PHYS 1411: Introductory Physics Lab
Lab Instructor: Nouf Al-Jalaud
FORCES AT EQUILIBRIUM
Student Name: Fatma AL-Naimi
ID: 200700175
Section: 211
Submission date: 12/10/2012
1-Abstract (OBJECTIVE): To study an example of an object under static equilibrium and to
find its unknown mass.
2-THEORY:
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.
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. Method:
1) Stick on a fixed M3 at the angle of 270o on the force table.
2) Now, 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, ө1 and ө2.
5) Find the respective weights of M1, M2 and the unknown M3 as F1, F2 and W. Clearly,
the two forces F1and F2 are balanced by the force W.
6) Repeat step (1) at least four times for different angles.
4- Data:
Force F1 = M1g =__________ (N)
Force F2 = M2g =__________(N)
Trials M1 ө1
sin ө1 M1sin ө1 M2 ө2
1.
2.
3.
4.
0.6
0.54
0.54
-5.57
50
25
25
40
39
33
33
352
30
13.6
13.5
4
40
20
25
50
sin ө2 M2sin ө2 M3(g)
(=W/g)
189 0.20 8
25.21
150 0.5
1
23.6
151 0.48 10
25.7
43 0.68 30
28.53
The Average Value (AV) of the Unknown Mass = ____________ g
The Standard Deviation (SD) =_____________ g
The Percentage Error = (SD/AV) ×100% = ___________%
5. Data Analysis (Results Discussion)
(Fig.1)
If we are given two known weights, M1 and M2 ,(Fig.1), inclined at angles ө1 and ө2
respectively with the X-axis (in this case), then using first condition of equilibrium, we
can find the unknown weight, W :
∑Fy = 0
M1sinө1 + M2 sinө2 – W = 0
6. Conclusion
When all the forces that act upon an object are balanced, then the object is said to be in a state of
equilibrium. To improve the experiment M3 should be constant to give us food result.