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Chapter 1 Physical Quantities and Measurement Selina Concise for Class 7 Physics  Points to Remember The mass of a body is the quantity of matter contained in a body regardless of its volume or any force acting on it.  The weight of a body is the force with which every body is attracted towards its centre.  The unit of mass in S.I. system is kilogram (kg). Higher units of mass are quintal and metric tonne.  The weight of body changes with acceleration due to gravity.  Weight is zero at the centre of the earth.  Mass per unit volume of a substance is called density of the body.  The unit of density in S.I. system is kg m -3  and gcm -3  in C.G.S. system.  The density in S.I. system is 1000 × numerical value in C.G.S. system.  The density of liquids and gases decreases or increases with the rise or fall in temperature. The cycle of upward and downward movements of the fluid form currents in the medium which are known as convectio...

Chapter 2 Motion Selina Concise for Class 7 Physics  Points to Remember  Motion— Motion is the change in position with respect to a set of stationary landmarks.  Types of motion are translatory, rotatory and oscillatory.  A body is said to move in a translatory motion if the whole body moves through the same distance in the same interval of time.  A body is said to be in rotatory motion if it moves about a fixed point without changing the radius of its motion.  A body is said to be in oscillatory motion if it moves to and fro about its mean position.  A body is said to be in vibratory motion if the body moves to and fro in a particular style.  Oscillation of pendulum is one complete to and fro motion.  The maximum displacement on either side of a mean position is called amplitude.  A motion which repeats itself at regular intervals of time is called periodic motion.  A physical quantity which has only magnitude and no direction is c...