Thermal energy is disordered energy. The individual atoms and molecules that make up an object have potential and kinetic energy, but they move in a random fashion about their equilibrium position in the object, so that the object as a whole remains at rest. The more kinetic energy is stored in the random motion of the atoms or molecules, the higher is the temperature of the object. Macroscopically, forces that do work converting ordered energy into disordered energy are non-conservative forces . P 1 to position P 2 depends on the path of the object.
Friction is an example of such a non-conservative force.
The work done by the force of friction converts ordered energy into thermal energy. When a system is acted on by an external force, then energy can be transferred into or out of the system. An external force can do work against internal forces and change the potential energy of the system or it can be a net force changing the kinetic energy of the system. A 70kg diver steps off a 10m tower and drops straight down into the water. If he comes to rest 5m below the surface of the water, determine the average resistance force exerted on the diver by the water.