In the absence of other forces, gravity results in a constant downward acceleration of every freely moving object. Near Earth's surface the acceleration due to gravity is g = 9.8 m⋅s−2 and the gravitational force on an object of mass m is Fg = mg. It is convenient to imagine this gravitational force concentrated at the center of mass of the object.
If an object is displaced upwards or downwards a vertical distance y2 − y1, the work W done on the object by its weight mg is:
W = F g ( y 2 − y 1 ) = F g Δ y = − m g Δ y {\displaystyle W=F_{g}(y_{2}-y_{1})=F_{g}\Delta y=-mg\Delta y}
where Fg is weight (pounds in imperial units, and newtons in SI units), and Δy is the change in height y. Notice that the work done by gravity depends only on the vertical movement of the object. The presence of friction does not affect the work done on the object by its weight.