IMPORTANTIMPORTANT NOTES NOTES IMPORTANT NOTES
7. Acceleration due to gravity of the Earth : The acceleration with which the bodies fall towards the earth is called acceleration due to gravity. Its average value is 9.81 ms–2. 8. Variation of acceleration due to gravity. (i) Acceleration due to gravity changes with the change in distance from the centre of the earth. (ii) Acceleration due to gravity is maximum at the poles of the earth. Its value decreases as we move towards the equator, such that its magnitude is least at the equator. (iii) Acceleration due to gravity decreases as we move inside the earth, such as deep mines. (iv) Acceleration due to gravity decreases as we move away from the surface of the earth, such as on the mountains, in aeroplanes, in spaceships, etc. 9. Mass : The amount of matter contained in a body is called mass. It is a scalar quantity and is measured by a physical balance. It is always a constant quantity and its unit in SI system is kilogram. 10. Weight : The force with which a body is attracted towards the centre of the Earth is called weight.
I. VERY SHORT ANSWER QuESTIONS
Assignments for summAtive Assessment
7. Why are sleepers used below the rails? [2010 (T-I)] 8. The gravitational force between two objects is F. How will the force change when the distance between them is reduced to 1/4 th? [2010 (T-I)] 9. What is meant by buoyant force? [2010 (T-I)] 10. A body of weight 20 N floats half submerged in a liquid. What is the buoyant force on the body? [2010 (T-I)] 1
1. State a relation between thrust and pressure. [2010 (T-I)] 2. State any one phenomena related to the Universal Law of Gravitation. [2010 (T-I)] 3. State Archimedes principle. [2010 (T-I)] 4. State universal law of gravitation. [2010 (T-I)] 5. State two factors in which the gravitational force between two objects depends. [2010 (T-I)] 6. What is the gravitational force between the Earth and a body called? [2010 (T-I)]
1. Force of gravitation : The force of attraction which exists between all objects, big or small, not only on the surface of the earth, but anywhere and everywhere in the universe, irrespective of the distances separating them, is called force of gravitation. 2. Newton’s law of gravitation : Every body in this universe attracts every other body with a force, which is directly proportional to the product of their masses and inversely proportional to the square of distance between their centres. 3. Gravitational constant : It is equal to the force of attraction between two unit masses, when they are separated by a unit distance, as measured from their centres. 4. SI unit of gravitational constant : The SI unit of gravitational constant is Nm2/kg2 or Nm2kg–2. Its value is 6.67 × 10–11 Nm2/kg2. 5. Force of gravity : It is a special case of force of gravitation, when one amongst the two bodies has an infinitely large mass as compared to the other body. 6. Force of gravity of the earth : The force of gravitation acting on the bodies close to the surface of the earth is called force of gravity of the earth.
PREVIOuS YEARS’ QuESTIONS
11. The G. Force between two objects is F. How will this force change when the distance between them is reduced to half? [2010 (T-I)] 12. Define mass of an object? [2010 (T-I)] 13. Why is G called the Universal Constant? [2010 (T-I)] 14. What is meant by free fall? [2010 (T-I)] 15. The Earth is acted upon by the gravitational force of attraction due to the Sun. Then why does the Earth not fall towards the Sun? [2010 (T-I)]
16. Two objects of masses M1 and M2 are dropped in vacuum from a height above the surface of Earth (M1 is grater than M2). Which one will reach the ground first and why? [2010 (T-I)] 17. An object of mass 2 kg falls with an acceleration of 9.8 m/s2 towards the ground. With what acceleration...