Why are vertical and horizontal motion considered independent?

1 Answer
Nov 2, 2016

We know that in motion problems, displacement, velocity and acceleration all are vector quantities. Only for the sake of simplicity these are written as s,v and as,vanda.
For sake of completeness these should be written as vecs, vecv ands,vand veca.a.

We also know that for vector quantities, orthogonal component is always equal to zero as shown below.

For any vector vecXX, component in the direction which makes an angle thetaθ with the vector is given by vecX cos thetaXcosθ.
It follows that for theta=90^@θ=90, (i.e., in the perpendicular direction)
cos90^@=0cos90=0
=>vecX cos 90^@=0Xcos90=0

As such vertical and horizontal components of motion can be treated independently.