energy dissipation
Summary
Energy dissipation is the conversion of organized energy, such as mechanical or electrical energy, into thermal energy that spreads out and is hard to recover. Total energy is still conserved, but the mechanical energy of the system typically decreases.
Detail
Meaning: Energy dissipation is the conversion of organized energy, such as the kinetic or potential energy of a moving object, into thermal energy spread among random molecular motions. Nonconservative forces (kinetic friction, air drag, viscous drag) do this, and so does current through a resistor. The energy is not destroyed, but it is usually too spread out to be fully turned back into work.
Equation: Edissipated = −Wnc = (KEi + PEi) − (KEf + PEf), where Edissipated is energy converted to heat (J), Wnc is work by nonconservative forces (J), and KE and PE are kinetic and potential energy (J) at the initial (i) and final (f) points. For sliding friction, Edissipated = fk d, with fk in N and d in m.
On the MCAT: Typical setups are a block sliding down a rough incline, a ball bouncing to lower heights, or a pendulum whose swing shrinks. Heat produced equals initial minus final mechanical energy. In circuits, a resistor dissipates power P = I²R (W), with I in A and R in Ω. In fluids, viscosity dissipates energy, so pressure falls along a pipe.
Common confusion: Dissipation does not violate conservation of energy. Total energy is conserved; only mechanical energy is lost. Static friction with no slipping, as in rolling without slipping, typically dissipates little or no energy.
Sources
- Physics (Giancoli)
- Fundamentals of Physics (Halliday, Resnick, Walker)
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.