Science Lesson #8: How To Measure & Calculate The Density Of Irregular Stone
An irregular stone is difficult to be measured since its dimensions aren't straight forward to use instrument like metre rule or tape measure to take all the dimensions. On like regular shape of a rectangular block or a table where one can view the length, the breadth and the hight, irregular stone has bent edges which makes it very difficult to be measured.
To be able to measure the density of irregular stone, two approaches are needed here in order to arrive by the correct measured.
Over here, unless specific quantity of mass and volume are given to be measured, one can choose any quantity of mass and volume. But, the standards units are the kilograms and cubic metre. Since I want to use small stone to be measured, I will choose grams and cubic centimeters to measure the density of my stone.
Measuring the mass of the stone
The mass of the stone is being measured using compression balance or top-pan balance. The figure is being recorded. For instance, the mass of the stone was being measured and recoded as 40g.
Measuring the volume of the stone
Since the volume of the stone can not be measured using rule or tape measure. A graduated measuring cylinder is used which measures in centimeter cube is used.
The graduated measuring cylinder is filled with water at the 20cm3 mark. This becomes the initial volume of the water and it's being recorded as volume 1 (V1).
A thread or a string is tied with the stone and lowered gently into the graduated measuring cylinder which contain the water. The water level rose from 20cm3 mark to 40cm3. This is recorded as volume 2 (V2), that's the Final Volume of the stone plus the water in the graduated measuring cylinder.
To get the actual volume of the stone, we have to subtract the Volume 1(V1) from the Volume 2 (V2). This leads us to some simple calculation:
The Actual Volume of the Stone= The final Volume of the Stone plus the water(V2) - The initial volume of the water alone (V1)
In simple terms:
The Volume of the stone=V2-V1
The Volume of the stone=40cm3-20cm3
The Actual Volume of the stone=20cm3
Measuring the density of the irregular stone
Density is defined as the measure of mass per unit volume of a substance.
Mathematically it's expressed as Density = Mass/Volume
So, the Density of the measured irregular stone becomes:
Density of the stone= 40g/20cm3
Density of the stone = 2g/cm3
Hence the Density of the irregular stone = 2g/cm3
I think this method is very simple. But what students should note is that in terms of the units, the standard units of density are kilograms and Cubic metre ( Kg/m3). Kilograms moves with metre cubic, grams goes with centimeter cubic and milligrams goes with millimeter cubic. For instance if in measurement of Density you are given to measure in grams and the volume is given to measure in metre, it means you have to quickly change or convert the unit of grams to kilograms to match with the metres
Precautions that should be taken when measuring the density of irregular stone
1• The graduated measuring cylinder should be position well to avoid splashing of the water from the graduated measuring cylinder. If splashing of water happens you wouldn't get accurate measurements.
2• The string or thread should be tied with the stone well and gently immerse in the water to prevent inaccurate measurements.
3• Students should be critically observe, read and record the figures of the volume and mass to help accurate calculation of density.
If students are able to follow the right principles and procedures of measuring the density of irregular stone, it would help them to excell in their exams and every day life.
if students can stick to the precautions, they will get accurate calculation of density. This method is simple and well detailed.
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