# When some mass does vertical upward motion, which direction is the direction of the inertial force?

When I throw a ball upward on the earth, at a later time, that ball would be in the condition of $$v=0$$ (at the highest position) and then finally it would fall. If a ball falls, its direction of inertial force is upward. However, from it's initial condition to the $$v=0$$ condition (the highest position), or when its velocity is upward, the direction of movement and the direction of acceleration is opposite. In this condition, what is the direction of inertial force?

• In what reference frame are you asking this? Note that there are no inertial forces in inertial reference frames. Mar 7, 2021 at 2:02

And we know that the object falling is in a uniform gravitational field that acts downwards and at the rate given by $$g$$ and the value of this force is $$mg$$ for a mass $$m$$.
"(Inertial mass) $$\cdot$$ (Acceleration) = (Intensity of the gravitational field) $$\cdot$$ (Gravitational mass)"