Lab 10: Static Equilibrium
Name: __________________________
Goals:
- Analyze the forces and torques acting within a variety of static systems.
Solving Statics Problems:
To solve a statics problem, we simply apply the two conditions of equilibrium:
F  0
and
  0 .
There are a couple
noteworthy points about the process:
- If the net force vanishes, then the net horizontal and net vertical forces vanish separately:
F
x
 0 and  Fy  0 .
- To compute the net torque in terms of all the unknowns of the problem, you must choose a rotation axis. In many
cases, you can choose the rotation axis wisely in order to eliminate a variable – if we don’t care about an
unknown force on a hinge, for example, we can put our rotation axis at that hinge (this makes the torque exerted
by the hinge equal to zero, since the lever arm is zero).
- The torque exerted by gravity on a rigid body is computed as if the weight acts on the center of mass of the object.
A weight supported by strings.
Build the system shown below at your station (use C-clamps to stabilize the vertical rods). The 1.0 m horizontal distance is measured
at the points where the string loses contact with each pulley.
1.0 m
T2
T1
50cm
80cm
m  500g
1. Compute q1 and q2 . The “law of cosines” provides the easiest method.
q1 = _____
q2 = _____
2. Compute the tension in each string. Make your work very clear.
T1theoretical  ________
T2theoretical  ________
3. Insert a spring scale into the vertical section of each string in order to measure each tension.
T1measured  ________
T2measured  ________
% difference = ________
% difference = ________
Balanced meter stick #1
1. Attach a 1 kg mass to one end of the aluminum meter stick as shown.
10 cm
x
1000 g
2. Calculate the position (x) at which the meter stick will balance on a fulcrum. Also compute the upward force F exerted by the
fulcrum.
xtheoretical  ________
Ftheoretical  ________
3. Use a loop of string as your fulcrum and hang the system from a spring scale. Measure the actual balance point and the actual
upward force exerted at the balance point.
xmeasured  ________
Fmeasured  ________
% difference = ________
% difference = ________
Balanced meter stick #2
1. Build the system shown below. The pivot is a small nail inserted through the 10 cm. mark of the meter stick.
T
10 cm
30 cm
40 cm
10 cm 10 cm
pivot
m  500 g
m  200 g
2. Calculate the tension, T in the string. Make your work very clear.
Ttheoretical  __________
3. Insert a spring scale into the vertical part of the string in order to measure T :
Tmeasured  __________
% difference = ______
Balanced meter stick #3
1. Build the system shown below:
T
30 cm
10 cm
60 cm
20 cm
10 cm
pivot
m  200 g
2. Calculate the tension, T in the string.
Ttheoretical  __________
3. Insert a spring scale into the vertical part of the string in order to measure T :
Tmeasured  __________
% difference = ______