Jerry's bag of marbles is twice as heavy as jim's. if it takes 5 extra marbles to make jim's bag feel heavier, it will take 10 extra marbles to make jerry's bag feel heavier. this best illustrates:

This best illustrates Weber's Law. This law is all about human perception and slight change. For Weber's Law to take effect something must be slightly changed from its original state to create a slight difference. This slight difference is proportional to the object's original state. Jerry's bag will feel heavy enough to make Jerry believe their is a slight difference from the bag initial state.