6 STATICS ENGINEERS MECHANICS CHAPTER Lecture Notes: Professor A. Salam Al-Ammri Suhad Ibraheem Mohammed Al-Khwarizmi College of Engineering University of Baghdad asalaam.kecbu@uobaghdad.edu.iq Impending Tipping vs Sliding. 2/17/2012 Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad

Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad Contents Introduction Impending Tipping vs Sliding. Sample Problem 6.2.1 Sample Problem 6.2.2 Sample Problem 6.2.3 2/17/2012 Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad

Impending Tipping vs Slipping 2/17/2012 Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad

Impending Tipping vs Slipping 2/17/2012 Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad

Impending Tipping vs Slipping Mo =0 :- Ph + Wx =0 , x = P.h/W Impending Motion (Fs = s N) If (x < l / 2) then block will slide. If (x = l / 2) then block is unstable. If (x > l / 2) then block will tip. In Motion (Fk = k N) Fs becomes Fk ,s > k , Fs > Fk 2/17/2012 Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad

Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad Sample Problem 6.2.1 The drum has a weight of 100 lb and rests on the floor for which the coefficient of static friction is ms = 0.5 . If a = 3ft and b = 4ft determine the smallest magnitude of the force P that will cause impending motion of the drum. 2/17/2012 Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad

Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad Sample Problem 6.2.2 If each box weighs 150 lb, determine the least horizontal force P that the man must exert on the top box in order to cause motion. The coefficient of static friction between the boxes is μs = 0.35 , and the coefficient of static friction between the box and the floor is μs = 0.65 Free Body Diagram:There are possible motion,namely(1)the top box slides,(2) both boxes slide together as a single unit on the ground,and (3) both boxes tip as a single unit a bout point B. Assume both boxes tip as a single unit about point B.Thus ,x=1.5 ft. 2/17/2012 Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad

Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad Sample Problem 6.2.2 Since F<Fmax =μsN=0.35(300)=105 lb ,both boxes will not slid as a single unit on the floor. Fig.b: Since F<Fmax =μs N=0.65(150)=97.5 lb , the top boxe will not slid Thus the assumption is correct. 2/17/2012 Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad

Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad Sample Problem 6.2.3 The mass of refrigerator is 110 kg. It is supported at A and B.The distance h =1520 mm and b = 360 mm. The coefficient of static friction at A and B is 0.2. What is the force F is necessary to impending slip? Will the refrigerator tip over before it slips? 2/17/2012 Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad

Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad Sample Problem 6.2.3 Check to see if the refrigerator will tip over, the forces at A would disappear and NB would hold the entire weight of the refrigerator. 215.82 N is less than 255.58 N. So it will not tip. 2/17/2012 Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad