1. Equilibrium: the state of no acceleration– balanced forces and balanced torques
First condition of equilibrium: Fnet = 0
Second condition of equilibrium: τnet = 0
Static Equilibrium: Forces and Torques balance and the object is at rest
Center of Mass (cm)– the point around which gravitational torques balance– it is where the Fw can be considered to be “located” at C
For a uniform object, the cm is at the center: Fw

2. Solving Statics Problems
1) Forces are balanced horizontally and vertically
2) Torques are balanced as counterclockwise (+) and clockwise (-) around an arbitrarily placed pivot point F3 F1 CC PP C F2 C

3. CC F3 CC F1 F2 PP C F3 F1 C PP C CC F2

4. A uniform meterstick with a weight of. 150 N is balanced at the 75
A uniform meterstick with a weight of .150 N is balanced at the 75.0 cm mark by a mass hung at cm mark. How much is the mass that is producing equilibrium? How much does the stand push up? Ø Fs PP
.750 m C
.500 m
.400 m Fh C Fw CC

5. Tc = Tcc
Fw = .150 N
(Fh)(.150 m) = (.150 N)(.250 m)
mh = ?
Fh = (.150 N)(.250 m)
.150 m
= .250 N
m = Fh g
= .250 N
9.80 m/s2
= kg
Fdown = .150 N N
Fup = Fdown
= .400 N

6. A large wooden beam weighs 820 N and is 3. 2 m long
A large wooden beam weighs 820 N and is 3.2 m long. The beam’s center of gravity is 1.4 m from one end. Two workers begin carrying the beam away. If they lift the beam at its ends, how much weight must each worker support?

7. Ø Fu
Fu 2 CC PP
1.4 m
1.8 m
Fw = 820 N C

8. Tc = T cc
(820 N)(1.4 m) = (Fu2)(3.2 m)
Fu2 = (820 N)(1.4 m)
3.2 m
= 360 N
Fup = Fdown
Fu + Fu2 = 820 N
Fu = 820 N N = 460 N

9. 1) A 10.0 N meterstick is suspended from two spring scales, one at the 8.00 cm mark and the other at the 90.0 cm mark. If a weight of 5.00 N is hung at the 20.0 cm mark and a weight of 17.0 N is hung at the 55.0 cm mark, what will each scale read?
2) An 850 N painter stands 1.20 m from one end of a 3.00 m scaffold plank supported at each end by a stepladder. The scaffold plank weighs 250 N and there is a 50.0 N paint bucket .50 m from the other end of the plank. How much upward force is exerted by each of the two ladders?

10. 3) A 650. 0 N boy and a 490. 0 N girl sit on a 150
3) A N boy and a N girl sit on a N porch swing that is 1.70m and supported at each end by chains. What will be the tension in each chain if the boy sits .750 m from one end and the girl sits .500 m from the other end?
4) A uniform 2.50 N meterstick is hung from the ceiling by a single rope. A g mass is hung at the 25.0 cm mark and a g mass at the 70.0 cm mark. What is the tension in the rope and at what mark is the rope located on the meterstick?

11. 5) A 125 N uniform wooden plank is 2. 00 m long
5) A 125 N uniform wooden plank is 2.00 m long. It is supported by two sawhorses each placed .500 m in from each end. A man weighing 855 N stands m in from the left end. A bag of tools weighing 55.0 N is .250 m in from the right end. How much must each sawhorse push upward?
6) A 4.0 N meterstick is balanced at the 73.0 cm mark when a weight is hung from the 92.0 cm mark. How much weight is hanging from that mark? How much does the stand push upward?