There are two types of forces – conservative and non-conservative forces. If the work done by or against the force of moving the body depends only on the initial and final positions of the body and not on the nature of the path drawn between the initial and final positions, the force is said to be conservative.

Forces that don’t conserve energy are named non-conservative or dissipative forces. Friction is one of the non-conservative forces.

What are non-conservative forces? 

A non-conservative force is the one that depends on the path that work follows. It is path-dependent; therefore, it depends on the initial and final velocity. There is no potential energy associated with non-conservative forces. Non-conservative forces that do not store energy.

In simple terms, non-conservative forces can be defined as forces whose work depends on the path they follow. For example, if you drag something across a field of sandpaper, the friction force will do a different amount of work depending on the path. A double-length pass requires twice as much work to overcome friction.

Friction and non-conservative force 

• Force is either conservative or non-conservative. Non-conservative forces are forces that depend on the path the work takes 
• The work done on friction depends on the length of the path between the start and endpoints. Due to this path dependence, there is no potential energy associated with non-conservative forces 
• Work done by non-conservative is irreversible
• An important function is that work done by non-conservative forces adds or removes mechanical energy from the system 
• In any closed path, the total work done by a non-conservative force is not zero
• For example, friction produces thermal energy that dissipates and extracts energy from the system. Moreover, retaining or capturing thermal energy cannot be completely returned to work and cannot be lost or recovered in this sense either

Mechanical force and non-conservative force 

• All systems lose mechanical energy over time, contributing to the second law of thermodynamics
• It is important to note that non-conservative force does not destroy energy but only transforms it into a less useful (disordered) form 
• Friction forces such as air resistance are non-conservative forces. The energy it extracts from the system becomes unavailable to the system
• What is not conserved around the frictional distance is all potential energy and kinetic energy, forming mechanical energy
• In the case of friction, the loss of mechanical energy is converted into thermal energy. Including this thermal energy, it can be said that the total amount of energy does not change. However, the heat energy is immediately released into the environment

Properties 

The properties of a non-conservative force is as follows: 

• Energy is dissipated as heat energy
• The work done is not entirely recoverable 
• In any closed path, the total work done by a non-conservative force is not zero
• There is no potential energy function of frictional force.
• The work done by non-conservative is irreversible
• When a force causes a change in mechanical energy, that force is called a non-conservative force. This is nothing but the sum of potential energy and kinetic energy
• Work done by non-conservative forces adds or removes mechanical energy

Conclusion

If both conservative and non-conservative forces are working, instead of finding net work done from net force or from, applying energy conservation and exercise in terms of known potential energy with conservative force is used to calculate the work done by non-conservative force.

Forces are said to be non-conservative as they are path-dependent. Therefore, it also depends on the initial and final velocity. This means that the value of the work done depends on the path. Friction is a non-conservative force because the work done on friction depends on the length of the path travelled by body movements.