# Sense of Coriolis force and Tractive force

I was solving a problem in Mechanics of material point and a part required to calculate the coriolis and tractive forces. So in the solution of this problem I realized that my answer missed the fact that the coriolis force is opposite in direction to coriolis acceleration and that the tractive force is opposite to the tractive acceleration. Why are they opposite to their corresponding accelerations? Aren't they supposed to have exactly the same direction as their corresponding accelerations according to Newton's second law? Any help is appreciated.

Suppose that you are observing in a inertial frame a mass $$m$$ acting on by a force $$\vec F$$ accelerating with an acceleration $$\vec a$$. $$\vec F = m\,\vec a$$
If you jump into the frame of the mass (ie a frame moving with the mass) then you observe that the mass is not acceleration in that frame and yet the mass has a force $$F$$ acting on it.
To enable you to use Newton's laws in the frame which is moving with the mass you add an extra (pseudo) force $$m \,(-\vec a)$$ so that the net force on the mass in this frame is $$\vec F + m \,(-\vec a) =m\,\vec a + m \,(-\vec a)= 0$$.