2. Work done by a variable force(变力的功) F is a variable force(3])acting on a particle moving along a curvilinear(曲线) path. Let us find the work done(作功) by it as follows:2. Work done by a variable force（变力的功） is a variable force (变力) acting on a particle moving along a curvilinear（曲线） path. Let us find the work done （作功）by it as follows ： F  i r   Fi   i