Power At the Bow's Tip
To have enough power at the tip of the bow is not a question of arm
weight at all, although myriads of cellists have repeated this opinion,
which, physically speaking (not psychologically!) is simply wrong.
If you let your arm weight exert pressure in its natural weight
direction, the arm will fall towards the C-string in up-bow.
The direction of the bow pressure at the tip is not vertical to the
earth, but vertical to the string! This means that in order to exert
pressure in the upper part of the bow, you have to have a certain force
which pulls back the whole system arm/bow in a slant direction, vertical
to the string, not to the floor!
That means, that beside the necessary additional turning force of the
forearm, pressure at the tip also requires a certain pulling back-force,
transmitted by a wrist activity called "adductive". This force pulls, in
the case of the bow arm, a little bit (seen from the player) towards the
left. The mere turning of the forearm would only exert pressure in the
direction towards the earth.
Try it! You will be surprised about the easy additional force you get as