Compressed spring. Image 2 of 3. This spring is being used for a demonstration of Hooke's Law. Hooke's Law states that, up to an elastic limit, the compression or extension of a spring is proportional to the force applied. So, when weights are added to this spring, the measured compression correlates linearly with the weight applied. To see the apparatus before the addition of weights and after the addition of more weights, see images A400/109 and A400/111.