Page 41 - Physics - XI

Motion in a Plane
2 Motion in a Plane

EXPERIMENT - 6

Aim

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

Apparatus and Materials Required

Gravesand's apparatus (parallelogram law of vector apparatus), two hangers, slotted weights, four sheets
of white paper, drawing pins, mirror strip, sharp pencil, metre scale, given body whose weight is to be
determined, strong thread, a set square, a protractor, and a spring balance

Description of Apparatus (Gravesand's Apparatus)

P P
1 2
Pulley C′ C Pulley

R′ R A
B P
Q O

Q X P

Block
Weight Weight

Fig. 6.1: Gravesand's apparatus

Gravesand's apparatus is used to determine the unknown weight of the body by verifying the parallelogram
law of vectors. The Gravesand's apparatus is shown in Fig. 6.1.

Principle/Theory

Parallelogram law of vector addition: It states that if two forces acting simultaneously on a particle are
represented in magnitude and direction by the two adjacent sides of a parallelogram drawn from a point,
their resultant is represented both in magnitude and direction by the diagonal of the parallelogram passing
through the point of application of two forces.
→
If a third force X is applied at the point of intersection of the two forces so that the common point of
application of all the three forces is in equilibrium, the third force is equal in magnitude, but opposite in
direction to the sum of the other two forces. This third force is known as equilibrant force.

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