1. Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad
ENGINEERS MECHANICS
STATICS
CHAPTER 5
Lecture Notes:
Professor A. Salam Al-Ammri
Suhad Ibraheem Mohammed
Al-Khwarizmi College of Engineering
University of Baghdad
Analysis of Structures Trusses
Machines
2/17/2012
Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad

2. Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad
Contents
Introduction
Machines
Sample Problem 5.6.1
Sample Problem 5.6.2
Sample Problem
Sample Problem 5.6.4
Sample Problem 5.6.5
2/17/2012
Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad

3. Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad
Machines
Machines are structures contain moving parts whose components are capable of relative motion when not attached to a support, designed to transmit and modify forces. Their main purpose is to transform input forces into output forces.
2/17/2012
Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad

4. Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad
Sample Problem 5.6.1
To determine the center of gravity of a non-uniform bar that weights 24 N, an engineer suspends the bar from a wire at point A and supports it at point B on a knife edge that rests on a pan of a balance. A weight of 16 N is required to balance the bar in a horizontal position. Determine the horizontal distance d from point A to the center of gravity of the bar.
draw a free-body diagram of the scale
draw a free-body diagram of the bar.
2/17/2012
Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad

5. Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad
Sample Problem 5.6.2
A tackle on the football team weighs 350 lb. In coming off his stance, he places his entire weight on the ball of his foot. In effect, his foot acts as a lever. The weight of the tackle is transmitted to his foot through the tibia. In tern the Achilles tendon pulls on the heal consider the static effects only, determine the force that the tendon must withstand.
2/17/2012
Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad

6. Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad
Sample Problem 5.6.3
What forces are exerted on the bolt at E in Fig. as a result of the 150-Nforces on the pliers?
α= tan -1(30/70) = 23.2°
ΣFx= 0 , Dx+ Rcos α= 0
ΣF y= 0, D y − R sin α+ 150 = 0
ΣMB= (30)D y −(100)(150) = 0
D x= −1517 N , D y= 500N
R= 1650N
ΣMC= −(30)E−(30)D x= 0
E = −D x= 1517 N
2/17/2012
Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad

7. Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad
Sample Problem 5.6.4
In using the bolt cutter, a worker applies two 100-lb forces to the handles. Determine the magnitude of the forces exerted by the cutters at the bolt.
Explode the head off of the shears:
2/17/2012
Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad

8. Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad
Sample Problem 5.6.5
The bucket of the backhoe and its contents have a weight of 1200 lb and a center of gravity at G. Determine the forces of the hydraulic cylinder AB and in links AC and AD in order to hold the load in the position shown. The bucket is pinned at E.
2/17/2012
Professor Dr. A.Salam Al-Ammri & Suhad Ibraheem Mohammad