The unit tangent vector T(t) of a vector function is the vector that’s 1 unit long and tangent to the vector function at the point t. Remember that |r'(t)| is the magnitude of the derivative of the vector function at time t. The unit normal vector N(t) of the same vector function is the vector that’s 1 unit long and perpendicular to the unit tangent vector at the same point t.

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