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Density and relative density
Determination of density of solid Example 4.3
The density of a solid object can be
determined using techniques that depend on In a physics exercise, a student was given
the shape of the object under observation. a rectangular shaped block to fi nd its
The shape of the object may be regular density and predict using a standard
or irregular. For the case of regular density table the type of material
shape, one needs to measure its mass and composing the block. The student
dimensions. The density is then calculated measures the mass and dimensions
m of the block and obtained 150 g and
using the formula ρ = , where volume
V 3 cm ×4 cm ×5 cm, respectively. What
is calculated using the dimensions of possible conclusion did the student
the objects. If the shape of the object is make?
irregular, its volume can be measured Solution
using the measuring cylinder or eureka can Mass =150g
as discussed in Chapter Two of this book.
Volume = 3 cm × 4 cm ×5 cm
Acti vity 4.2 = 60 cm 3
Aim: To determine the density Mass 150g
of regular shaped objects. Density = Volume = 60 cm 3
Materials: Wood blocks, glass = 2.5 g/cm or 2 500 kg/m .
3
3
block, textbooks, ruler
and test tube This value is the same as the density
of glass (see Table 4.1). Therefore, the
Procedure block is made of glass.
1. Measure and record the length,
height and width of each object. Task 4.1
2. Measure and record the mass of each
object. Suppose, you have a wooden block, metre
3. Calculate the volume of each object ruler, and a beam balance and you want
using a proper formula. to determine the density of the wooden
4. For each object calculate its density. block:
5. Report your results in a tabular form. (a) What information do you need in
order to calculate the density of the
wooden block?
Question (b) How would you obtain such
Compare the densities of different information using the available
objects. resources?
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