{"data":{"fields":"term_definition","term_definition":"<div class=\"definition\">The pitch surfaces of gears are the imaginary surfaces which roll together without sliding. However, in order to transmit positive motion, the gears must have teeth which normally extend in both directions above and below the imaginary pitch surface. Since contact begins at some point away from the pitch surface and normally proceeds to the top of the driving tooth, only at the pitch surface is there pure rolling contact on gear teeth. At all other positions along the tooth profile, there is profile sliding. The amount of profile sliding is dependent on the distance from the pitch point and the relative velocities of the two gears. For parallel axes gears the formula for profile sliding at a point A distance S from the pitch point would be: Rs = 2 S (Np \u2013 Ng) Where Rs = sliding velocity, inch per min. S = distance from pitch point inch Np = pinion speed RPM Ng = gear speed RPM<\/div>"}}