MOTION AND MEASUREMENT OF DISTANCES | SPEED NOTES | SCIENCE | CBCE | CLASS 6

CBSE Class 06 Science Revision Notes CHAPTER – 10 Motion and Measurement of Distances REST : The objects whichremain stationary at a place and do notchange their position are said tobe at rest. Different modes oftransport are usedto go fromone place toanother. In ancient times, people used thelength of a foot, thewidth of a finger, thedistance of a step as units of measurement. This caused confusion and a need to develop auniform system ofmeasurement. we use International System of Unit ( SI unit). This is accepted all over the world. Meter isthe unit oflength in SIunit. Motion in astraight line iscalled rectilinear motion. In a circular motion, an object moves such thatits distance froma fixed point remains the same. Motion that repeats itself after someperiod of time, is called periodic motion. Measurement: The comparison of an unknown quantity with someknown quantity ofthe same kind. Measurement of anobject consists of: The unit of measurement. The number of units theobject measures. Conventional Methods of Measurement: Conventional measurements haveonly been approximate measurement. Differ fromperson to person. Lack precision.

Hand span:Lengthbetween the tipof the thumb and little finger. Cubit: Length between the tip of middle finger and elbow. Arm length: Length from shoulder to the tip of middle finger. Footstep: It is the distance covered by astep.

Needs forstandard units of measurement:- Units such ashand span, foot, footstep, cubit, etc., vary. they depend upon the sizeof an individual's hand,foot,etc., hence suchunits cause confusion in measurements. Standard Units of Measurement: It isa unit tomeasure any quantity completely and uniformly. Standard units for measuring, length-metre, mass-kilogram, time-second. 'The system International of 'Units' or better knownas 'S.I. UNITS.

RULES FORWRITING SYMBOLS OF UNITS Symbols for units are usually written in small letters. Symbols is not givenin plural form. Symbols for a unit isnot to befollowed by a full stopunless it isat the endof a sentence. Motion: When the position of a body does not change with the passage of time, the body is saidto be atrest. When theposition of abody changes withthe passage oftime, the bodyis said to bein motion. Types ofmotion: (a) Linear Motion: Linear motion is further classified into two: 1. Straight line motion or Rectilinear Motion: Object moves from oneposition to another along a straight line. Example: agroup of antsmoving in aline. 2. Curvilinear Motion: Object moving along curved lines. Example: a carmoving along a curved road. (b) Random Motion: When an object movesfrom one position to another andchanges direction inan irregular manner. Example: butterfly, flies randomly in thegarden. (c) Circular Motion: Object moves in a circular manner in relation to its ownaxis or around a fixed centre. An object remains at the samedistance from afixed point which is the centre of the pathof the motion. Two types ofcircular motion: (i) Revolution, taking rounds around: Object moves asa whole around a fixed centre.

Example: Earth revolving around the sunin a definite orbit. (ii) Rotation or spinning motion: Object moves in a circular path in relation to its ownfixed axis. Example: blades of a moving fan,windmill, etc. Rotation is restricted to the central axis. The extended parts attached to the rotating axis are in revolutionary motion. (d) Vibratory Motion: Object movesto and frovery fast. Example: strings of a guitar when plucked. (e) Oscillatory motion: Object oscillates to andfro along thesame path againand again andwith the samespeed. Time taken by an object to complete oneoscillation is same, no matter how many oscillations the object takes. Example: heartbeat, apendulum of aclock. (f) periodic motion: - The motion which repeats atregular intervals oftime is a periodic motion. Ex.heartbeat, pendulum oclock, hands ofa clock. (g) Non-periodic Motion: Object doesnot repeat motion at regular intervals of time.Ex. Earthquake, theeruption of a volcano, landslide, storm. (h) Mixed motion: - more thanone type ofmotion at thesame time. Ex.A cricket ball bowled shows linear as wellspin motion. (i) Resultant motion: - one kind ofmotion resulting in another kindof motion isa resultant motion. Ex. wheels ofa bicycle rotate about its axisresulting in thelinear motion ofthe bicycle on theroad. (j) Random motion: - The motion without any sequence or direction israndom motion. Ex. A buzzing bee, A player of a football on the field. (k) Uniform Motion: When thebody covers theequal distance inequal time interval.motion of aclock hand. (l) Non-uniform Motion: Motion inwhich the bodycovers the unequal distance in equal inter of time, themotion of a bus.