Work and Energy - Mission WE5 Detailed Help

Some forces are categorized as conservative forces (or internal forces) while others are categorized as non-conservative forces (or external forces). Which of the following forces are generally categorized as non-conservative (or external) forces?


 
Definition of Conservative Force:
All the different types of forces that could do work upon an object can be categorized as either conservative or non-conservative forces. A conservative force is a type of force that serves to transform an object's energy between kinetic and potential. When only conservative forces do net work upon an object, the energy of the object changes forms (KE to PE or vice versa) without changing the total amount of mechanical energy.


 
Definition of Non-conservative Force:
All the different types of forces that could do work upon an object can be categorized as either conservative or non-conservative forces. A non-conservative force is a type of force that changes the total amount of mechanical energy possessed by an object. When non-conservative forces do work upon an object, the total amount of mechanical energy changes.


 
There are two forces commonly discussed in MOP questions that serve as conservative forces - gravity and spring. All other forces are regarded as non-conservative forces. The force of gravity, when it does work, serves to change gravitational potential energy into kinetic energy or vice versa. The spring force, when it does work, serves to change elastic potential energy into kinetic energy or vice versa. Whenever forces other than gravity and spring forces do work upon an object, you can be certain that the total mechanical energy of that object will change.