One of the major differences between our common Physics models of energy change and realistic models of them is:

a
In the Physics models, the acceleration due to gravity is rounded to a non-exact but easier to use number
b
In the Physics models, the velocities are only calculated at set intervals of time, instead of continuously
c
In the Physics models, the objects are assumed to have simplified shapes in order to make motion by acceleration easier to calculate
d
In the Physics models, we do not take into account the energy change by the friction of moving components