1. Mass of an object is the measure of its inertia. Greater the mass, the greater is the inertia. It remains the same whether the object is on the earth, the moon or even in outer space. The usual symbol for mass is m and its SI unit is the kilogram. Gravitation Mass

2. Weight (W) is the gravitational force acting on an object. Gravitational force depends on the mass (m) of the object and the acceleration due to the gravity (g). W = m × g Gravitation Weight

3. Weight has both magnitude and direction. The SI unit of weight is, newton (N). Weight of a body vary place to place and become zero on the center of earth and far away from the surface of earth. Gravitation Mass and Weight

4. MassWeight (1) The quantity of matter in a body is called its mass. (1) Weight is the force by which the earth attracts a body towards its center. (2) Mass is a scalar quantity.(2) Weight is a vector quantity and is always directed towards the center of the earth. (3) Mass of a body is always constant every where in the universe. (3) Weight of a body vary place to place and become zero on the center of earth and far away from the surface of earth. (4) Unit of mass in S.I system is KILOGRAM ( kg). (4) Unit of weight in S.I system is NEWTON (N). Gravitation Difference between Mass and Weight

5. Suppose a body of mass m and its weight on the moon is W m. Mass of the moon is M and its radius is R. Weight of an object on the moon = F (Force)with which the moon pulls. Gravitation W m = GM × m/R 2 Weight of the same object on the earth is We. Mass of the earth is 100 times of that of the moon. ( By universal law of gravitation) Radius of the moon = R Weight of an object on the Moon

6. W m /W e = 16/100 =1/6 Weight on the moon is 1/6 weight on the earth. Gravitation Weight of an object on the Moon Radius of the Earth = 4R Weight of the object on the earth, W e = G100M × m/(4R) 2 W e = G100M × m/(16R) 2

7. An object weighs 20 N when measured on the surface of the earth.What would be its weight when measured on the surface of the moon? Thus, the weight of object on the surface of the moon would be 3.34 N. Gravitation Weight of an object on the Moon Example Solution We know, Weight of object on the moon = (1/6) × its weight on the earth. That is,