To verify Polygon Law of Forces by using Force Board.

AIM: VERIFICATION OF POLYGON LAW OF FORCES

APPARATUS:- Gravesands apparatus complete with two freely moving guide pulleys, weights, thread, a small central ring, white paper sheet, three scale pans, tape, a mirror strip, set squares, and pencil.

THEORY: Polygon law of forces states that if several forces acting on a particle are represented in magnitude and direction by the sides of a polygon taken in the same order then their resultant is represented in magnitude and direction by the closing side of the polygon taken in the opposite direction.

PROCEDURE:

1. Fix the paper sheet centrally on a board with the help of cello tape.
2. Tie five segments of thread to form a knot and pass four of them over the guide pulleys as shown in Figure LW-4.
3. Put four weights one each into the pans of the strings passing over the pulleys.
4. Attach a pan to the free end of the middle string and put weight into it.
5. Adjust the weights in the pans in such a way that the knot comes in the center of the paper and allows the system to come in the rest position.
6. Put the mirror under the threads turn by turn and mark the points by keeping the eye, the thread and its image in the same line without disturbing the system.
7. Write down the magnitude of forces in each string which will be the same as the corresponding weights.
8. Draw the vector diagram with suitable scale by drawing vectors ab, bc, cd, de representing magnitude and directions of corresponding forces AB, BC, CD, DE as show in fig. LW- 5(a)
9. Join e to a and measure vector ea with the chosen scale. It should have the same magnitude and direction as that of the forces EA.
10. The magnitude of ea is different from that of force EA, then the percentage of error = (𝐸𝐴−𝑒𝑎) × 100) / 𝐸𝐴
11. Repeat the above procedure at least two times more by varying loads and tabulate the results.

OBSERVATIONS:

Mean Value…………………………….

PRECAUTIONS:

1. The board should be perfectly vertical.
2. The pulleys should be moving freely and if not moving freely, lubricate them.
3. The weights should not touch the board.
4. The weights of the pans should be added to the weight in the pan to find the total force in each string.
5. The directions of forces should be marked only after the system has come to complete rest.
6. The direction of forces should be marked with the mirror strip by keeping the eye, string, and image in the same line.