Experiment no.
AIM :To verify the parallelogram law of forces and to determine the unknown weight.
APPARATUS :Gravesand's apparatus,two hangers with slotted weights,a body whose
weight is to be determined,thin strong thread,white drawing paper,drawing pins,mirror
strip,sharp pencil,protractor,compass,,metre scaLe
THEORY:
If an unknown weight body is suspended from the middle of the hanger and P and Q are two
balance weights from the other two ends of the hanger then the unknown weight is
calculated using the below equation
R=√P2+Q2+2PQcos ®
Where S is the unknown weight and P&Q are the balance weights.
DIAGRAM
PROCEDURE:
● Set up the apparatus with its board vertical with the help of a plumb line.
● Oil the pulleys if they are not friction less.
● Fix the white sheet I board with thehekp of drawing pins
● Let P&Q be the weights tied to two ends f thee hanger and S be the third weight tied
at the middle(let O be the junction)
● Junction O should be maintained at equlibrium by adjusting weights P &Q.
● All three weights act as three forces.they should hang freely without touching the
board.
● With the help of sharp pencil ,mark P1,P2,Q1,Q2,S1,S2 using plane mirror strip.
● Remove paper from board and use metre scale to join the above obtained points.
● Taking a scale 1 cm =50 gm,OA=3cm,OB=3 cm,to represent P=150 gm,Q=150 gm.
● r is represented by completing the parallelogram OACB
● Joining OC and measuring it
CALCULATIONS:
RESULT:the unknown weight of given body=___gm
PRECAUTIONS:
● The board should be stable and vertical
● There should be no friction in the pulleys
● The hangers should not touch the board
● Points should be marked when the weights are at rest.
SOURCES of ERROR:
● There may be friction in the pulleys.
● Weights might not be accurate.
● Spring balance may have error.
