At the surface of the Earth, the acceleration of all objects due to gravity
is about 9.8 m/s².
So an object that's acted on by no other forces except gravity increases
its speed by 9.8 m/s every second.
If the object is dropped from "rest" (zero speed), then after 1.5 seconds
have passed, it's falling at (1.5 x 9.8) = 14.7 m/s .
Its velocity is 14.7 m/s in the direction of straight down.
