But systems can lose energy, like when friction from the box dragging on the floor generates heat.
但是系统可能会断电，例如 当盒子与地面摩擦时，它会产生热量。
英语百科
Skin friction drag
Skin friction drag is a component of parasitic drag that occurs differently depending on the type of flow over the lifting body (laminar or turbulent). Just like any other form of drag, the coefficient of skin friction drag is calculated with various equations and measurements depending on the flow and then added to coefficients of other forms of drag to calculate total drag.