Impact Speed

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Magnus effect is really applicable in ballistics to any degree in anything other than a hurricane crosswind.

In ballistics where the spin is along the axis that the projectile is travelling - agreed.

When spin along the axis perpendicular to travel or along the vertical axis you see it's effect quite soon. Either that or my golf game needs work on basic aiming.
 

Licramite

Über Member
Location
wiltshire
not really wanting to get involved in this again, but it occurred to me that maybe you were looking at the wrong forces, - you were interested in speed, but maybe you should be looking at G force.
The brain sustains damage within the skull at impacts of 10G upwards - isn't that the important factor not how fast your head hits the ground ?

now we have established the speeds involved - just need some clever dicky to convert that to Gs -
heres a starter for 10.
1G = 9.812m/s/s , 1Newton = 9.812Kgm/s/s

any takers ?
 

Hawk

Veteran
not really wanting to get involved in this again, but it occurred to me that maybe you were looking at the wrong forces, - you were interested in speed, but maybe you should be looking at G force.
The brain sustains damage within the skull at impacts of 10G upwards - isn't that the important factor not how fast your head hits the ground ?

now we have established the speeds involved - just need some clever dicky to convert that to Gs -
heres a starter for 10.
1G = 9.812m/s/s , 1Newton = 9.812Kgm/s/s

any takers ?

You're right, acceleration is what causes forces that can cause harm. If you jump off a building, you're perfectly fine when flying towards the ground at 50mph, until the ground meets you and imparts a force on you...

However, the average force required to bring you to a stop in a certain distance varies inversely with speed:

acceleration, a = (final speed^2 - initial speed^2) / 2s where s is the distance travelled from when the force started acting, at the initial speed.

If you work out a using the above equation (measuring s can be tricky), you can figure out a force. If you want it in g, just divide a by 10ish
 

green1

Über Member
Deceleration is the important factor yes and it depends on the speed you were travelling and the distance over which the deceleration occurred.
The head can withstand more than 10G by the way, otherwise anybody who has used an ejection seat would be a vegetable, the old Russian seats were about 22G.
 

Licramite

Über Member
Location
wiltshire
Injury to the brain starts at 10g and ranges up to 50g.
chances are the Russian pilot would suffer some brain damage on using an ejector seat.
its estimated 60% of brain injury goes untreated
30% of troops coming back from Iraqi had minor brain damage from the effect of blast.

most of us have had some minor brain trauma in our lives.
I checked the symptoms for minor brain damage and I certainly have suffered some brain damage at some time in my life (that or its early Alzheimer's) - but when I think back to what I did in my younger days I'm not surprised.

this is what drew me to the conclusion measuring the G force would be more worthwhile than measuring the speed of impact. - from a human point of view. not for designing machines ect.
 

srw

It's a bit more complicated than that...
Since the G-force is just a function of speed of impact (highly variable) and time to decelerate (almost constant), the speed of impact is the most important consideration.
 

StuartG

slower but no further
Location
SE London
Since the G-force is just a function of speed of impact (highly variable) and time to decelerate (almost constant), the speed of impact is the most important consideration.
Neil Armstrong lived a long and academically fulfilling life. If the rigors of test plane flying, ejections and the occasional Saturn V burn eventually did for his body then it was the heart that gave out first. This pattern seems to be reflected amongst his cohort. Whereas my childhood hero died from the progressive effects of frequent head impacts. He was a WBA striker. Indeed many of today's footballers appear to be a bit lacking in the brain department. Hmmm another sport we should be compelling helmet use? And don't get me onto professional boxing ...
 

Licramite

Über Member
Location
wiltshire
I think we established the horizontal speed doesn't effect the vertical speed , so on splat calculator a 10stone person falling 1.6m off his bike hits the ground in 0.55seconds @ 5.6m/s = 20.16kmh = 12mph with 1176joules of force.
here I get fuzzy to convert joules to newtons , 1176 div by kgmass of 70 = 16.8Newtons , which gives us a G of 16.8 ? - which looks about were I would expect it to be, but please be happy to shoot me down in flames at this point.
 

Licramite

Über Member
Location
wiltshire
of course your right, I only ignored it as I couldn't calculate it.
I am trying to find that initial point of impact - if we have two forces , the horizontal one (your forward speed) and a vertical one - (your fall). put together your travelling down a hypotenuse of a triangle. but they are independent.
so you cannot add them together but both are happening at the same time, would it be fair to say in that case you take the greater force - which would be the 20mph horizontal force ?
if that was so you would be looking at an impact of 28G. (12mph=16.8g, 1mph = 1.4g x20)
 

srw

It's a bit more complicated than that...
The initial calculation assumes that the force of the decelaration of the entire body is directed through the point of impact. I suspect that's not true - some (probably quite a lot) of the force will be dispersed through the joints of the body. The only bit of mass that unambivalently gets decelerated by the surface hit is the mass of the head.
 

green1

Über Member
of course your right, I only ignored it as I couldn't calculate it.
I am trying to find that initial point of impact - if we have two forces , the horizontal one (your forward speed) and a vertical one - (your fall). put together your travelling down a hypotenuse of a triangle. but they are independent.
so you cannot add them together but both are happening at the same time, would it be fair to say in that case you take the greater force - which would be the 20mph horizontal force ?
if that was so you would be looking at an impact of 28G. (12mph=16.8g, 1mph = 1.4g x20)
You'd hit the ground at 22.5mph at angle of 63 degrees from vertical. I've know idea where your getting '28g' from. 1 'G' is 9.81ms^-2, 28 'G' is 275.7ms^-2.
 
Not entirely related, but I read somewhere that in a direct collision in a car,assuming you have your seatbelt on, it's not the collisional force forward that kills you. Your body flies forward, the seat belt pulls you back, then in a pendulum motion, your internal organs then fall forward again (the third motion) and it is often this that causes the internal damage that can kill.
 
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