Body:getLinearDamping
Gets the linear damping of the Body.

The linear damping is the ''rate of decrease of the linear velocity over time''. A moving body with no damping and no external forces will continue moving indefinitely, as is the case in space. A moving body with damping will gradually stop moving.

Damping is not the same as friction - they can be modelled together.
damping = Body:getLinearDamping()
damping number The value of the linear damping.