Length

Length

Information

• Mars Climate Orbiter send by NASA to study the Martian climate, atmosphere, and surface changes , on December 11, 1998 was lost as the spacecraft went into orbital insertion, due to ground-based computer software which produced output in non-SI units of pound-seconds instead of the metric units of newton-seconds (N×s) specified in the contract between NASA and Lockheed.

$125 millionRs 787 Crore

So Why this happened ?

• Different countries use different measurement

• Can any of you name some measurements?

Ancient Tamil Measures

• 10 koaN= 1 nuNNaNu• 10 nuNNaNU= 1 aNu(atom)• 8 aNu= 1 kathirtthugaL• 8 kathirtthugaL= 1 thusumbu• 8 thusumbu= 1 mayirnuni• 8 mayirnuni= 1 nuNmaNal• 8 nuNmaNal= 1 siRu-kadugu• 8 siRu-kadugu= 1 eL• 8 eL= 1 nel• 8 nel= 1 viral= 8^8 aNu(atom)= 1.9444 centimetre• 12 viral= 1 saaN= 100 immi= 23.3333 centimetre• 2 saaN= 1 muzham= 46.6666 centimetre• 2 muzham= 1 kajam• 4 muzham= 1 paagam• 625 paagam= 1 kaadham= 5000 saaN= 1166.66 metres= 1.167

kilometre

Ancient Greek Measures• Distance Measurements• 1 digit or daktylos - plural : daktyloi (19.3 mm)• 2 digits = 1 condylos• 4 digits = 1 palaiste• 8 digits = 1 dichas• 12 digits = 1 spithame• 16 digits = 1 pous or foot - plural podes (309 mm) (Variations such

as Ionic foot 296 mm to the Doric foot 326 mm)• 20 digits = 1 pygon (called “Remen” by the Egyptians)• 24 digits = 1 pechya or pechys (πεχυα) ( small cubit)• 40 digits = 1 bema• 72 digits = 4.5 feet = 1 xylon

• So are you not confused ??• Its no wonder our satellite fell• So scientists world over

thought of finding a solution to overcome these problems.

• In 1960 an International Committee established set of standards for this basic quantities which is called the SI system. SI system stands for the french name (Systeme International d’ Unites)

Learning Objectives

• Fundamental Units !• Defining Length !• Measuring Length !• Instruments Used !

FUNDAMENTAL UNITS• All the laws of physics are

expressed in terms of basic quantities that require clear definition. The three basic quantities of physics are length mass and time. All the other quantities are expressed in term in these three.

• The other four basics units are:

oTemperature measured in Kelvin

oCurrent measured in Ampere

oLuminous Intensity measured in Candela

oAmount of substance measured in Mole

What is length?

• Definition [SI] Length is defined as the distance

travelled by light in vaccum in 1/299792458 seconds.

• Basic unit: The basic unit of length is metre

How to measure length?

Can you name some length measuring instrument ?Instruments used to measure height of a person ?Distance from earth to sun and nearest star ?Diameter of an atom ?

Instruments used to find Length

• Lengths can be measured with a ruler to an accuracy of about 1mm.

• Some investigations may need a more accurate measurement of length, which can be achieved by using Vernier Calipers or a micrometer screw gauge.

Vernier Caliper

Vernier Caliper

• The calipers shown in the last slide use a vernier scale. The simplest type enables a length to be measured to 0.01 cm. It is a small sliding scale which is 9 mm long but divided into ten equal divisions so

1 vernier division = 9/10 mm = 0.9 mm = 0.09cm

Vernier Caliper

• One end of the length to be measured is made to coincide with the zero of the millimetre scale and the other end with the zero of the vernier scale.

• The length of the object in Figure 1.11b is between 1.3cm and 1.4cm.

• The reading to the second place is obtained by finding the vernier mark which is exactly opposite (or nearest to) a mark on millimetre scale.

Vernier Caliper

• In this case it is the 6th mark and the length is 1.36 cm, since

OA = OB – AB OA = (1.90 cm) – (6 vernier divisions) = (1.90 – 0.54)cm = 1.36 cm

Vernier Caliper

Vernier scales are also used on barometers, travelling microscopes and spectrometers.

Micrometer Screw Gauge

• This measures very small objects to 0.001 cm. One revolution of the drum opens the accurately flat, parallel jaws by one divisions on the shaft of the gauge; this is usually ½ mm, i.e. 0.05 cm.

• If the drum has a scale of 50 divisions round it, then the rotation of the drum by one division opens the jaws by 0.05/50 = 0.001 cm. A friction clutch ensures that the jaws exert the same force when the object is gripped.


The object shown in the next slide has a length of

2.5mm on the shaft scale + 33 divisions on the drum scale = 0.25 cm + 33(0.001) cm = 0.283 cm


Before making a measurement, check to ensure that the reading is zero when the jaws are closed. Otherwise the zero error must be allowed for when the reading is taken.


Amazing Facts on Length

• Distance of Earth to the boundary of universe is = 1.4 x 1026 metres

• Distance from sun to the nearest star is = 4 x 1016 metres

• Distance of light travels in a year = 9.46 x 1016 metres

• Radius of Earth = 6.37 x 106 metre• Length of a housefly = 5 x 10-3 metre• Size of a cell = 1 x 10-5 metre• Diameter of hydrogen = 10-10

• Diameter of proton = 10 -15

Question Time

Level 1

Question

1. How many millimetres are there in a) 1 cm =b) 4 cm =c) 0.5 cm =d) 6.7 cm =e) 1 m =

Duration for taking down the questions – 1 minutesDuration for writing the answers – 3 minutesDuration for decorating the paper – 2 minutes

MarksAnswers – 10 marksDecoration - 5 marksDiscipline – 5 marksCo-operation – 5 marks

10405671000

Question

1. What are these lengths in metres:a) 300 cm = 3.00b) 550 cm = 5.50c) 870 cm = 8.70d) 430 cm = 0.43e) 100 mm = 0.1



Questions

1. What are the readings in these vernier scales:



Level 2

Question

2. Write the following as powers of ten with one figure before the decimal point:

a) 100 000b) 3500c) 428 000 000d) 504 27 056


Duration for taking down the questions – 10 secondsDuration for writing the answers – 1 minuteDuration for decorating the paper – 15 seconds

Question

2. What are the readings in the micrometer screw gauge in the picture present in the book page 8: Marks

Answers – 10 marksDecoration - 5 marksDiscipline – 5 marksCo-operation – 5 marks


Question

1. Write out the following in full:a) 103 =b) 2x106 =c) 6.92x104 =d) 1.34x102 =e) 109 =



Thank You

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Length