Home / Topics / Work, Energy & Power
Non-conservative forces
Intermediate
Friction and drag dissipate mechanical energy.
Friction, drag and many human forces do path-dependent work and convert mechanical energy to heat. Total energy is still conserved but mechanical energy isn't.
A block sliding 3 m with 5 N friction loses 15 J to heat.
Don't assign potential energy to friction.
In more detail
A non-conservative force, such as friction or air resistance, does work that depends on the path. Its work removes mechanical energy from the system, usually converting it to thermal energy.
Real-world uses
- Brakes convert kinetic energy into heat through friction.
- Air resistance slows falling objects and reduces the energy available for motion.
- Brakes, air drag and friction in a machine convert mechanical energy into heat, so the energy is no longer available as motion.
Open the interactive lesson, with simulation and quiz →
Frequently asked questions
Where does the energy go?
Mostly into heat and sound, which spread into the surroundings.
Can non-conservative forces ever add energy?
Yes, a motor or engine can supply work, but it is a non-conservative force from the system's viewpoint.
Does non-conservative work destroy energy?
No. It converts mechanical energy into thermal or other forms, and the total energy is still conserved.
Related topics in Work, Energy & Power
Gravitational potential energy · Elastic potential energy · Conservative forces · Force from potential energy · Potential energy curves · Equilibrium types