From what I understood, both 速さ{はやさ} and 速度{そくど} means "speed". Some say that they are synonyms (just like speed and velocity in English), but I guess there is a nuance between them, isn't it ?
速さ{はやさ} comes from the adjective 速い{はやい}, like other adjectives (長い{ながい} : 長さ{ながさ}, 深い{ふかい} : 深さ{ふかさ}...), while 速度{そくど} is the combination of two kanjis : 速{そく} (speed), 度{ど}(degree).
Can I guess anything based on the words etymology, or is the nuance between them is more subtle ?