The mechanical properties of a projectile
depends on its speed. For example, if I take a soft lead bullet and press it
slowly against a steel plate, say 0.5 cm thick, using a mechanical press, it
would deform into a lead disc and the steel plate would be largely
unaffected. However, if I take the same soft lead bullet and it's fired from
a 0.357 Magnum, it would easily blow a large hole in the same steel plate.
The difference is that deformation of a projectile takes a certain amount of
time to occur. If the impact time is very short compared to this
characteristic time of deformation, the mechanical properties of the object
will be very different. This is not an uncommon phenomenon. Another example,
if I jump into a lake from a height of 1 meter, I just sink and make a
splash -- no harm. But if I jump into the same lake from an airplane at 1000
meters above the surface, I'm a pancake. I might just as well hit solid
ground. The reason is: at the speed with which I hit the water is so fast,
the water does not have time to "get out of the way" so it becomes
essentially a solid. This is what happens to straws etc. driven by tornadic
winds. They become projectiles, like an arrow.
