Scientists have studied the aerodynamic forces generated by a flying insect by tethering it to the center of a taut, horizontal wire. as the insect "flies" in a wind tunnel, the insect exerts forces on the wire that a researcher can detect by measuring the wire’s deflection. to calibrate the wire, a known force must be applied to it. this is done by passing a current through the wire while it is positioned in a magnetic field that is perpendicular to the wire. the researcher requires the force on the wire to point upward with a magnitude of 4.2x10-4 n.