Complex sentence: He quarrels with his friends when they start purchasing the machines and is only stopped from horsewhipping his own car-mad son, Bob (Charles Emmett Mack), by the timely appearance of Bob's girlfriend, Rose Robbins (Patsy Ruth Miller).
Split into simpler sentences: He quarrels with his friends when they start purchasing the machines. He is only stopped from horsewhipping his own enthusiastic son, Bob (Charles Emmett Mack), by the timely appearance of Bob's girlfriend, Rose Robbins (Patsy Ruth Miller).