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Scalars and Vector Quantities Scalar Quantities: The physical quantities which are specified with the magnitude or size alone are scalar quantities. For example,  length, speed, work, mass, density, etc. Vector Quantities: Vector quantities refer to the physical quantities characterized by the presence of both magnitude as well as direction. For example, displacement, force, torque, momentum, acceleration, velocity, etc. Comparison between Scalars and Vectors Criteria Scalar Vector Definition A scalar is a quantity with magnitude only. A vector is a quantity with the magnitude as well as direction. Direction No direction Yes there is the direction Specified by A number (Magnitude) and a Unit A number (magnitude), direction and a unit. Represented by Quantity symbol Quantity symbol in bold or an arrow sign above Example Mass and Temperature Velocity and Acceleration Characteristics of Vectors The characteristics of vectors are as followed

Unit and Dimensions The comparison of any physical quantity with its standard unit is called measurement. Physical Quantities All the quantities in terms of which laws of physics are described, and whose measurement is necessary are called physical quantities. Units A definite amount of a physical quantity is taken as its standard unit. The standard unit should be easily reproducible, internationally accepted. Fundamental Units Those physical quantities which are independent to each other are called fundamental quantities and their units are called fundamental units. S.No. Fundamental Quantities Fundamental Units  Symbol 1. Length metre m 2. Mass kilogram kg 3. Time second S 4. Temperature kelvin kg 5 Electric current ampere A 6 Luminous intensity candela cd 7 Amount of substance mole mol Supplementary Fundamental Units Radian and steradian are two supplementary fundamental units. It measures plane angle and solid angle respectively. S.No. Supplementar

SOUND Main topics covered in this part of CBSE Class 9 Science, Sound: Chapter Notes, are: Sound-Production and Propagation Medium Wave and its Types Characteristics of Sound Audible Frequency Reflection of Sound and its Laws Applications of Reflection of Sound Sound Sound is a form of energy which produces a sensation of hearing in our ears. Production of Sound Sound is produced due to the vibration of objects. Vibration is a periodic back-and-forth motion of the particles of an elastic body or mediumkind about a central position. It is also named as oscillation. For example: Stretched strings of a guitar vibrate to produce sound. When membrane of a table is struck, it vibrates to produce sound. Propagation of Sound The travelling of sound is called propagation of sound. Sound is propagated by the to and fro motion of particles of the medium. When an object vibrates, the particles around the medium vibrate. The particle in contact with the vi

WORK, ENERGY AND POWER  Whenever a force makes a body move, then work is said to be done. But for doing work, energy is required. When work is done by human beings, machines or animals they get energy from the food which they eat and if work is done via machines, then energy is supplied by fuels or by electricity. So, we can say that when work is done an equal amount of energy is used up. Work Work can be done when a force produces a motion. For e.g . when a person climbs the stairs of an office or a house, work is said to be done as he is moving against the force of gravity. Basically, Work done by a force depends upon two factors: (i) Magnitude of the force (ii) Distance through which the body moves in the direction of force. Therefore, Work is measured by the product of force and displacement of the body along the direction of force. It is a scalar quantity and its SI unit is joule. Work = Force X Distance (S) moved in the direction of force Or