Experiment 8
FIRST CONDITION OF EQUILIBRIUM USING TENSION PROTRACTORS
OBJECTIVE
To verify the first condition of equilibrium.
MATERIALS
2-Tension Protractors, 2-large Table Clamps, 3-90 cm Steel Rods, 2-Multi
Clamps, Hooked mass set, Strings and Balance
THEORY
The first condition by which an object remains at equilibrium (either at rest, or in
straight – line motion with constant speed) states that the net external force acting
on the object must be zero. Any object hangs at rest if its weight is counteracted by
other forces, so that the vector sum of all concurrent forces along the vertical and
the horizontal directions is zero. In this activity, the weights hanging on the left,
right, and center objects are considered as tensions on the left, right, and center
cords, respectively. If the system remains at rest, then the sum of the upward
components of the tensions in the left and right cords is equal in magnitude to the
weight of the center object. Likewise, the leftward component of the tension in the
left cord is equal in magnitude to the rightward component of the tension in the
right cord.
ΣF N = 0
For Components: ΣF X = 0 , ΣF y = 0, and ΣF Z = 0
PROCEDURE
1. Clamp two rods (90 cm long) vertically to the table, approximately 80 cm
apart. Attach two Tension Protractors (oriented with zero degrees
horizontal) to a cross rod, and clamp this rod between the vertical rods as
shown in the Figure 8 (but don’t attach the mass yet).
Figure 8
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2. Zero the force scale of each Tension Protractor: Without anything attached to
the Tension Protractor string, adjust the thumb screw in the back until the
force scale reads zero.
3. Zero the angle scale of each Tension protractor. Hang a small mass (10 g)
from the hook. Rotate the outer ring to align the 90o mark with the string.
4. Cut a string about 60 cm long. Tie a loop about 25 cm from one ends so that
the string length on one side of the loop is about 20 cm and the string length
on the other side of the loop is 35 cm. Tie one end of the string to the wire
hook on one of the Tension Protractors and tie the other end of the string to
the wire hook of the other Tension Protractor. Hang a 200 g mass from the
string loop.
5. Read the magnitude of force and the angle measured from the +x-axis
counter clockwise for each string and record them in Table A.
6. Record the hooked mass and use a balance to find its exact mass. Record it in
Table A.
7. With a convenient scale of unit length for every unit force, construct
graphically (polygon method) the vector sum of the left, right, and center
cords.
ANALYSIS
1. Calculate the weight of a hanging mass and record it in table B.
2. Calculate the x-and y- components of the tension of each string. Record them
in Table B.
3. Complete the table B, showing all your computations in its completion.
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Name:
Date:
Course, Year, & Section:
Group No. :
Experiment 8
FIRST CONDITION OF EQUILIBRIUM USING TENSION PROTRACTORS
Table A
Magnitude of Force
(N)
CORD
Angle in degrees measured
from the +x-axis
counterclockwise
LEFT CORD (L)
RIGHT CORD (R)
CENTER CORD (C)
Graphical construction of vectors:
Table B
Cord
Left
Right
Center
Tension in Newton
Angle with
respect to
+x – axis
Components of Forces Along
x – axis
270o
Total
Resultant
y – axis
0
R =
θR =
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CALCULATIONS
QUESTIONS
1. In Step 2 of method A, why should the center weight be less than the sum of
the left and right weights?
Skip this question.
2. The net external force acting on an object is zero. Is it possible for the object
to be traveling with a velocity that is not zero? Justify your answer.
3. The steel I beam in the drawing has a weight of 8.00 kN and
is being lifted at constant velocity. What is the tension in
each cable attached to its ends?
o
70
o
70
4. In the figure below, find T 1 and T 2.
5m
θ2
θ1
4m
T2
T1
3m
500 N
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