Figure 13-44 gives the po- tential energy function U(r) of a projectile, plotted outward
from the surface of a planet of radius Rs. What least kinetic energy is required of a projectile launched at the surface if the
projectile is to “escape” the planet?

If there was no gravity then their would be no downword force on the football to have it return the the grownd, and if there was no friction (mainly air friction) then there would be no opposing force the stop the ball from moving through the air allowing the ball to travle ∞.

The objects do not reach terminal velocity         there is not enough time from the time the object falls from when it hits the ground to achieve terminal velocity. an object must be placed higher to achieve terminal velocity in order to be in free fall.