Parallelogram Law of Vectors Aim: To find the weight of the given body
using the Parallelogram Law of Vectors Let’s understand the main parts of Gravesend�s
Apparatus. Place a paper on the wooden board.
Take pins from the box. Firmly fix the paper on the board using the
pins. Take a thread and pass it over the pulleys
and hang equal weights, say, 20grams, to both ends. Mark it as P and Q. An unknown weight
attached to a third string is tied to the middle of the first thread and marked as O
and S. Hang another 20 grams to both ends.
Place a mirror strip beneath the thread and mark the points with a pencil at the edges
of the mirror where its image coincides. Do this for other two threads.
Remove the paper from the board by releasing the pins.
Place it on the table. Join the marked points with a pencil and a
scale. Assuming a scale of 20 grams, OA=4 centimeters,
OB=4 centimeters to represent P=80 grams weight and Q=80 grams weight respectively. Measure
the either sides of point O with a scale. Measure 4 centimeters on a compass using a
scale. Draw an arc from point B and another arc from
point A joining the previous one and mark it as C. Complete the parallelogram AOBC.
Draw OC. It is found that OC=4.3 centimeters Record the observations in the observation
table. Measure the angle AOB with the help of protractor
and note it. Complete the tabular column with the observations
. Unknown weight, S is equal to eighty six grams
weight. Unknown weight, R is equal to eighty five
point nine six grams weight. Unknown weight is equal to S plus R divided
by two. That is equal to eighty five point nine eight
grams weight. Which is equal to eighty five point nine eight
into ten raise to minus three kilo gram weight.