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Physics

SI base units

Physical quantity Unit name Unit symbol
mass kilogram kg

length metre m
time second s
textbooks nis edu kz
temperature kelvin K
electric current ampere A

INV Attempt to measure your desk, this textbook and the length of the room using your
own unit of measurement. Discuss your results with your classmates. What do you notice
about your results? How could you improve this investigation for the whole class?

Accuracy and errors in measurements
When you measure using any device, you should determine the accuracy of your
measurement. We have already seen that every device has its own scale. Every scale has
divisions. This is the distance between one mark and the next. Marks on a scale are labelled by
numerical values. But it is inconvenient to label every mark. Therefore you should know how
to determine the scale division value of a device. This is the minimum value that a device
can measure. What is the scale division of each ruler shown at the start of the lesson?

The accuracy of a measurement depends on the scale division value of the device you are
using. The smaller the scale division value of a device, the more accurate the measurement .
When thinking about accuracy we must also consider any errors we might make when taking
our measurements.

Writing numbers in standard form

While exploring everything around us, sometimes we have to take measurements of quite
different values. Sometimes measurements have small values. For example, mass can be
measured in grams and length in millimetres. But sometimes measurements have very
large values, for example, mass in tonnes or length in tens or hundreds of kilometres.
Special prefixes are used for convenience in such cases.

Multiple prefix Fractional prefix
hecto 10 2 h centi 10 -2 c

kilo 10 3 k milli 10 -3 m
mega 10 6 M micro 10 -6 µ

OVER TO YOU!

1. The mass of a blue whale is around 150 tonnes. Express this
number in kilograms and write it in standard form.
2. Do it at home! Find 3 measuring instruments at home.
Record their maximum and minimum measurements. What is the
minimum scale division of each instrument? What is its unit of measurement?

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