Lab Exercise- Vector String



Lab Exercise- Vector String

Carol Brunjes, Kenneth Harvey, James Havens

07/02/02

Objective: To understand the components of vector addition.

Equipment:

• 2- Three (3) meters high visibility, low stretch string

• Protractor

• 1-3 meter sticks

• Masking tape

Procedure:

1. Tape end of one of the strings to the floor

(Figure 1, point A)

2. Choose a spot somewhere near the middle of the string

and tape it to the floor at that spot (Figure 1, point B)

3. Tape other end of string to the floor (Figure 1, point C)

4. Measure segment AB, record in data table

5. Measure segment BC, record tin data table

6. Measure angle B, record in data table

7. Hold second string from point A to point C

8. Measure angles A and C, record in data table

9. Measure length AC, record in data table

10. Use Law of Cosines to determine AC

11. Calculate errors

12. Repeat five times with different angles at B

Alternate: Use the same concept to introduce position vectors, by using x1,y1 for A, x2,y2 for B and x3,y3 for C. You can use the tiles in your room or hallway to establish a grid.

Discussion:

The total length AB + BC is constant however, the length AC changes as angle B changes. The distance AC is NOT the algebraic sum of the AB and BC but the vector sum of AB and BC. The vectors may be added by triangulation, competition of parallelogram, or component vectors.

Questions for Students:

1. Explain why the length AC is not the math sum of AB and BC.

2. How does the length AC change as the angle B changes

3. Discuss the reasons for your errors

References:

-----------------------

A, y1, (x2, y1

C

B

Figure 1

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