Whenever a helicopter has two sets of lifting blades, they rotate in opposite directions (and there will be no tail propeller.) explain why it is best to have the plates rotate in opposite directionsPlease answer/explain

17 . Whenever a helicopter has two sets of lifting blades, they rotate in opposite directions (and there will be no tail propeller). Explain why it is best to have the blades rotate in opposite directions. 18 . Describe how work is done by a skater pulling in her arms during a spin. In particular, identify the force she