Vector Lab
Name:
Date:
Introduction: When two or more forces act on an object to produce motion or
equilibrium they are called concurrent forces. The single force that produces the
same effect as the concurrent forces acting together is known as the resultant.
The process of finding the resultant is called the composition of forces. Two
concurrent forces may be balanced by a third force, called an equilibrant. The
equilibrant is equal in value, but opposite in direction to the resultant.
The resultant of two concurrent forces acting at any point can be found by
the head to tail method. In this method, the size and direction of the forces are
represented by arrows drawn to scale.
Objective: To find the resultant of two concurrent forces and compare it to the
equilibrant of those forces in two different setups.
Apparatus: force board, spring scales, 200 g mass, protractor, ruler
Procedure:
Setup 1:
1) Examine each spring scale to assure that it reads zero when there is no
load attached to it.
a. If it does not you must add or subtract this amount from your
readings (if greater – subtract, if less – add).
2) Attach on end of each spring scale to a point of support on the force
board. (As shown in Diagram 1) Adjust the scales so that a considerable
amount of force is being exerted on each. Record those readings (adjusted
for zero error).
3) Place a blank sheet of paper on the force board and underneath the scales,
so that the point of intersection, O, is in the center of the sheet. Draw a
line that shows the direction of each force. Label these lines A, B, C .
Remove the sheet of paper. If the lines do not intersect at point O, try
again using another sheet of paper.
4) Using a suitable scale such as 1cm = 50 g, draw your force vectors (OA,
OB, OC) to scale on your paper. Measure the angles between these forces.
5) Attach the tail of OB to the head of OA (Remember: to move vectors they
must maintain size and direction!)
6) Draw the resultant, OD from the tail of OA to the head of OB.
7) Compare the size and direction of OD, the resultant, to OC, the
equilibrant.
Spring scale A
Mass
(Vector C)
Spring scale B
Ring stand
Setup #2
1) Set up apparatus above using a 200 g mass as your “sign”
2) Record each scale reading in grams
3) Record the angle (Ø) that the 2 strings make with each other
4) In your lab notebook draw a scale diagram of the 3 vectors that are adding
up to produce equilibrium.
5) Add vectors A and B graphically to prove that they equal vector C
6) Show all calculations including percent error for each case
NOTE: Both set-ups are very tricky to do. Take your time and measure
accurately.
Data:
Setup #1
Spring scale A =
length of vector OA =
Spring scale B =
length of vector OB =
Spring scale C =
length of vector OC =
Length of Vector OD =
Value of OD (g) =
Setup #2
Spring scale A =
length of vector OA =
Spring scale B =
length of vector OB =
Length of Resultant =
Value of Resultant (g) =
Questions:
1) What is a vector?
a.
2) OC is the (resultant/equilibrant) of the two forces, OA and OB
3) OD is the (resultant/equilibrant) of these two forces.
4) If two forces are parallel and act on an object in the same direction, the
resultant is equal to their
.
5) If two forces are parallel and act on an object in opposite directions, the
resultant is equal to their
.
6) What is the name of the method for adding vectors that we worked with
in this lab?
a.
7) Two spring scales, A and B, pull on a knot tied in a string. Scale A
registers 500 g and scale B registers 1200 g. Spring scale C, also pulls on
the knot and balances the other scales.
a. When A and B pull parallel to each other and in the same direction
spring scale C registers
.
b. When A and B pull at an angle of 90 degrees to each other, spring
scale C registers
.
8) Give two real life examples where you can see resultants and/or
equilibrants in action.
a.
Conclusion: