Notes for Density

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Unit 1 :- Measurement in
Physics
Learning Objectives
By the end of this section, you will be able to do the following:
• Associate physical quantities with their International System of Units (SI) and perform conversions
among SI units using scientific notation.
• Relate measurement to significant figures and apply the rules of arithmetic’s for using significant
figures in calculations.
• Using various appropriate scales to find appropriate physical quantities.
• Calculating unknown densities using the measurement of volume and mass using appropriate scales.
1.1 : Measuring units
The measurements of physical quantities are expressed in terms of units, which are
standardized values. For example, the length of a race, which is a physical quantity, can
be expressed in meters (for sprinters) or kilometers (for long distance runners). All
physical quantities in the International System of Units (SI) are expressed in terms of
combinations of seven fundamental physical units, which are units for: length, mass,
time, electric current, temperature, amount of a substance, and luminous intensity.
SI units (acronym for the French Le Système International d’Unités, also known as the metric system or
international system of units)

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In measurements, when dealing with very large or very small quantities, we need to
add ‘prefixes. These are symbols that are used to make the number smaller and thus
more manageable to use in further calculations. Here are some of the most common
type of prefixes:
Example of using prefixes

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Measuring Length:
Tool used : Ruler

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Measuring Time:

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Measuring Mass:

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Measuring Volume:
Solid
For a regular shaped object, we can find the volume by multiplying its length,
width and height as shown in the example below.
For an irregular shaped object, the volume is measured using the water
displacement method in a measuring cylinder.

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Liquid
For liquids, we use graduated
measuring cylinder, where we pour
the liquid and read the meniscus of
the level of the liquid.

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Finding Density

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Density Lab Investigation
In our Lab session, we investigated how the density of an
irregularly shaped object can be found. A simple example
is shown below to reiterate what was done in the lab.