His Excellency Aethien wrote:
Hey, I'm no scientist.
Also, apparently I was wrong about the speeds. A little googling says that keepers train with machines set to 140km/h to get a speed comparable to the hard hitters on penalty corners so assume 125km/h instead of 100. And does it matter how flexible the ball is (or whatever the proper terminology is)? a baseball gives quite a bit when you hit it with a bat, a hockeyball is just hard plastic so that probably doesn't budge.
For lack of a better term, the resistance of the object to a change in shape can be reasonably modeled in the duration of impact. A beach ball, for example, changes shape easily, so the impact is longer. Thus, less force involved in the impact.
This is totally spit-balling, but assume duration of impact is 1/20th of a second. That means that, in effect, your body is pushing on the ball hard enough to slow it down from 125 km/h to 0 km/h in .05 seconds.
velocity = ~35 meter / second
mass = .16 kg
momentum = m x v = 5.6 kg x m/s
Average Force = (change in momentum) / (change in time) = 5.6 / .05 = 112 Newtons of force.
Based on an article by Scientific American
, a professional boxer generated about 3.5 times as much force (400 newtons), while the average untrained person was estimated at 1/3 the force (10% of the boxer, or 40 newtons). In other words, It's not like getting into the ring with a heavy-weight boxer, but it's a lot harder than your buddy can punch you in the arm when you see a VW driving down the road.
One source said that ~30 joules of energy can break a rib, so your hockey ball well exceeds that. I couldn't tell if that figure was modeled using a "dry" bone, or tested using a cadaver with all the tissue around it to alter the impact. Edited, Aug 9th 2012 8:12pm by AstarintheDruid