Experiment Name:
Force at Equilibrium
Student Name: Reem N. Al-Hajri
ID#201102217
Group members:
Noura Al-Moajil – Hala Al-Sulaiman – Mizna Alzamil
Section: 211
Submission date: 10/2/2012
PHYS 1411: Introductory Physics Lab
Lab Instructor: Nouf Al-Jalaud
Prince Mohammad Bin Fahd University
Fall 2012-2013
1. Abstract (Objective) 0.5 point
To study an example of an object under static equilibrium and to find it
unknown mass.
2. Theory 0.5 point
1. A vector quantity has both magnitude and direction. Weight,
displacement, velocity and force are vector quantities. We have to
consider the directions while adding vectors.
2. The first condition of equilibrium says that if an object is in translational
equilibrium, the net force acting on it must be zero.
Mathematically,
∑
𝐅𝐱 = 𝟎, ∑
𝐅𝐲 = 𝟎,
𝐀𝐧𝐝 ∑
𝐅𝐳 = 𝟎
3. If we are given two known weights, F1 and F2, inclined at angles 𝜃1
and 𝜃 2 respectively, then using first condition of equilibrium, we can
find the unknown weight, W:
∑
𝐅𝐲 = 𝟎
F1𝐬𝐢𝐧 𝜽 𝟏 + 𝑭𝟐 𝐬𝐢𝐧 𝜽𝟐 − 𝑾 = 𝟎
W=MG
3. Method 0.5 point
1. Find the equilibrium of the system by positioning the knot of thread
over the hole in the middle of the center post of the Force Table without
using the slotted masses. Pull the knot slightly to one side and let it go.
Check to see if the knot returns to the center. If not, then keep
adjusting till it does.
2. Hang the known slotted masses M1 and M2 onto the hangers on the
pulleys.
3. Fix the positions of the two masses and start adding masses to the
third pulley (M3) and adjust the angle till you reach the equilibrium.
4. Take the readings of the angles, 𝜃1 and 𝜃2.
5. Find the respective weights of M1, M2 and the unknown M3 as F1, F2,
and W. Clearly; the two forces F1 and F2 are balanced by the force W.
6. Repeat step (1) at least 3 times for different angles.
 APPARATUS REQUIRED:
1- Force Table Assembly
2- Three super pulley clamps
3- Three mass hangers
4- spool of thread
5- Slotted masses
2
4. Data 0.5 point
M3= 35 = at 270°
Trials
1
2
3
4
M1
60
50
40
20
θ1
18°
5°
-18°
-3°
sinθ1
0.31
0.09
-0.3
-0.05
M1sinθ1
18.54
4.35
-12.36
-1.05
M2
60
60
60
40
θ2
162°
146°
128°
122°
sinθ2
0.31
0.56
0.84
0.85
M2sinθ2
18.54
33.6
50.9
34
M3
37.08
37.9
38.5
33
5. Data Analysis (Results Discussion) 1 point
-First of all, we were changing the forces of M1 and M2 and change there
angles to reach equilibrium four times then we record them in the table as
shown before separately and find out the sin for the tow forces angles and
multiply it by there masses M1sinθ1, M2sinθ2 , then we will find M3 by
adding these tow results M1sinθ1+ M2sinθ2= M3.
-Secondly, we calculate the average value (M3 1 + M3 2 + M3 3 + M34) \ 4
-Finally, we find out our Percentage Error by this rule {(Approximate ValueExact Value) \ |Exact Value} x 100.
1) The average Value (AV) of the unknown Mass (M3) :
= (37.08 + 37.9 + 38.5 + 33 )/ 4
= 36.62 g
2) The percentage error:
= (36.62 – 35\ 35) x 100
= 4.62 %
6. Conclusion 0.5 point
Force at equilibrium experiment helped me to know how to balance forces by
specific procedures, and witch mathematical rules we should use to identify
the purpose of this experiment. Also, we have to be sure about recording the
right data to get the results that we wish for with a well experiment.
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