Measurements Notes 6th Science Lesson 1 Notes in English

6th Science Lesson 1 Notes in English

1] Measurements

Introduction:

• We have already heard about the words like weight, kilogram, litres, millilitres, kilometre, length, distance etc.
• we have a deeper look at length, weight, volume and time and the necessity to measure them.
• The comparison of unknown quantities with some known quantities is known as measurement. Measurement of a quantity has two parts: a number and its unit.

Length

• The distance between one end and the other desired end is called as length. It may be the distance between the edges of a book or a table or the corners of a football ground or even from your home to school.
• The standard unit of length is ‘Metre’. It is represented by letter ‘m’. Very small lengths can be measured in mm and cm.
• Still larger measures, say height of a building, a banner or a lamp post are all measured in metre. It is expressed in kilometre (km).

Know the unit of length

• 1 km (kilometre) = 1000 m (metre)
• 1 m (metre) = 100 cm (centimetre)
• 1 cm (centimetre) = 10 mm (millimetre)

Why do we need SI Units?

• The sake of uniformity, scientists all over the world have adopted a common set of units to express measurements.
• This system is called as the International System of Units or SI Units.
• SI unit for length is Metre
• SI Unit for mass is Kilogram
• SI Unit for time is Second
• Area of Surface = m²
• Volume of Solid = m³
• Multiples and sub multiples of SI Units. Prefixes used in SI Units. (Always remember the base unit is metre, litre, kilogram)

Corrective Measures for Measurement

• Measurement has to be accurate and the approach has to be correct always. In our day to day life approximation may not have much impact. But it has a large impact in scientifi c calculations.
• For example, if the curvature of key (lock and key) is changed by even 1 mm, the lock would not open.Let us look at some common mistakes that occur while using a scale.

To measure the length of a pin using a scale

• The head of the pin has to coincide with ‘0’ of the scale.
• Count the number of centimetre and from there count the number of finer divisions. The count of the division is ‘mm’
• In the above example the length of pin is 2 cm and 6 mm.

• Take care to write the correct submultiple

• Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight.

• Correct position of the eye is also important for taking measurement. Your eye must be exactly in front of vertically above the point where the measurement has to be taken. In the above representation, to avoid parallax error, reading will be correct. From positions ‘A’ and ‘C’, the readings will be different and erroneous.

Volume

Volume of Solids

• Length is a fundamental quantity. That means, it connot be expressed in any other quantities. Using length, we can find out other measurements like Area and Volume. Area is obtained by using two lengths.
• So, Area = Length × Breadth. Now, you can guess how to measure the area of your text book, your classroom or your playground.

• Volume is also a derived quantity and it can be measured from measuring lengths. Let us calculate volume of a box. To know the volume of a box we need to know the length (l), breadth (b) and height (h).
• With a measuring scale measure the three parameters in cm. The volume of the box = l × b × h. Unit of volume would be obviously cm × cm × cm = cubic cm or cm3.

Volume of Liquid

• Measuring the volume of a liquid is quite easy. Liquids take the shape of the container in which they are kept.
• A liquid whose volume is to be found can simply be poured into a graduated container.
• Graduated cylinders, beakers, pipettes and burettes are available for measuring exact volumes.
• The volume of liquid is usually measured in litres.We would have often heard the word litre in our daily life. For an example 1 litre milk packet, 20 litres water can.

Measuring the volume of objects with irregular shape

• There is no mathematical formula to measure this but there are many ways to do. Remember, volume is the space occupied by an object. We can use this property to measure the volume of an object with irregular shape, for example a stone.
• Let us try to find volume of a small piece of stone.Fill a graduated measuring cylinder with water to certain level, say 50 ml.
• Tie the stone with a piece of fine thread.Immerse the stone completely into water. As the stone is immersed, we can observe that water level increases.The stone displaces the water to occupy the space inside the measuring cylinder. It would be equal to the space taken up by stone.
• So the amount of water displaced will be the volume of the stone. This method is called as water displacement method. Suppose initially the water level was 50 ml. After you immerse a stone the water level rises to 75 ml.

Volume of the water displaced is 75 ml – 50 ml = 25ml

1ml = 1 cubic cm

25ml = 25 cm3

the volume of stone = 25cm3

Volume of gas

• We can also measure the volume of gases. Gases expand to fill the container into which they are placed. When you compress, a gas you can make the same gas to occupy lesser space. (as in LPG gas cylinder).
• Therefore it is not easy to talk about the volume of gas in the same way as a volume of a stone or a liquid. It is essential to take into account the pressure at which the gases are kept.
• We will learn about these later. SI unit for Volume of solid is cubic metre. Liquids and gases are usually measured in litres. But also can be measured in m3 or cubic metre. Similar to the length,
• 1 m³ = 1 kilolitre (kl or kL)
• 1cm³ = 1 millilitre (ml or mL)
• 1mm³ = 1 microlitre (µl or µL)

Mass

Mass and Weight

• Mass is the measure of the amount of matter in an object. Weight is the gravitational pull experienced by the mass. Hold a sheet of paper in one hand and a book in another.
• The mass of the book is more than that of a single sheet of paper. Therefore the pull on the book is more than that of the paper.Hence our hand has to give more force to hold a book than a paper.
• This force is what we experience as ‘heaviness’.The SI unit of mass is kilogram. It is represented by the ‘kg’.

Bigger weights are measured in tonne or Metric Tonne.

• 1000 milligram = 1 gram
• 1000 gram = 1 kilogram
• 1000 kilogram = 1 tonne

Beam Balance

We use beam balances to measure mass. A beam balance works by comparing the mass of an object to that of known mass (called a standard mass)

Electronic Balance

• An electronic balance is a device used to find accurate measurements of weight. It is used very commonly in laboratories for weighing chemicals to ensure a precise measurement of those chemicals for use in various experiments.
• Electronic balances may also be used to weigh food, other grocery items, as well as jewellery.

Time

• Day changes into night and night in to day. Seasons also change. Clocks are used to measure time. You know how to read a clock face and note the time. You can also use your pulse to measure ‘rough’ time.
• Count the number of pulses. That can tell you the time elapsed. In your normal speed of speaking, say “one little second”; “two little second” to count the passage of time.

More to Know

• The weight is directly proportional to the mass on earths surface. On moon where the gravitational force is lesser than earth, the weight will reduce but the mass will remain same. The moon’s gravitational pull is one sixth of the earth’s pull. Thus objects weight six times lighter on the Moon than on the Earth.
• In earlier days people used sand clock and sundial to measure the passage of time during the day. The shadow cast by a stick can be used to estimate time. One can also use a vessel with a small hole for computing time. Take a vessel or bottle with a small hole in it and fill it with water. The time taken for water to drain can also be used as a measuring device.
• These are rough methods for counting passage of time. We can use electronic clock, stopwatch and other instruments to count even smaller durations of time.
• An odometer is a device used for indicating distance travelled by an automobile.
• The metric system or standard set of units was created by the French in 1790.
• A ruler or scale, used now a days to measure length was invented by a William Bedwell in 16th century.
• A standard metre rod made of an alloy of platinum and iridium is placed at the Bureau of weights and measures in Paris. National Physical Laboratory in Delhi has a copy of this metre rod.
• One kilogram is equal to the mass of a certain bar of platinum-iridium alloy that has been kept since 1889 at the International Bureau of Weights and Measures in Sèvres, France.