Moving Object Detection (MOD) is still an activearea of research due to the amount of scenarios it can tackleand the different characteristics that may appear in them.Therefore, getting a unique method that performs well in allthe situations becomes a challenging task. In this paper weaddress theMODproblem from a physical point of view: giventhe optical flow between two images, we propose to find itsmotion-boundaries by means of the optical strain, which givesinformation about the deformation of any vector field. As opticalstrain detects all the motions from a sequence, we propose towork on temporal windows and apply thresholding on them inorder to separate noise from real motion. The proposed approachshows competitive results when compared to other methods onknown datasets.