Federer Extends His Arms Away From His Body…So Maybe I Should Too?
The conservation of angular momentum means that in a spinning object not acted upon by an external force, the momentum will remain unchanged. So if we reduce the radius of movement, the object will compensate to retain its momentum by spinning faster so that its net torque remains zero.
If we flex our elbows, our racket moves faster. So given the same amount of vector force or torque a racket traveling a shorter path will move faster.
Where many get confused in tennis is the belief that racket speed is interchangeable with racket energy, or the ability to do work or move an object over a distance (in this case the rackets ability to move the ball). Racket speed is not racket power as many believe, because work done by a torque is equal to the torque multiplied by the angle of rotation. So torque is the radius of movement x force (ma) x angle between the force and lever arm.
In simplest terms:
Torque is the twisting force that causes rotation. Power is torque multiplied by rotational speed. So torque is the capacity to do work, and power is the ability to do work quickly. Torque and power are proportional to each other, but they are not the same.
So do we want to extend our racket away from our body to gain power?
Maybe.
It depends on the newton meters of force we can create and manage well. Greater speed will do work quicker, but will reduce force because it will limit acceleration.
So the goal is maximum extension which converges with maximum acceleration that can be safely managed. This distance can be experimented with and can change greatly over time. If we understand the physics here we can recognize, as coaches, that a straight arm on a forehand for example is not a panacea to correct or enhance every stroke issue.
The key takeaway is that: one size radius of swing does not fit all.
