Conservation of mechanical energy states that the mechanical energy of an isolated system remains constant without friction.
According to Work – Kinetic Energy theorem:
Wnet = ΔKE where Wnet is the net work in a system and delta KE is the change in kinetic energy.
If only conservative forces act, then Wnet=Wc, where Wc is the total work done by all conservative forces. Thus, Wc = ΔKE. Now, if the conservative force, such as the gravitational force or a spring force, does work, the system loses potential energy (PE). That is, Wc = −PE. Therefore,
−ΔPE = ΔKE
This equation means that the total kinetic and potential energy is constant for any process involving only conservative forces. That is,
KE + PE = constant
In any real situation, frictional forces and other non-conservative forces are always present, but in many cases, their effects on the system are so small that the principle of conservation of mechanical energy can be used as a fair approximation. Though energy cannot be created nor destroyed in an isolated system, it can be internally converted to any other form of energy.
MCAT Official Prep (AAMC)
Physics Online Flashcards Question 14
• The conservation of mechanical energy can be written as “KE + PE = const”.
• Though energy cannot be created nor destroyed in an isolated system, it can be internally converted to any other form of energy.
Conservation: a particular measurable property of an isolated physical system does not change as the system evolves.
Frictional force: frictional force is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other.
Isolated system: a system that does not interact with its surroundings, that is, its total energy and mass stay constant
Kinetic energy: kinetic energy of an object is the energy that it possesses due to its motion
Conservative force: a force with the property that the total work is done in moving a particle between two points is independent of the taken path