Vectors Practicum I
Goal:
The purpose of this practicum is to gain experience in adding vector quantities
experimentally, graphically, and computationally.
Suppose we were adding the effects of


two forces FA and FB .
 
FA  F B

FB

FA



 F  net force  FA  FB
In this case the net force could also be called a resultant force, the one force that
has the same effect on a body as the vector sum of two or more other forces.
Vectors Practicum I
What if we instead wanted to determine the one force that would balance out the first
two forces?

FE

FA

FB
Notice that the equilibriant
is the same size but in the
opposite direction of the
resultant!

F  0



FE  FA  FB  0



FE  FA  FB 

Where FE  Equilibriant
Equilibriant – the one force that balances one or more other forces and thereby
results in an object in equilibrium
(Equilibrium occurs when the vector sum of the forces is zero)
Vectors Practicum I
 For each case, hang the given masses at the stated angles. Be sure to include
the mass hanger (m = 5.0 g = 0.0050 kg) in the total mass.
 All directions are measured using counter-clockwise from 0° notation.
 Adjust the pulleys downward until the strings are close to but not touching the top
surface of the force table.
Vectors Practicum I
 By trial and error, find the angle for the third super pulley clamp and the mass that
must be suspended over the pulley so that its weight will act as the equilibriant
and balance the forces exerted on the strings by the other two masses. Record
as the Experimental Equilibriant.
 Remember that the resultant must be the same size as the equilibriant, but in the
opposite direction. Record the Expermental Resultant.
Vectors Practicum I
Experimental Method of Finding Equilibrium
 The knot should be centered over the hole in the middle of the center post when
the system is in equilibrium.
 The anchor string should be slack.
 Pull the knot slightly to one side and let it go. Check to see that the knot returns to
the center. If not, adjust the mass and/or the angle of the super pulley clamp until
the knot always returns to the center when pulled slightly to one side.
Vectors Practicum I
 Compute the resultant both computationally and graphically (chose a scale).
Record the results and calculate the percent error for each compared to the
experimental value. Everyone should complete the worksheet, with one set for
the group to be turned in at the end of the hour. PSYW
Theoretical  Experimental
% Error 
 100
Theoretical