To find the weight of a given body using parallelogram law of vectors.

APPARATUS SUPPLIED WITH EXPERIMENT 

1. GRAVESAND'S APPARATUS (PARALLELOGRAM APPARATUS)
2. SLOTTED WEIGHTS (50GMS*5, 3 SETS
3.  2 Z PULLEYS
4. WHITE DRAWING SHEET
5. DRAWING PINS
6. MIRROR STRIP 

This is Gravesand’s apparatus or Parallelogram apparatus.  It consists of a wooden board A fixed vertically on two pillars. There are two Z pulleys P and Q fitted at the same level at the top of the board. Three set of slotted weights are supplied with the apparatus which can be used to verify the parallelogram law of vectors.  A thread carrying hangers for addition of slotted weights is made to pass over the pulleys so that two forces P and Q can be applied by adding weights in the hangers. By suspending the given object, whose weight is to be determined, in the middle of the thread, a third force W is applied.

If  two vectors acting simultaneously on a particle are represented in magnitude and direction by the two adjacent sides of a parallelogram drawn from a point, then their resultant is completely represented in magnitude and direction by the diagonal of that parallelogram drawn from that point. Then the diagonal , will represent the resultant R in magnitude and direction. By applying vector addition formula we can determine the unknown weight.