We can measure the vertical force by using hanging scales based on lever principle.Torsion balance can be freely twisted around wire and the torque(τband)is equal to the torsion constant for the band(κ)times the angle through which it is twisted(θ),or τband = –κθ,so it can measure the horizontal force.Combining with their characteristics,we can design a new kind of balance which can measure the size of ampere force on metal bar.