1. Starter If the stick is balanced, how are the masses and distances related? m 1 r 1 + m 3 r 3 = m 2 r 2 + m 4 r 4

2. Practice – Torque Problem Set  = rF  For the stick;  = mgr  ( units = N. m )

3. Example m 1 = 50grams, r 1 = 30cm, and r 2 = 20cm. 1.Find m 2. 2.Find the clockwise torque. 3.Find the counter-clockwise torque. 1. m 1 r 1 = m 2 r 2 so m 2 = m 1 r 1 / r 2 = 50(30)/20 = 75 grams. 2.  = rF = m 2 gr 2 = (.075kg)(9.8 m/s 2 )(.20m) =.147 Nm 3. If balanced, counter-clockwise torque = the clockwise torque =.147Nm

4. Exit To turn a stubborn screw, is it easier to use a screwdriver with a wide handle of a narrow handle? Explain.