Download 121 Lab 10 - Equilibrium Lab

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Physics 121: Lab 10 – Equilibrium
Introduction
In this lab, you will investigate the forces and torques on an object in equilibrium. You may want to reference the
following concepts from your course textbook and/or other resources:



Force
Torque
Equilibrium and/or statics
Remember to prepare yourself prior to completing the lab by reading documents regarding procedures and use of lab
equipment and by reviewing the above topics.
Equipment
In this lab you will use the following equipment: Cougar-shaped sign attached to a whiteboard with an adjustable
bearing pin, hanging masses, pulleys, string, a protractor, a level, a scale, and a ruler. Please be careful not to damage
the equipment by using it inappropriately. Please be careful not to damage the equipment by using it inappropriately.
Experiment/Analysis
Please read all instructions/procedures posted on the lab table and questions listed below before beginning the lab.
Then quickly complete your experiments and move to another table to discuss the questions.
Part I:
The cougar-shaped sign (see below) can be hung such that the arm which reads “COUGARS” is level. The bearing
pin only allows the left side of the sign to rotate when it is pushed in. (Note: When it is pulled out, the left side can
move up, down, left and right, and rotate.) The right side of the sign has a string (i.e. – the guy wire) looped over a
pulley that can support the sign when a mass is attached to the other end of the string. With the bearing pushed in,
adjust the angle of the string (between 30° and 70°) and the mass on the string until the sign is leveled. Label the figure
below with all of the forces on the sign. Be sure your drawing indicates the direction of the forces and includes
symbolically labeled angles, distances, and forces (e.g. – θstring, ⃗⃗⃗⃗⃗⃗⃗
𝐹𝐶𝑀 , etc.). Determine how far the center of mass of
the sign is from the bearing pin. Explain how you determined the distance and how it compares to the labeled mark
on the sign.
60 degrees and 600g and mass of sign 825
Tension=rFsintheta
r=(.6*9.8)sin(60)
Pin to mark=23 cm
Mark to edge=14 cm
Since the sign was at equilibrium we were able
to calculate the distance to the center of mass
using the tension force and the angle at which it
was applied.
For help on lab equipment issues, please email [email protected], call 801-422-5393, or come to room N490 ESC.
In case of life-threatening emergencies, immediately call 801-422-2222.
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Part II:
Use your measured values to determine the magnitude and direction of the force that the bearing pin exerts on the
sign. Note down each quantity that you either measured or calculated in the table below. Write down your calculations,
including an explanation for each step, in the space below.
Quantity
Value
500
40
420
45
600
20
Torque = .23(.5*9.8)sin(40)= Torque = .23(.42*9.8)sin(45) = Torque = .23(.60*9.8)sin(20)
Part III:
Test your prediction by pulling the bearing pin out and adjusting the second pulley and masses on the left side of the
sign until the left side of the sign is suspended. Quantitatively determine how well your values agree. Explain which
factor or measurement in the experiment is likely to have caused the measured discrepancy and why you think it is
the most likely factor.
510 g at an angle of 142
500 vs 510
40 vs 38
420 vs 415
45 vs 42
600 vs 610
20 vs 24
There are a lot of factors that could’ve caused discrepancies. It was hard to determine whether the sign was really
floating. There was friction in the pully. But overall our calculations were pretty close.
For help on lab equipment issues, please email [email protected], call 801-422-5393, or come to room N490 ESC.
In case of life-threatening emergencies, immediately call 801-422-2222.