MOTION [CLASS -9]

QUANTITIES  UNITS  DISTANCE  DISPLACEMENT  SPEED  VELOCITY  ACCELERATION

 MOTION

CONTENTS

• Point of reference
• Origin


• State of rest


• State of motion


• Physical Quantities


• Units and System of units


• Scalar


• Vector


• S.I. units of physical quantities


• Distance


• Displacement


• Speed


• Velocity


• Acceleration


• Uniform Circular Motion


• Equations of motion


• Graphical representation of motion


• Position-time graph


• Velocity- time graph


• MCQ

1.POINT OF REFERENCE

It is the point using which the location of an object is expressed. A tree, building, tower, etc,any visible thing is taken as the point of reference.

2.ORIGIN

It is the point of reference . Generally, in coordinate geometry the point of intersection of mutually perpendicular x-axis and y- axis is called as origin.

3.STATE OF REST

If an object does not change its location(position) with respect to its point of reference with the passage of time then the object is said to be in the state of rest.

4.STATE OF MOTION

If an object changes its location(position) with respect to its point of reference with the passage of time then the object is said to be in the state of motion.

5.PHYSICAL QUANTITIES

Those quantities which can be measured and the laws or equations of Physics can be expressed in terms of these, are called physical quantities.
Examples:-
i)'Beauty' cannot be measured. So this is not a physical quantity.
ii)'Force', 'Speed', 'Acceleration' etc., can be measured. So these are physical quantities.
Main points relating to physical quantities:-

• We need numerical value(n) and a unit (u) to express a physical quantity(Q) completely.
  i.e, Q= nu
  
• Classification of physical quantities:-

1)Fundamental or Basic Physical Quantities:- These are 7 quantities.
i)Length ii) Mass iii)Time iv) Electric Current v) Thermodynamic Temperature
vi) Luminous Intensity vii) Amount of substance
2)Derived physical quantities:-These are derived from basic quantities by multiplication or division. Speed, Velocity, Acceleration, Force, Power, Energy etc.

6.UNITS AND SYSTEM OF UNITS

• UNIT :-To measure a physical quantity same type of quantity is assumed as standard. This standard quantity is called unit of that quantity. For example, to measure length,1 metre length is assumed as standard. So, 1 metre is the unit of length.
• SYSTEM OF UNITS:-
  a)F.P.S. System :-In this system, length, mass and time are measured by foot, pound and second respectively.
  b)C.G.S.System:-In this system, length, mass and time are measured by centimetre, gram and second respectively.
  c) M.K.S. System :-In this system, length, mass and time are measured by metre, kilogram and second respectively.
  d) S.I. System :- This is the extended version of M.K.S.System.The units of seven basic quantities are given in S.I. as below-
  

  S.N.	Basic quantities	S.I. Units	Symbol of units
  1.	Length	metre	m
  2.	Mass	kilogram	kg
  3.	Time	second	s
  4.	Electric current	Ampere	A
  5.	Temperature	Kelvin	K
  6.	luminous intensity	Candela	cd
  7.	Amount of substance	mole	mol

7.SCALARS

• Those physical quantities which have only magnitude and no direction, are called scalars.
• Examples :- length, distance, speed, volumw, mass, density, energy, work, power, wavelength, frequency, amplitude, loudness, intensity ,etc.
• scalars can be combined by using the laws of ordinary algebra.

8.VECTORS

• Those physical quantities which have magnitude as well as direction ,are called vectors or vector physical quantities.
• Examples :- displacement, velocity, acceleration, momentum, force etc.
• Vectors cannot be combined by using the laws of ordinary algebra.
• Vectors can be combined by using the laws of vector algebra.

9. S.I. UNITS OF PHYSICAL QUANTITIES

S.N.	Physical quantities	S.I. units	Brief of units	scalar/vector
1.	Distance	metre	m	scalar
2.	Displacement	metre	m	vector
3.	Speed	metre per second	ms-1	scalar
4.	Velocity	metre per second	ms-1	vector
5.	Acceleration	metre per second2	ms-2	vector

10. DISTANCE (s)

• Definition :-The measure of actual path covered by an object from initial position to final position is called distance.
• Distance is scalar :-Distance is described only by using magnitude of length with its proper unit, direction is not used. Hence distance is considered as a scalar.
• Distance depends on nature of path :-The value of distance depends on the nature of the concerned path means on the shape of the path. That's why, for two given points the values of distance are different for different paths.
• Sign of distance :-Distance is always expressed by positive values. Its values can't be negative.
• For two given points, zero distance is not possible:- Distance can't be zero. If initial position and final position both be coincident i.e. both be at the same point even though distance is not zero.
• S.I. unit of distance:- metre (m)
• Another units of distance:-(a)For large distance - Light year, parsec, kilometre, miles, Nautical mile, Yard (b) For small distance -inch, foot, centimetre, millimetre
  Light year and parsec are used to measure astronomical distances.
• Relations between units of distance:-
  (i)  1 light year = 9.461 x 10¹⁵ m
  (ii)  1 parsec = 3.26 light-years = 3.086 x 10¹⁶m
  (iii)  1 km = 1000m
  (iv)  1 mile = 1.609km = 1609.34m
  (v)  1 inch = 2.54cm = 0.0254m
  (vi)  1 foot = 12 inch =30.48 cm = 0.3048m
  (vii)  1m = 100cm
  (viii)  1 nautical mile = 1.852 km = 1852m
  (ix)  1 Yard = 0.9144m
  (x) 1cm = 10mm

