It is the circular motion in Aikido that allows the art to be efficient and effortless. It deploys maximum effect with minimal precise effort.
An attack is not stopped or halted but rather deflected with circular motion. Ukes forward momentum combined with Nage's accurate rotation takes balance. Ukes center does not have to be moved very far to create instability.
Once balance is taken uke becomes very light and easy to redirect. Uke is compelled to move where he is led.
We study and can spend years developing an intuitive sense in regards to the relation of force, timing, and rotation. Correct delivery of these components results in the power and grace that we see in aikido techniques.
And underneath it all lies a peaceful calmness with a very grounded and energized sense of center.