The left main landing gear of the single-engine airplane collided with an unmarked guide wire during a simulated forced landing. The 6,130-hour flight instructor reported that while on the crosswind leg of the traffic pattern, while at about 600 feet above ground level (agl), he applied engine carburetor heat, reduced the engine power to idle, and asked the 156-hour student pilot to perform a simulated emergency power off forced landing. As the two-seat single-engine airplane was descending, the flight instructor asked for the flight controls in order to "demonstrate a secondary field for landing" to the pilot receiving instruction. During the demonstration, the airplane's left main landing gear contacted an unmarked static transmission wire which resulted in a loss of control and an uncontrolled descent to the ground. The airplane impacted the ground with the outboard section of the right wing and came to rest in an inverted position. There was no postimpact fire and both occupants were able to exit the airplane unassisted. The flight instructor reported that there was no mechanical malfunction or failure with the airplane prior to the accident.