Page 101 - Physics
P. 101
Sinking and fl oating
action of weight and the upthrust on an that determine whether it sinks or fl oats,
object in the fl uid is shown in Figure 5.2. and discuss any possible methods to
Upthrust make it sink.
Acti vity 5.1
Aim: To demonstrate sinking
Weight
and fl oating of objects.
Figure 5.2: Forces acting a body Materials: Various objects of
submerged in a liquid
different shapes and sizes
In Chapter Two, it was shown that when an (examples are metal
object is immersed in a fl uid, it displaces a spoon, plastic bottle cap,
volume of the fl uid equal to the volume of wooden block, rubber ball,
the body. It is also shown in the previous Aluminium foil, toy boat),
section that the upthrust acting on the large container fi lled with
immersed object depends on the volume water (a basin or a bucket)
of the object and the density of the liquid and paper pencil.
in which it is immersed. Therefore, sinking
and fl oating can also be explained in terms Procedure
of the density of the object and that of the 1. Predict which object will sink and
fl uid. which one will fl oat. Record your
results.
If the object’s density is greater than that 2. Fill the container with water.
of the fl uid, the object will sink. The 3. Wear sanitary gloves, and gently
object fl oats if its density is less than that put an object in the water at a time.
Observe if it sinks or fl oats.
of the fl uid. Ships and boats fl oat on water 4. Repeat the step 3 for every object at
because their average density is less than your disposal.
the density of water. Infl ated balloons fl oat
in air because their average densities is less Questions
than the density of air. Metallic objects, (a) What do you notice about the objects
such as spoons and coins, sink in water that sank?
because they have higher average densities (b) What do you notice about the objects
than the density of water. that fl oated?
(c) Were there any surprising results
Task 5.1 or objects that didn’t behave as you
The density of aluminium foil is 2.7 predicted?
times that of water. Take a piece of foil, (d) In terms of density compare the
shape it into a ball, and place it in water, objects that sank and those which
will it submerge? Explain the factors fl oated.
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