reaction; recoil; kick; backlash
motion
銃の反動で肩が痛い。
My shoulder hurts from the gun's recoil.
急な改革には必ず反動が伴うものだ。
Rapid reform is always accompanied by backlash.
ダイエットの反動で三日間食べ過ぎてしまった。
I overate for three days as a backlash from dieting.