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Mechanics
 
Aim: to measure the Relative Density of some common solids
The relative density of a substance is the ratio of the density of the substance to the density of pure water.
Therefore, the R.D. of a substance can be calculated by comparing the mass (or weight) of a given volume of the substance with the mass (or weight) of the same volume of pure water.
 
This writer feels that it is a good idea to remind ourselves that experiments can sometimes be performed with simple apparatus such as levers and bits of string...
 
The method suggested here is based on the observations made by Archimedes nearly 2000 years ago.
For the purposes of this experiment, the principle of Archimedes can be stated as follows:
When a body is under water, it experiences an apparent loss of weight equal to the weight of the water it displaces.
 
We first measure the real weight, W of a piece of the solid.
We then measure the apparent weight, WA of the same piece of solid when it is completely immersed in pure water.
From the preceding, it should be clear that the relative density can be calculated from the following equation
Method
Use a simple balance, as shown below.
Obtain an equilibrium first with the piece of solid in air.
This allows us to find the position of the mass, m, corresponding to the real weight, W of the object.
 
Next obtain an equilibrium with the same piece of solid immersed in water.
This allows us to find the position of the mass, m, corresponding to the apparent weight, WA of the object.
 
If we keep m and x constant for each pair of measurements, we can say that
and
therefore we can write
from which relative density can be easily calculated.
For each value of relative density measured, work out the indeterminacy in the result, assuming that the distances d1 and d2 are measured using a ruler marked in mm.
Then express your answers in the usual form: R.D. = x δx where δx is the indeterminacy.
 
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