CP Science 9

Force Vectors and Angles Lab

 

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INTRODUCTION:

Force has magnitude and direction and, therefore, is a vector.  The rules for vector addition that you learned in the last chapter can be applied to force vectors. The force necessary to hold an object at equilibrium changes with the angle of the vector.

 

PURPOSE:

In this lab you will measure the force vectors in different situations and at different angles.

 

MATERIALS:

2 Iron supports             1 meter stick                 1 250-g mass

2 clamps                                   1 protractor                  2 strings (each about 10-20 cm long)               

2 500g or 1000 g scales                                              

 

 

DATA RECORDING:

1. Mass used: ______ g. Its weight is ________ Newton. Show conversion set up in the space below.

 

2. String 1 length: _________ cm; string 2 length: _________ cm.

 

3. Copy the DATA table template below.  You will need 7 rows in total to accommodate all the data.

 

Setup Number

Angle (degrees)

Scale 1 Reading (g)

Scale 1 Reading (N)

Scale 2 Reading (g)

Scale 2 Reading (N)

Average Tension Force (N)

1

(one string)

 

 

 

 

 

 

2

(two strings)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

PROCEDURE:

 

Setup 1 (1 string):

1.      Hang both spring scales from one string, one after the other, from the midpoint (the “50” cm mark) of the meter stick.

2.      “Zero” the scales if necessary.

3.      Hang the mass from the last scale, shortening the string length as necessary so the mass does not touch the table.

4.      Read and record the scale readings in g on your data table in the boxes for reading 1 and 2. 

5.      Using your protractor, verify that the string hangs at a 90 degree angle with the horizontal (crossbar) and enter that in the table under angle.

Setup 2 (2 strings):

6.      Move both strings to near the “50” cm mark (+1.5 cm) of the meter stick. Hang one of the scales from the end of each string.

7.      Tie the bottom of the two scales together loosely, leaving some length of string in between.  Make sure the scales hang parallel to each other as in the figure to the right.

8.      Zero the scales if necessary.

9.      Hang the mass from the string, read and record the forces on each scale in g.

10.  Measure the angle the string makes from the meter stick, and record the angle.

 

Setup 3:

11.  Remove the mass.

12.  Carefully slide the two strings to “40” and “60” cm marks, respectively.

13.  Hang the mass, read and record the forces on each scale in g.

14.  Measure the angle the string makes with the meter stick from the point at which the string is attached to the meter stick, and record that angle.

 

Setup 4-6:

15.  Repeat steps 11-14 while slide the two strings to “30”/“70”, “20”/“80”, “10”/“90”, respectively. Hold the strings on the meter stick at the right positions to prevent them from sliding off.

 

DATA ANALYSIS:

 

1.      Convert each force reading in g to N (Newton) in your data table. Calculate the average tension force in Newtons in the strings.  Record the results in the appropriate columns on the table.

2.      Make a line graph from setup 2-6 showing average tension force (y-axis) versus the angle (x-axis) by plotting the angle and average tension force data and curve-fitting the data points with a “best fit line”.  (Hint: your x-axis should go from 90 to 0).

3.      What is the shape of the graph of force versus angle?

4.      In setup 2, how did the scale readings compare when two strings were used instead of one as in setup 1?

5.      As you moved the strings farther apart, what happened to the tension force on the strings?

6.      In setup 3-6, as the strings were moved further apart, how did the tension force on each string compare to half of the weight of the mass?

7.      What kind of setup would most likely break the string?

8.      From your graph, what would the force be at 75o?

 

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