1. Centroid: According to the American Heritage Dictionary, "centroid" is synonymous with "center of mass" or CM. When I was in high school, we called that MARKAZ AL-THIQAL مركز الثِقَل

Al-Khatib's New Dictionary of Scientific and Technical Terms prefers MARKAZ MUTAWASSIT مركز متوسـط

If had my druthers, I would call it MARKAZ AL-KUTLA مركز الكُتلة.

2. Vector: When I was in high school, we called that MUTTAJIHA or KAMMIYYA MUTTAJIHA مُتَّجِهة أو كَـمِّـيّة مُـتَّجِهة

The above mentioned reference still uses the same term. A vector is a quantity that has both a magnitude and a direction. Mechanical forces, for instance, are vectors. A quantity that has a magnitude but no direction is called "scalar"

كمية سُـلَّميّة أو كمية لا متجهة أو غير متجهة
Volume, for instance, is a scalar.

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