7/26/2019 Weight of Ruler by Moments

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Finding the weight of a ruler using moments

Apparatus:Metre ruler, knife edge, set of 100g masses [M20C]

Diagram:

Procedure:1. Place the metre ruler (without the weight shown in the aboe diagram! on the knife edge so that it is balanced.

"he knife edge should be roughl# below the $0cm mark on the ruler. %ote down the &recise &osition of the knife edge

below the ruler to the nearest mm. "his is the &osition of the ruler's centre of grait#.

2. Place a 100g mass, a weight of 1%, near the lefthand end of the ruler as shown in the diagram aboe.

"he ruler will ti& down on this side.

). Moe the knife edge towards the weight until the ruler again balances.

Measure the distance p(in mm! between the centre of the weight and the new knife edge &osition and the

distance q(in mm! between the new knife edge &osition and the &osition of the centre of grait# of the ruler

(see diagram aboe!.

*. +ecord #our measurements in a table with the headings shown below.

$. +e&eat stages 2 to * for weights of 2% (using 200g of mass! to % (00g mass!.

Calculations:1. -hen the ruler is balanced the anticlockwise moment caused b# the weight of the masses is eual to the clockwise

moment caused b# the weight of the ruler.

"herefore/

weight of mass, W (N) distance p (mm) ! ruler weight " (N) distance q (mm)

2. Calculate the alue distance, qdiided b# weight of mass , W #q $ W% for each of #our results in the a&&ro&riate column

in the table.

-eight of mass W

in newtons

istance p

(mm!

istance q

(mm!

qdiided b# W

(mm%!

). raw a gra&h of distance p(mm! [3456] against q $ W(mm%! [43456]

*. Measure the gradient of this gra&h.

"he gradient is eual to the weight of the ruler in newtons.

-rite out clearl# #our answer.

$. 78&lain wh# the gradient of #our gra&h euals the weight of the ruler

9" 21 :ctober 200) . 1.1

distance & distance .weight -

centre of grait# of the rulerknife edge

metre ruler balanced

on knife edge