Beside the acoustical
effects of the lightning there are noticeable mechanical effects. It
is noticed that strike can damage a part of some building (roof, chimney
destroy a tree or some wooden post but that is not all. It is noticed
that some metal parts that conducted the lightning current were damaged
and misshapen. It means that when we talk about the current of lightning
we must pay attention to its mechanical effects that can be very important
in certain circumstances.
It is determined that the force can be caused by two reasons. First
reason is a great enhancement of pressure that happens when lightning
passes trough some media and heats it. That pressure is especially destructive
when it is caught in some closed area, not in the open air. If lightning
current passes through some crack in the wall of the house, pressure
increases so those walls can't stand that. It especially happens if
those cracks are humid and water in them transforms into steam. Same
thing happens if lightning current is passing through the capillary
of some tree. Usually the pressure is very high and the tree explodes.
reason for appearance of force is purely electromechanical. When current
passes through some metal part put in magnetic field, mechanical force
acts and "tries to pull the part out of the field". Force
can be determined from next expression:
P = B * ig * l
P stands for mechanical force,
B stands for magnetic induction (magnetic field),
ig stands for current and
l stands for length of the conductor.
is also known that every current produces its own magnetic field. For
example if current passes through two wires not far one from another,
every wire produces its magnetic field and every wire is in the field
made by another wire. It means that mechanical force appears and affects
both wires. Direction of force depends on directions of currents in
For example, if the currents are parallel and have the same direction,
than the force is trying to separate them. Oppositely, if currents are
parallel but have the opposite direction, than the force is trying to
bring them close to each other.
force can be determined from this expression in wich P stands for force,
uo stands for
permeability of media between wires, ig stands for current, a stands
for distance between wires and l for lebght of wires.