1. What is difference between gravitation and gravity? Gravitation is the force of attraction betw3een any two bodies in the universe while gravity refers to the force of attraction between any body and the earth. Clearly, gravity is the special case of gravitation. Which one is greater- the attraction of the earth of 1 kg o lead or the attraction of 1 kg of lead on the earth? The force of attraction between two bodies is given by F= Gm1m2/d2. In this case F= G(1*m2)/d2 where m2 = mass of the earth. So the force of attraction of the earth on 1kg of lead will be the same as that of 1 kg lead on the earth. 2.Why does the earth impart to all bodies the same acceleration irrespective of their masses? Is it true for other forces, the pull of engine on a train, for example? We can write F=GmM/R2 = mg Or, g = GM/R2 = a constant. This relation shows that acceleration due to gravity on all bodies is the samw irrespective o their masses. Bo, it is not true for other forces. For the pull of an engine F=ma⇒a =F/m i.e. the acceleration is inversely proportional to the mass. 3. Why G is called universal gravitational constant? This is because the value of G is same whatever is the nature of the medium between any two bodies or whatever the nature of the bodies themselves is. 4. Earth is continuously pulling the moon towards its centre, still it does not fall to the earth .Why? Gravitational force of attraction due to earth provides the centripetal force, which keeps the moon in orbit around the earth. 5. The mass of the moon is nearly 10% of the mass of the earth. What will be the gravitational force of the earth on the moon, in comparison to the gravitational force of the moon on the earth? Both forces will be equal in magnitude because gravitational force between two bodies is a mutual force. 6. What is more fundamental mass or weight? Mass is more fundamental because the mass of a body remains constant. However, the weight (=mg) of a body change due to the change in the value of g. 7. If gold were sold by weight, would you rather buy it in Kathmandu valley or in Janakpur of Nepal? If it were sold by mass, in which of the two locations would you prefer to buy it? Why? Kathmandu is at higher place in comparison to Janakpur so acceleration due to gravity is less in Kathmandu and therefore the weight of gold will be more in Janakpur and obviously, we prefer to buy gold by weight in Janakpur. The mass is independent of place so whether we buy gold by mass in Kathmandu valley or Janakpur, its value will be the same. 8. Difference between mass and weight. MASS WEIGHT 1. It is the property due to matter contained in a body. 2. It does not change with space. 3. It can never be zero. 4. It is a scalar. 5. It is measured in kilogram. 1. It is the property of a body developed due to acceleration due to gravity. 2. It changes from place to place. 3. It may be zero. 4. It is a vector. 5. It is measured in Newton. 9.Where will a lady weigh more -1km above the surface of earth or 1Km below the surface of earth? The acceleration due to gravity (g) is given by .. g1 = (1- -h/R) above the earth’s surface. …g2 = (1--2h/R) below earth’s surface. These relations tells us that g2>g1 so the body will weigh more at a depth of 1km below the surface of earth. 10.What will be our weight at the center of earth, if the earth were a hollow sphere? The acceleration due to gravity is g1 = (1- -h/R) below earth’s surface. At the center of the earth h=R so g’ = 0. So our weight = mg’ =mx0=0. A body of mass 5Kg is taken to the centre of the earth. What will be its mass there? Mass of the body will remain 5kg at the centre of the earth because mass of a body does not depend on place. 11.Why does a tennis ball bounce higher on a hill than on planes? The value of g is less on hills because they are comparatively at a greater distance from the centre of the earth. Therefore, the gravitational pull on the tennis ball is less on hill tops and so it bounces higher on hills than on planes Great, sir 12. Why do you feel giddy (dizziness) while moving on a merry-go-round? When moving in a merry-go-round, our weight appears to decrease when we move down and appear to increase when we move we move up. Due to increase and decrease in eight during moving a merry-go=round, we feel giddy. 13. When dropped from the same height a body reaches the ground quicker at poles than at the equator. Why? The acceleration due to gravity is more at the poles than at the equator. When the initial velocities and distances travelled are the same, the time taken by the body is smaller if the acceleration due to gravity is large. Hence, when dropped from the same height, a body reaches the ground quicker at the poles than at the equator. 14. What is the effect on our weight due to revolution of the earth about the sun? There is no any factor involved in the expression of g which is influenced by the revolution of the earth about the sun so we can say that no effect is on our weight due to revolution of the earth about the sun. 15.What would happen if gravity suddenly disappears? If gravity suddenly disappears then, a) All bodies will have zero weight. b) Human beings will be thrown out of the surface of the earth due to centrifugal force. c) Motion of all satellites around the earth is not possible as the centripetal force ceased in absence of gravitational force.
Posted on: Sat, 20 Dec 2014 10:43:07 +0000
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