PhysicsLAB Lab
Static Equilibrium Lab

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Purpose: In this lab we will experimentally calculate the mass of a suspended weight by placing the weight in static equilibrium and measuring the tension in 6 locations.
You will need the following materials: one piece of string approximately 90-cm long, one trapeze with a horizontal bar and two sliding clamps, two 2.5-newton spring scales with a 350-grams of mass or two 5.0-newton spring scales with a 500-gram mass, and two meter sticks.
To begin, record the following information in the blanks provided below.
Refer to the following information for the next two questions.

Control Values
mass of suspended weight in grams 

height of horizontal beam above the top of the table in cm 

Next we will position the two sliding clamps at six different separation distances. At each separation, hang the weight from the string and adjust the mass' position until the spring scales have the same reading. Measure the tension on each spring scale and record your answer to two decimal places. Next measure the distance from the TOP of the hooked mass to the top of the table. Record your measurements in the data table provided.
Refer to the following information for the next six questions.

Data Table
separation distance height above table tension in
(cm) (cm) (N)
Refer to the following information for the next nine questions.

Analysis and Conclusions:  By subtracting the height of the hook of the hanging mass above the lab table from the height of the bar above the lab table, we can calculate the vertical displacement of the suspended mass. By dividing the distance between the sliding clamps in half, we can calculate the horizontal displacement of the suspended hooked mass. These measurements will give us the tangent of the angle between the bar and the spring scales.
Once we know the tangent value, we can calculate the angle and any other required trig values.
Examination of the hanging mass reveals the following freebody diagram centered on the hook at the top of the suspended mass.
Since the position of the mass was adjusted until the tensions on the two spring scales were identical, the horizontal components, T cos(q), cancel each other. The equation for vertical equilibrium based on our freebody diagram is shown below.
In our experiment, the tension, T, was the dependent variable while the angle, q, was the independent variable. The final equation shown above represents the theoretical equation for our line.
Open the EXCEL file 1-staticequilibrium.xls and enter your data recorded in your data table.
What was the name of your file saved on the filesystem for this lab?

What was the numerical value of the slope of your line? 

According to the FBD, how many forces were acting on the hook of the suspended mass? 

Explain why we graphed T vs csc q instead of T vs sin q.

Based on your equation, what does the slope of your line represent?

What was the experimental mass of your suspended weight in grams? 

What is your experiment's percent error? 

What was the average value of your six vertical components on your EXCEL sheet? (see column I) 

What does this average represent?

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