Page 105 - Physics

Sinking and fl oating

2. Fill a measuring cylinder with water Task 5.4
to about 30 ml of its volume.
3. Lower the stone suspended at the end Suspend a slotted mass of 50 g by a
of the spring balance into the water. thread from a spring balance. Note the
3
It should be partially immersed. Note reading of the spring. Pour 60 cm of
the reading on the spring balance water into a measuring cylinder and
as w and the level of liquid in the immerse the suspended mass in water.
2
measuring cylinder. (Ensure that the mass does not touch
4. Lower the stone such that it is totally the walls of the cylinder). Record the
immersed in the water, as shown in readings on the spring balance and on
Figure 5.4 and record this weight as the measuring cylinder. Repeat the
w . same procedure using 100 g and 200
3
5. Remove the stone, dry and re-weigh g masses. Illustrate your work using
it in air. Record this weight as w . clear diagrams.
4
6. Calculate the apparent loss in weight
of the stone and record it as w . Archimedes’ Principle
L
7. Repeat steps 1 to 6 for other objects,
one at a time. If an object is immersed in water,
it displaces some of the water. The
Questions relationship between the upthrust acting

(a) What do you notice about the values on a body and the weight of the displaced
w , w , w , w , and w ?
1 2 3 4 L fl uid, when the body is partially or totally
(b) What is your conclusion about the immersed in the fl uid was discovered by
weight of the stone? a Greek scientist known as Archimedes.
This relationship is explained by

In Activity 5.2, you have learnt that, the Archimedes’ principle, which is referred
weight of an object in air ( w ) is larger to as the law of buoyancy.
1
than its weight when it is submerged in
water ( w ). That is, there is an apparent Archimedes’ principle states that,
2
loss in weight w ( ) which is the difference “Any object partially or totally
L
between the weight in air and the weight immersed in a fl uid experiences an
in liquid. Thus,
upthrust equal to the weight of the
Apparent loss in weight = fl uid displaced by the object”.
weight in air – weight in water.

w = w − w or w = w − w 3 It is important to note that the weight
1
L
1
L
2
of an object acts downwards while the
Note that the apparent loss in weight is
equal to the upthrust exerted on the object upthrust exerted by the displaced fl uid
by water. acts upwards.
99

Physics Form 1 Final.indd 99 16/10/2024 20:56