in the equation is the 5kg weight of the pole. What's 9.8?

Edited August 9, 2016 by tinfoilhat

[Santo]

Far from sinister, quite the opposite. It sort of stems from another thread eg "it will be fine, nothing ventured nothing gained" sort of approach to my "if that goes pear shaped somebody might get killed". Long story short - sister is organising a party for my niece - Alice in wonderland I think - bro in law is trying to make things bigger and better, but not necessarily safer. Hence I've waded in with my health and safety hard hat on but I'm just uncle buzzkill rather than being able to back it up with hard science!

 

Ok, that makes sense.

 

From your posts, a base of 30 cm square for a 3 m long scaffolding pole and the masses you stated, it will be very unstable. The centre of mass of the system will be high up which means it doesn't need to lean much to fall over.

 

You need a much bigger mass for the base, or it to be spread over a much bigger area. That lowers the centre of mass, so if someone were to knock it, it would rock back onto the base rather than toppling.

 

Or, I'd be tempted to use something else instead of scaffolding poles.

 

---------- Post added 10-08-2016 at 00:22 ----------

 

The potential energy of the pole will be its mass X the height difference between its centre of gravity (half its height) and the thing it hits X gravity.

 

For the CoG it won't be half it's height because the pole is connected to a base with a 10 kg mass.

 

---------- Post added 10-08-2016 at 00:27 ----------

 

That is awesome!!!!!

 

EDIT: I'm assuming the 5 in the equation is the 5kg weight of the pole. What's 9.8?

 

It's wrong though.

 

9.8 m/s/s is acceleration due to gravity.

Edited August 9, 2016 by Santo

[yellowperil]

I think a practical demonstration might be easier and quicker than trying to get your point across with science. Just buy a watermelon and get a 3m scaffolding pole and try it.

Then ask your brother in law if he wants to sit where the watermelon was when you do it again!

How about getting a 3.5m pole and burying half a metre in the ground rather than using a base.

[Santo]

How about getting a 3.5m pole and burying half a metre in the ground rather than using a base.

 

Yeah, that's a good idea. I'd do that.

[biotechpete]

Ooh I found a paper can't link to it but it'd called

Biomechanical Examination of Blunt Trauma due to Baseball Bat Blows

to the Head

 

Says that energy required to fracture a skull is 14.1-68.5 J

 

And btw a 3m scaffold pole is closer to 10 kg in weight.

Edited August 9, 2016 by biotechpete

[tinfoilhat]

Ooh I found a paper can't link to it but it'd called

 

 

Says that energy required to fracture a skull is 14.1-68.5 J

 

Thanks for that Pete I knew I could rely on you for hard data!

 

This thread is brilliant, mainly because the first few posts didn't start with "god that's dead easy, don't you know that!!!!!"

 

---------- Post added 10-08-2016 at 00:50 ----------

 

I think a practical demonstration might be easier and quicker than trying to get your point across with science. Just buy a watermelon and get a 3m scaffolding pole and try it.

Then ask your brother in law if he wants to sit where the watermelon was when you do it again!

How about getting a 3.5m pole and burying half a metre in the ground rather than using a base.

 

That was original plan - nothing says impact more than exploding fruit I genuinely thought there would a simple answer. I'm comforted there isn't

 

I fancy s go this weekend work permitting.

 

Edit: weight of the pole was a bit of guess - but it is aluminium rather than steel I think if that's makes a difference.

Edited August 9, 2016 by tinfoilhat