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,vanda.
For sake of completeness these should be written as s,vanda.

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

For any vector X, component in the direction which makes an angle θ with the vector is given by Xcosθ.
It follows that for θ=90, (i.e., in the perpendicular direction)
cos90=0
Xcos90=0

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