Technical term used in physics and engineering; often interchangeable with 速度 (そくど) but carries a more formal or scientific tone.
この実験では、物体の速力度を正確に測定する必要がある。
In this experiment, it is necessary to accurately measure the velocity of the object.
速力度と速度は、物理学では厳密には異なる概念だ。
In physics, speed and velocity are strictly different concepts.
Compound of 速 (speed) + 力 (power) + 度 (degree). The exact historical derivation is uncertain; it appears to be a technical coinage for 'velocity'.