CBSE ADDA

Matter and Energy

Mass

Natural objects visible to us are made of different types of matter-solid, liquid or gas. The quantity of such matter that an object possesses is its mass. It is a physical quantity having magnitude only and no direction, so mass is a scalar quantity.

Weight

Every material particle on or near the earth is attracted towards the earth’s centre, called gravity. The weight of a body is the sum of all such pulls on all the particles the body is composed of. That is why a body composed of a larger number of particles i.e. a body of larger mass has greater weight than a body of smaller mass consisting of less number of particles.

Force is the product of mass and acceleration, also, weight of a body is a force, so, weight of a body = mass of the body x acceleration due to gravity.

Or, W = mg, where ‘W’ is the weight and ‘m’ is the mass of the body and ‘g’ is the acceleration due to gravity.

Therefore, weight is a vector quantity because it has magnitude and direction as well.

Mass is more fundamental than weight

Mass of a body is not affected due to motion or its position in different places on the earth and on different planets. It also remains unchanged in different conditions of heat, light, electric and magnetic fields. In a word, it is an intrinsic property of all material bodies. On the other hand weight of a body given by the equation W = mg as shown earlier changes with the variation of ‘g’. The value of ‘g’ changes (i) at the poles, equator or other places on the earth; (ii) at different altitudes; (iii) at different planets; (iv)due to earth diurnal motion. Thus a body’s weight is variable but not the mass.

Conservation of mass

In ordinary chemical or physical change, total mass of the substances before the change is equal to the total mass of the products after the change. Lavoisier first enunciated the law of conservation mass. Much before Lavoisier, ancient Indian philosophers enunciated the same as; ‘anything that exists is imperishable ’.

Energy

Energy of a body or system is a measure of its ability to do work. In this universe, energy exists in different forms – mechanical energy, light energy, electrical energy, sound energy, atomic energy, chemical energy etc.