1. 6 STATICS ENGINEERS MECHANICS CHAPTER Lecture Notes:
Professor A. Salam Al-Ammri
Suhad Ibraheem Mohammed
Al-Khwarizmi College of Engineering
University of Baghdad
Impending Tipping vs Sliding.
2/17/2012
Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad

2. 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

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

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

5. 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

6. 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 = 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

7. 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

8. 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

9. 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

10. 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.
N is less than N. So it will not tip.
2/17/2012
Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad