Estimation and Measurement

Learning Points

•Estimation as measurement•Need for Measurements with scales •Use of Standard Units of Length •Measurement of Length •Measurement of Temperature•Making Graphs (Separate PPP)

Why do we need to measure?

Trade and Industry requires measurements in Standard Units

Science and Technology requires for progress (i) measurements to be as precise as possible, and (ii) units to be defined as unambiguously as possible

Activity on Estimation

A

B

Which line is longer, A or B?

Ask each child. Record the data on the black board. Discuss the results. How can the matter be resolved?

Estimating the length of a room

Each person will estimate the length of the room, write it on a piece of paper and hand it over to the assigned person. A Table of observations to be prepared.

Skills to be Developed

1

2 3 46

5

A bent scale

1 2 3 4 5 6 7

A scale with non-uniform graduation

1 2 3 5 7 8 9

A scale with missing graduation

Spotting a Correct Scale

1 2 3 4 5 6 7

A Correct scale

A scale broken at the edges

1 2 3 4 5 6 7

•Using the scale properly

( )

•Reading the scale properly

1 2 3 4 5 6 7 8

The eye must be right above the mark to be read.

•Expressing the result with proper units

In India we use only metric units of length

Unit Symbol

kilometer km

metre m

centimeter cm

millimeter mm

Units of length and their symbols.

Remember that m is an international symbol of metre. It has nothing to do with any language. So, in Hindi, Bengali, Tamil, Urdu, or in any other language, it is written as m. For example, 20 metres is 20 m, whatever the language you speak or write in.

No. Name Length reported

1. Gulabo 1 m 18.7 cms

2. Sultana 125.3 cm

3. Shinu 1 m 27.75 cm

4. Johnny 1 m 21.1 cm

5. Dolly 121.2

6. Seema 129.4 cm.

7. Sandy 4 ft 2 in

Sample data for the length of a table

In the above Table, only Sultana and Johnny reported the results properly. Others:

•Gulabo wrote cms instead of cm ( )•Shinu wrote 1 m 27.75 cm, tried to read between the mm marks. Not to be done ( )• Dolly did not write any units ( )• Seema wrote cm., again wrong ( )• Sandy expressed the result in ft and in, not to be used in science ( )

Mercury Thread

Mercury Bulb

A clinical thermometer is marked from 35 C and 42 C.

(Based on: Wikipedia Commons, under Free GNU Documentation License.)

Precautions in the use of clinical thermometer

• Wash the thermometer in clean water.• Jerk the thermometer to bring the mercury thread below 36 °C.• While reading the temperature, do not hold the thermometer by the mercury bulb.• After use, wash the thermometer before storing.

35 36 37 38 39 40 41 42

C

35 36 37 38 39 40 41 42

C

Blow-up of the constriction

Eye must be right above the mark to be read.

The constriction does not allow the mercury column to fall by itself. Thermometer must be jerked to lower the mercury column.

-10

0

10

30

110

90

70

50

100

C

A laboratory thermometer can measure temperatures from -10 C to 110 C. Zero and 100 marks are shown in bold. 0 C is the temperature of melting ice and 100 C is the temperature of boiling water under certain conditions. A temperature of 110 C means the temperature of a body 10 degrees hotter than the boiling temperature of water. Similarly, a temperature of -10 C means the temperature of a body 10 degrees colder than the melting ice.

Precautions in using a laboratory thermometer.

•The thermometer should be immersed in the liquid. It should be vertical and should not touch sides and the bottom of the container.

To read the thermometer correctly the eye must be right above the mark to be read