# EXPERIMENT

### OBJECTIVE:

To verify the law of polygon of forces with the help of universal force table apparatus.

### APPARATUS:

Universal Forces table with five pulleys, rings with five string weight, slotted weight, plain paper and geometry box.

### THEORY:

Polygon law of forces states that if a number of concurrent forces are acting simultaneously on a body, are represented in magnitude and direction by the sides of a polygon, taken in order, then the resultant is represented in magnitude and direction by the closing side of the polygon, taken in opposite order. ### PROCEDURE:

• Before starting the experiment make the graduated table horizontal with the help of leveling screw.
• Clamp the pulley to the graduated disc of the force table.
• Tie one and of thread to the circumference of small rings and place it around the central axis of the apparatus.
• Attach other end of the string to the weight hangs which will carry small slotted weight.
• Pass one string over each pulley.
• Place slotted weight on the weight hanger in such a manner that ring is placed around the center.
• Note down the angle between different threads and corresponding weights.
• Draw a space diagram of the force acting a part such that the time of action of each force corresponding to the angles of forces between them.
• Chose a suitable scale and make mark a point on a paper and draw the vector diagram of force system acting at a point by drawing parallel line of each force proportional to the chosen scale.

Procedure to draw vector diagram:

• Draw a line OA parallel and equal to W1 assuming a suitable scale.
• Draw a line AB parallel and equal to W2 from point A assuming the same scale.
• Similarly draw BC and CD parallel and equal to the force W3 and W4.
• Join OD i.e. the closing side by dotted line, which represents the resultant of polygon (graphically).
• Measure the line OD and compare it with W5 by using the same scale.
• Find the error by using the formula given in the observation table. Error should be positive.

### OBSERVATION TABLE:

 FORCE (in grams) ANGLE ( in degree) S. No. W1 W2 W3 W4 W5 θ1 θ2 θ3 θ4 θ5 RESULTANT OF FORCES (R) (OD) ERROR IN % (W5 –R)/W5 x 100 or (R- W5)/R x 100

### PRECAUTIONS:

• Ring should not touch the control axle of the disc and should be at the center of the table.
• Positions of the strings should be at the center of the table.
• Pulley should be frictionless.