Page 584 - SUBSEC October 2017_Neat

APPENDIX II
 PRACTICAL ACTIVITIES

The teacher is urged to reinforce the relevant approved codes and safety practices during the delivery
of all practical activities in the Module.

ARCHIMEDES’ PRINCIPLE

Refer to Unit 1, Module 1, Specific Objective 4.1 and 4.4

Aim: To determine the upthrust on an object totally immersed in water.

The balance you will use, illustrated in Fig. 1, consists of a metre rule suspended by a thread from a
retort stand and clamp.

Method: First, adjust the position of the thread on the rule so that it balances horizontally on
its own with no other masses suspended. Record the position of the thread.

Take the RUBBER stopper provided and suspend it by a thread close to one end of the metre rule.
Now balance the rule by suspending a 100g mass by a thread on the other side of the rule. The rule
should be horizontal when balanced. Record the point of suspension of the 100g mass.

When the rule is balanced, the principle of moments states that the sum of the moments of forces
about the point of suspension in the clockwise direction is equal to the sum of the moments in the
anticlockwise direction.

Draw a diagram indicating forces acting on the rule. Write an equation for the balance of the moments
of the forces. Hence, determine the mass of the stopper.

Q.1 Why balance the metre rule with nothing suspended at the start?

Leaving the stopper suspended from the same point, place a beaker of water below the stopper and
arrange it so that the stopper is completely immersed in water. Now find a new position for suspension
of the 100 g mass so that the rule is again balanced. Be careful to see that the stopper does not touch
the edge or bottom of the beaker. All the results should be carefully tabulated.

CXC A16/U2/17 84