11. DISPLACEMENT (s)

• Definition :-The minimum distance with direction from initial position to final position is called displacement.
• Displacement is vector :-Displacement is described by using magnitude of length with its proper unit as well as direction. Hence displacement is considered as a vector.
• Displacement doesn't depend on nature of path :-The magnitude of displacement depends only on the initial and final positions ,not on the nature of the concerned path means on the shape of the path. That's why, for two given points the magnitude of displacement is same for different paths.
• Sign of displacement :-Displacement may be positive or negative . Negative sign expresses opposite in direction . Positive sign expresses same in direction .
• Zero displacement is possible:- If initial position and final position both be coincident i.e. both be at the same point then displacement is zero in magnitude .
• S.I. unit of displacement:- metre (m)

12. SPEED (v)

• Definition :-
  The rate of change of distance with time is called speed.
  or, The magnitude of the change of position over time is called speed.
  or, The magnitude of the change of position per unit of time is called speed.
• Formula : speed = Distance/Time
• Speed is scalar :-Speed is described only by using magnitude with its proper unit and no direction. Hence speed is considered as a scalar.
• Sign of speed :-Speed is always positive.
• Average speed:- If the total covered distance be divided by the total time taken, then average speed is obtained.
• Instantaneous speed :-Speed at a particular instant of time is called instantaneous speed.
• uniform speed :-The motion in which equal distance is covered at each equal interval of time , is called in uniform speed.
• Non-uniform speed :-The motion in which unequal distance is covered at each equal interval of time , is called in non- uniform speed.
• Speedometer :-Speedometer measures instantaneous speed of a vehicle.
• S.I. unit of speed:- metre per second (m/s), ms^-1
• Relation between km/h and m/s
  

  km/h	m/s
  1km/h	5/18m/s
  18km/h	5m/s
  36km/h	10m/s
  54km/h	15m/s
  72km/h	20m/s
  90km/h	25m/s

13. VELOCITY (v)

• Definition :-
  The rate of change of displacement with time is called velocity.
  
• Formula : velocity = Displacement/Time
• Velocity is vector :-Velocity is described by using both magnitude with its proper unit as well as direction. Hence velocity is considered as a vector.
• Sign of velocity :-Velocity may be positive or negative.
• Average velocity:- If the total covered displacement be divided by the total time taken, then average velocity is obtained.
• Instantaneous velocity :-Velocity at a particular instant of time is called instantaneous velocity.
• uniform velocity :-The motion in which equal displacement is covered at each equal interval of time , is called in uniform velocity.
• Non-uniform velocity :-The motion in which unequal displacement is covered at each equal interval of time , is called in non- uniform velocity.
• Change of velocity :- Velocity may be changed due to the change in (a)its magnitude or,(b) its direction or (c) both magnitude and direction.
• S.I. unit of velocity:- metre per second (m/s), ms^-1

14. ACCELERATION (a)

• Definition :-
  The rate of change of velocity with time is called acceleration.
  
• Formula : acceleration = change in velocity/Time
• Acceleration is vector :-Acceleration is described by using both magnitude with its proper unit as well as direction. Hence acceleration is considered as a vector.
• Sign of acceleration :-acceleration may be positive or negative.
• Retardation:-The negative acceleration is called retardation.
• Average acceleration:- If the total change in velocity be divided by the total time taken, then average acceleration is obtained.
• Instantaneous acceleration :-Acceleration at a particular instant of time is called instantaneous acceleration.
• Uniform acceleration :-If the increasing in velocity,being moving along a straight line,be equal at each equal interval of time , then the object is said to be in uniform acceleration.
• Non-uniform acceleration :-If the increasing in velocity be not equal at every equal interval of time , then the object is said to be in non -uniform acceleration..
• Change of acceleration :- Acceleration may be changed due to the change in (a)its magnitude or,(b) its direction or (c) both magnitude and direction.
• S.I. unit of acceleration:-ms^-2

15. UNIFORM CIRCULAR MOTION

• Definition :-
  The motion of an object along a circular path with a uniform speed is called uniform circular motion.
  
• Constant speed:-In uniform circular motion speed of the object remains constant or uniform.
• Variable velocity:-In uniform circular motion velocity of the object remains variable due to change in direction at every point of the circle. Here, direction of velocity is tangential at each point of the circle.
• Centripetal acceleration :-Due to change in velocity in uniform circular motion, an acceleration produces radially towards the centre of the circle. This acceleration is called centripetal (centre searching ) acceleration. This acceleration is always normal to the direction of velocity at each point of the circle. It is given as ,
  a = v² / r
  Time period, T = 2πr / v
  Where r= radius of the circle,
  T = Time period = The time taken in one complete revolution
  v = uniform speed