How i can force a person who is capable but not willing to perform his job?

You don't have to force someone to do his job, Just try to encourage him.

CAN YOU FORCE AN ADDICT INTO REHAB ?

Work motivation "is a set of energetic forces that originate both within as well as beyond an individual's being, to initiate work-related behavior, and to determine its form, direction, intensity, and duration"

Understanding what motivates an organization's employees is central to the study of I–O psychology. Motivation is a person's internal disposition to be concerned with and approach positive incentives and avoid negative incentives. To further this, an incentive is the anticipated reward or aversive event available in the environment.

While motivation can often be used as a tool to help predict behavior, it varies greatly among individuals and must often be combined with ability and environmental factors to actually influence behavior and performance.

Results from a recent2012 study, which examined age-related differences in work motivation, suggest a “shift in people's motives” rather than a general decline in motivation with age. That is, it seemed that older employees were less motivated by extrinsically related features of a job, but more by intrinsically rewarding job features