This is following the Mage 20th Aniversary Edition rules.
Well, one of my players has a Mage with forces 5 and life 1 (only that, no more points in other spheres). The thing is that he has asked if he can change the movement vectors from living things, to do such things like changing the direction of movement so he can break limbs, throw cristal balls as bullets or maybe using the blood to explode someone's body.
Is this even possible?
Note: Given the clarification in the question's comments, the specific character breaks the rules. However, the combination of spheres is possible.
This question highlights the divide between mechanical effects and special effects.
Mechanically, Forces 5 can bring immense and varied power to bear on the targets of the angry mage. The Forces Master brings the potential to inflict ridiculous damage on her foe. Which is pretty much true of every Master. If you just say "I used Forces 5 to kill my target" and then roll well enough, the target is dead.
There's no reason a a clever player can't get creative with the special effects. In fact, not doing so would be pretty dull. Some effects might use other Spheres to help guide her invisible hand, but the Forces is the primary agent of change here.
changing the direction of movement so he can break limbs
With Forces 5 and enough kinetic damage/shearing force, broken limbs are already a consideration. Life 1 could be used to help a mage target specific limbs. As in "I break the man's gun-wielding arm with precisely applied shearing force."
To break a limb, Forces 3 Life 1 and enough Lethal damage to break the limb. Say... three levels. If you're targeting this specifically, extra successes probably wouldn't do more damage.
throw cristal balls as bullets
Forces 2 is all that's needed to move the crystal ball, per the chart on Page 509. Still need enough successes on the roll to simulate 'bullet' speeds. Say... three successes?
or maybe using the blood to explode someone's body.
You'd definitely need Life, and more than 1, to make the blood in a body move. But you can still achieve the special effect of an exploding body. I'd call this a special effect of applying enough Lethal Forces damage to kill the target outright. Basically the effect is "rapidly superheat the target," and the roll would determine it's efficacy. Probably 5 successes to actually explode the target, but 4 successes on this roll would instantly kill most people as all of their blood and organs cook at once.
And then I'd apply paradox. Hope it was worth it. :)
There was something bugging me about this question and after a careful re-reading of the 20th anniversary rules it appears that your player is not following the rules as they are not meant to have a Sphere rating higher than their Arete.
This is first mentioned in character creation on p258 under 'Spheres':
Your beginning Sphere ranks cannot be higher than your character's Arete rating.
and again on p330 under 'Game Effects of Arete':
Your Arete also defines your magick's potential. You cannot have a Sphere ranked higher than your Arete rating
I don't know if this rule comes from earlier editions but it is definitely one that is there to prevent problems like the one that you are experiencing - minmaxing of the rules by overenthusiastic players.
p.s. Page numbers refer to my PDF copy of the 20th anniversary rules, they might be different in other versions
Manipulating "movement vectors" is certainly possible with Forces 5. The crystal ball trick and the arm trick are totally valid, provided the objects are already in motion. However, the blood trick would require Life 3 — that's basically Rip the Man Body.
