Fiery Re-entry into Earth’s Atmosphere

First astronauts launched by SpaceX returned home safely on 3 Aug 2020.

Common SI prefixes

Physical Quantity is a quantity that can be measured and it consists of a numerical magnitude (size) and a unit. (e.g. 5m where 5 is the numerical magnitude and m is the unit)

1) The seven base quantities and their SI units

Out of the seven, for O level Physics, you are required to learn the first 5 (length, mass, time, current and temperature).

2) Some common derived quantities and units

You can think of base quantities as the smallest building blocks (like Lego bricks). When you combined any base quantities to ‘build’ into something else, they becomes a derived quantity.The derived quantity is ‘derived’ or ‘gotten from’ when 2 or more quantities are combined together.

3) Prefixes for SI units

Prefixes are used to represent very large or small quantities.For example, instead of writing 1000000 m, it will be more convenient to write 1Mm, which means the same thing!

Units conversion involving prefixes

Prefixes are used to simplify the writing of very big or very small numbers.

For instance, instead of having to write 12 500 000 m every time, you can simplify it by using the prefix mega (M), hence it can also be written as 12.5 Mm. Similarly, 0.00054 s can be written as 0.54 ms.

If you are unsure or confused with the unit conversions, you can refer to the following videos.

1) Prefixes can be used for different physical quantities units.

2) Unit conversion with examples

3) Unit conversion for units of area and volume

4) Unit conversion for units of speed and density