Motion and Measurement of Distances, class 6, science

 

Motion and Measurement of Distances

 

• ·         In ancient times no means of transport were available people mainly travel by foot and carry luggage on their back
• ·         after domestication of animals human being start using horses, camels, elephants for transportation and carrying goods from one place to another
• ·         after inventions of steam engine as a new power source it lead to development of train, automobiles, motor ships as means of transport on water and land
• ·         after the invention electricity electric trains, aeroplane are used as new mode of transportation

 Measurement:

Measurement is the process of comparing the unknown quantity of an object to be measured with a standard unit of measurement

 ·         The quantities like length mass volume time speed and temperature can be measured are called physical quantities

• ·         In early Times people use parts of their body to measure the length of object

 

Conventional Methods: They give approximate measurement.

I.              Handspan: Length between the tip of the thumb and little finger

II.             Cubit: It is the length between the tip of the middle finger and elbow.

III.            Arm length: Length taken from shoulder to the tip of the middle finger.

IV.           Footstep: It is the distance covered in a step.

 

Disadvantages: Differed from person to person and lacked precision so this method is inaccurate.

Standard unit of measurement are those that have a fix quantity and their food do not very from person to person and place to place

 

Standard Units of Measurement: In 1960 scientist adopt uniform and conventional sets of standard unit for measuring physical quantities.

·         this system is known as international system of units or SI units

 

Some physical quantities are:

• ·         SI unit of length is metre (m)
• ·         SI unit of time is second (s)
• ·         SI unit of mass is kilogram (Kg)
• ·         SI unit of temperature is Kelvin (K)

 

Rules For Writing Symbols Of Units

1. Symbols for standard units are written in small letters.

 2. Symbols are not written in the plural.

 Metre: It is the standard unit of length. The symbol of metre is m.

Each metre (m) is divided into 100 equal divisions, called centimetre (cm). Each centimetre has ten equal divisions, called millimetre (mm). Thus
1 m = 100 cm
1 cm = 10 mm
For measuring large distances, metre is not a convenient unit. We define a larger unit of length. It is called kilometre (km).
1 km = 1000 m.

Sub-multiples of units: Units used for measuring smaller distances are the sub-multiples of SI units.
For example, milli, centi, deci.
1 m = 10 decimetre
1 m = 100 centimetre
1 m = 1000 millimetre.

Making measurement of a length: In making measurement of length of an object, we should follow the following procedure:
Place the scale in contact with the object along its length as shown in Fig.

Measurement with a scale with broken ends

·         Avoid taking measurements from zero mark.

·         Use any other full mark of the scale, say 1.0 cm.

·         Subtract the reading of this mark from the reading at the other end. For example, in Fig, the reading at starting mark is 1.0 cm and at the other end it is 5.5 cm. Therefore, the length of the object is (5.5 – 1.0) cm = 4.5 cm.

·        

 

Correct position of the eye is also important for making measurement. Your eye must be exactly above the point where the measurement is to be taken as shown in Fig. 10.4. Position ‘A’ is the correct position of the eye. Note that from position A’, the reading is 1.0 cm. From positions ‘B’ and ‘C’, the readings may be different.

Least count: A scale is marked in centimetres and millimetres. With the scales of this kind we can measure correctly up to one millimetre, that is one-tenth of a centimetre. This is called the least count of a (15 cm) scale.

 

Measurement Along Curved Line

Is it possible to measure a curved line with a metre scale? Well, it is not so. Hence to measure a curved line the following steps can be taken into account:

·      Take a thread and tie a knot at one end.

·      From this end measure a small portion of the curved line which is somewhat straight and put the thumb.

·      Now again start from the thumb marked position and measure another small portion of the line.

·      Repeat this process until you reach the end of the line. Tie a knot on the thread on reaching the end. Now measure the two knots using a metre scale.

 

Stationary objects: The object which do not move from its position is known as stationary objects

Rest: Object said to be at rest if it's position remain constant with respect to stationary object in the surrounding

 

Motion: An object is said to be in motion if it change its position with respect to stationery object in the surrounding

 

Rest and motion are relative terms for example and electric pole appears to be at rest or stationary when we observe it by standing on the road but the same pole appears to move when we observe from running train.

 

Types of motion: Types of motion for convention motion of different object can be classify as

 

1.    Translatory motion : when all the parts of the board object move the same distance in given time then the motion of an object is said to be translated  motion . for example

·         a child going down a slide

·         a vehicle moving on a road

 

Translatory motion  is are of two type: rectilinear motion and curvilinear motion

 (a)   Rectilinear motion:  when an object move along a straight line its motion is called rectangle motion. for example

·         a car moving in a straight line

·         ball falling from a roof

(b)  Curvilinear motion:  when an object move along a curved line called curvilinear  motion for example

·         a car moving along a curve path

·         a ball is thrown by a boy second

 

(2) Circular motion: when ana object moves along a circular path, it is said to be circular motion. For example

·         motion of the moon around the earth

·         running of athlete in a circular track

 

(3) Rotatory motion: object is said to be in rotatory motion if it moves about a fix Axis without changing its position. for example

 

·         the motion of laid of fan spinning wheel

·         merry go round

(4) Oscillatory motion: when and object move to-and-fro about its mean position, its motion is called oscillatory motion.for example

·         motion of swing

·         motion of pendulum

(5) Vibratory motion: a motion in which a part of object remain fixed and do not move while the other part of object move to-and-fro in a definite pattern is called vibratory motion for example

·         Guitar

·         drum

(6) Periodic motion: the motion that ready repeat itself after regular interval of time is called periodic motion for example

·         swinging pendulum of wall clock

·         needle of machine

·         heartbeat

·         motion of Earth

(7) Non- Periodic motion: the motion that does not repeat itself at regular interval is called Non- Periodic motion.

 

Note- Sometime a body can possess more than one types of motion at the same time such type of motion is called multiple motion. For example

·         a boy writing a bicycle here the wheels of the bicycle rotate and at same time it move in a straight path so it have rotatory and rectilinear motion

·         Earth rotate about the sun so it have circular motion as well as rotatory motion because it rotate about its axis.