i got some trouble with the description of the spell physical barrier

it seems that it could be read in two ways ...
One making it a totaly unuseful spell and the other making it very powerfull..

can sombody explain to me when it does break and when it decrese in power ?

Just looking at the subject line, that would be a really great magical tradition.
"Is he a mage or a shaman?"
"Worse, he's an Argher."

If the Physical Barrier spell's Force is greater than the Power of the attack, it stops that attack cold. If the Power of the attack is equal to or greater than half of the adjusted barrier rating, the rating of the barrier is decreased by 1 - for the Physical Barrier spell, these reductions are restored at the beginning of the next combat turn.

The Physical Barrier spell is easier to take down than a normal barrier, though, because if it is merely penetrated, the spell goes down. So a shot from a 9M pistol would bring down a rating: 7 Physical Barrier spell. That barrier would stop hold-out and light pistol fire, and probably most grenades, edged weapons, and shot/flechette rounds, but yeah... I agree, it makes the spell a bit weak. At least until you get to Force levels that are hard to reach for most PCs (yeah, extra successes can also raise its power, but how many 6's do most people roll, even with lots of dice?).

If you used the rules for breaking through, instead of the rules for firing through, then the Physical Barrier spelll would be much more effective. Unfortunately, the rules seem pretty clear that you don't do that.

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