Now consider particle P that moves from point A to point B again, but this time it moves along the nearby trajectory that differs from r (t) by the variation δ r (t) = ε h (t), where ε is a scaling constant that can be made as small as desired and h (t) is an arbitrary function that satisfies h (t 0) = h (t 1) = 0. Suppose the force F (r (t) + ε h (t)) is the same as F (r (t)). The work done by the force is given by the integral W ¯ ¯ = ∫ ∫ r ( t 0 ) = A r ( t 1 ) = B F ⋅ ⋅ d ( r + ϵ ϵ h ) = ∫ ∫ t 0 t 1 F ⋅ ⋅ d ( r ( t ) + ϵ ϵ h ( t ) ) d t d t = ∫ ∫ t 0 t 1 F ⋅ ⋅ ( v + ϵ ϵ h ˙ ˙ ) d t . The variation of the work δW associated with this nearby path, known as the virtual work, can be computed to be δ δ W = W ¯ ¯ − − W = ∫ ∫ t 0 t 1 ( F ⋅ ⋅ ϵ ϵ h ˙ ˙ ) d t .