Physics Force Table Lab Report

Vector Addition Experiment 1 Physics 126 Vector Addition

Equipment Needed Equipment Needed


Super Pulley Force Table (ME-9447B)

Super Pulley Table Clamp (ME-9448B)

Mass and Hanger Set (ME-8979)

Mass Balance (SE-8723)

String (spool of thread)


Metric Ruler

Sheet of paper (2)



The purpose of this experiment is to use the force table to experimentally determine the force that balances two other forces. This result is checked by adding the two forces using their horizontal and vertical vector components, and by graphically adding the force vectors.


This experiment finds the resultant of adding two vectors by three methods: experimentally, by adding compo- nents, and graphically

NOTE: In all cases, the force caused by the mass hanging over the pulley is found by multiplying the mass by the acceleration due to gravity, 9.8 m/s2.

Experimental Method

Two forces are applied on the force table by handing masses over pulleys position at certain angles. Next, the angle and amount of mass hanging over the third pulley are adjusted until the force from this pulley balances the forces from the other two pulleys. The third force is called the equilibriant ( FE ) because it is the force that establishes equilibrium. The equilibriant is not the same as the resultant ( FR ). The resultant is the addition of the two forces. The equilibriant has the same magnitude as the resultant, but it is in the opposite direction of the resultant because it must balance the resultant. The equilibriant is the ‘negative’ of the resultant.

–FE = FR = FA + FB
















1. Assemble the force table as shown in the Assembly section. Use three super pulley clamps (two for the forces that will be added and one for the force that balances the sum of the other two forces).

2. Arrange the strings from the String Tie over the pulleys.





Force table set up





3. Hang the following masses over two of the super pulleys and clamp the pulleys at the given angles. You will repeat this for atleast three more different angles and masses.

Table 1.1:

Force Mass Angle
FA 50 g (0.050 kg)
FB 100 g (0.100 kg) 120°
FE 86 g (0.086 kg) 270°

Procedure (Experimental Method)-This is Method 1

By trial and error, find the angle for the third super pulley clamp and the mass that must be suspended over the pul- ley so that its weight will balance the forces exerted on the strings by the other two masses. This third force is called the equilibriant ( FE ) because it establishes equilibrium. The equilibriant is the negative of the resultant.

Record the mass and angle for the third pulley to put the system into equilibrium into Table 1.1.

To test whether the system is in equilibrium, use the following criteria.

Method of Finding Equilibrium

The clear disk will be centered in the String Tie when the system is in equilibrium. Pull the clear disk slightly to one side and let it go. Check to see that the disk returns to the center. If not, adjust the mass and/or the angle of the super pulley clamp until the disk always returns to the center when pulled slightly to one side.


To theoretically determine what mass should be suspended over the third pulley, and at what angle, calculate the magnitude and direction of the resultant by the component method and the graphical method. The equilibriant ( FE ) will have the same magnitude, but it will be opposite in direction. In other words, the direction will be 180° from the direction of the resultant.

Component Method-This is Method 2

On a separate sheet of paper, add the vector components of Force A and Force B to determine the magnitude of the equilibriant. Record the components Rx and Ry in Table 1.2. Use trigonometry to find the direction of the equilibriant (remember, the equilibriant is exactly opposite in direction to the resultant.) Record the results in Table 1.2.

Graphical Method-This is Method 3

On a separate sheet of paper, construct a scale tail-to-head diagram of the vectors of Force A and Force B. Use a

metric ruler and protractor to measure the magnitude and direction of the resultant. Record the results in Table 1.2. Remember to record the direction of the equilibriant as opposite in direction to the resultant..

Table 1.2:

  Equilibriant ( FE )
Method Magnitude Direction

Rx Ry =




Your instructor will give you an unknown mass. You need to create a setup and determine the unknown mass.

You must use atleast two hanging masses. You will need to get within 2 % to finish the lab. The instructor will give you a range that the unknown mass could be. In your lab write up make sure to include an error analysis.

Lab write up should include the five setups used in this lab and the three different methods of calculating the resulting force.





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