On Sun, 08 Jul 2007 01:23:09 -0500, Tim McNamara
>I haven't got a bowling ball. Maybe we can get Fogel Labs to give it a
>try and video the results. Anybody got an old undamaged helmet or two
>to send to Carl?
Fogel Labs has no bowling equipment, but the experiment probably isn't
A head inside a helmet is practically guaranteed to fit without
putting spreading pressure on the sides of the helmet.
Heads are longer than they are wide--look at any reasonably
well-fitting stiff hat. (Soft caps simply bend to fit the noggin.)
In contrast, a bowling ball is round. If large enough, it should
easily crack a typical bicycle helmet against the floor by acting as a
Most bicycle helmet manufacturers recommend replacing any helmet
dropped on the ground, since they crack easily. Fewer and fewer
bicycle helmets pass even the watered-down recent tests, none of which
ever matched the force of a six-foot rider toppling over sideways
after forgetting to unclip at a stop light.
Curiously, toppling over sideways (as opposed to a free fall drop)
produces a greater acceleration and impact for the end (or head) of
the thing toppling.
(This is why tall chimneys break as they fall. They're not stiff
enough to accelerate the upper part without breaking. Think of a
felexible rod--the end lags behind if you wave it.)
As others have calculated in earlier threads, the far end of a
toppling board hits the ground at 3/2 or 150% of the speed it would
strike if dropped in free fall from the same height.
Since kinetic energy for the same mass increases with the square of
the velocity, this means 9/4 or 225% of the original impact energy of
An object (such as a severed head in a helmet) dropping free for the 5
feet often mentioned will hit the ground at 17.93 feet per second, or
The same object falling over sideways on a pole (closer to how heads
actually hit the ground when bike frames are between legs) will land
at 3/2 that speed, about 27 feet per second, or 18.4 mph.http://hyperphysics.phy-astr.gsu.edu/hbase/traj.html
Given the flexibility of the human body, actual impacts should be
somewhat less than the rigid-pole example, but still noticeably
greater than free fall.