1 The moment (turning effect) of a force depends on two factors. What are they? 2 What is the principle of moments? What other rule also applies if an object is in equilibrium? 3 Below, someone is trying to balance a plank with stones. The plank has negligible weight. a Calculate the moment of the 4 N force about O. b Calculate the moment of the 6 N force about O. 2 m -2 m- 4 m. 4N 6N Will the plank balance? If not, which way will it tip? 4 d What extra force is needed at point P to balance the plank? e In which direction must the force at P act? In diagram B on the opposite page: a What is the upward force from the support? b If moments are taken about point P, which forces have clockwise moments? What is the total clockwise moment about P? c Which force or forces have anticlockwise moments about P? What is the total anticlockwise moment about P? d Comparing moments about P, does the principle of moments apply?