1. Measurement involves comparing an unknown quantity to a known standard unit. The result of measurement has two parts - a number and a unit. 2. Originally, arbitrary units like handspans were used, but they varied between people. Standard units were introduced to maintain uniformity in measurement. 3. The International System of Units (SI) is the most widely used system, based on meters, kilograms and seconds as the standard units of length, mass and time.

1. VIDYA BHARTI EDUCATIONAL INSTITUTIONS
SCIENCE NOTES CLASS 6TH
MOTION AND MEASUREMENT
Measurement: Comparing an unknown quantity with some known quantity is
called measurement.
Result of Measurement: The result of measurement has two parts; one part is
the number and another part is the unit. The known quantity which is used in
measurement is called a unit. For example; when you say that your height is
150 cm then the measurement of your height is being expressed in a number,
i.e. 150 and a unit, i.e. centimeter.
Arbitrary Units of Measurement: Before the development of standard units of
measurement, people used arbitrary units of measurement. Some of them are
still in use at some places. Handspan, finger-length, cubit (length between the
elbow and finger tips), foot-length and arms-length are some examples of
arbitrary units of measurement.
Disadvantages of Arbitrary Units of Measurement: You have seen that arbitrary
units are made up of lengths of different body parts. These lengths can vary
from one person to another. This can create lot of confusion as there would be
no uniformity in measurement.
Standard Unit of Measurement
To maintain uniformity in measurement, standard units of measurement were
introduced in different parts of the world at different places. Napoleon is
believed to have introduced most of the standard units of measurement which
are being used today.
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2. VIDYA BHARTI EDUCATIONAL INSTITUTIONS
SCIENCE NOTES CLASS 6TH
MOTION AND MEASUREMENT
SI Unit (International System of Units): It is the most widely used system of
measurement in the world. It is based on MKS (Meter-Kilogram-Second)
System. Length, weight and time are considered as basic quantities for
measurement and other quantities are derived from them. As per SI system;
the unit of length is meter, unit of weight is kilogram and the unit of time is
second. Barring the unit of time, other units of this system are based on
decimal system. Use of the decimal system makes the SI Unit more user-
friendly.
Direct Measurement: When we measure some quantity directly, it is called
direct measurement. For example; when you are using a ruler to measure a
length, you are doing direct measurement.
Indirect Measurement: When we measure some quantity indirectly, it is called
indirect measurement. For example; when you have to measure the girth of a
tree or the length of a curve, you cannot use a ruler. You can use a rope to
find the length of a curved line and then compare the length on a ruler.
Correct Steps of Measuring the Length:
The scale should be placed along the length of the object to be measured.
The zero mark of the scale should be taken as the beginning point. If zero
mark is broken or invisible, then any other mark should be selected and final
adjustment should be made accordingly. For example; if you begin from 1 and
the final reading is 14 then actual reading would be 14 – 1 = 13.
Correct eye position should be maintained. The eye position should be just
above the point to be measured. Incorrect eye position leads to parallax error
and gives incorrect reading.
Motion: The change in position of an object with change in time is called
motion.
Types of Motion
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3. VIDYA BHARTI EDUCATIONAL INSTITUTIONS
SCIENCE NOTES CLASS 6TH
MOTION AND MEASUREMENT
Linear Motion: When the motion is in a straight line, it is called linear motion,
e.g. a car moving on a straight road.
Curvilinear Motion: When the motion is on a curved path, it is called curvilinear
motion, e.g. a car moving on a bend.
Circular Motion: When the motion is on a circular path, it is called circular
motion, e.g. the motion of the earth in its orbit.
Rotation: When an object moved around an axis, it is called rotation, e.g.
rotation of the earth on its axis.
Periodic Motion: When the motion is repetitive after a fixed interval, it is
called periodic motion, e.g. motion of a wing.
Story of Transport:
Early man used to walk to travel.
With the passage of time, man began using animals to transport people and
luggage.
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4. VIDYA BHARTI EDUCATIONAL INSTITUTIONS
SCIENCE NOTES CLASS 6TH
MOTION AND MEASUREMENT
Boats were probably built after seeing the shape of aquatic animals. Initial
boats were made by making hollow in wooden logs. The shape was later
refined into streamlined shape.
Discovery of wheel dramatically changed the modes of transport. Animal
driven carts could become a possibility after the discovery of wheel.
Steam engines brought the next big revolution in the modes of transport.
Steam engines altogether replaced the animal driven carts. Railways network
spread because of steam engines.
Internal combustion engines made it possible to replace steam engines.
Moreover, internal combustion engines also made it possible to make vehicles
for personal transport.
Jet engines helped in making the aircrafts faster.
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