Gravitation
- 2. Earth attracts everything towards it by an unseen force of attraction.This force of attraction is known as gravitation or gravitation pull. The gravitational constant, approximately 6.673×10−11 N·(m/kg)2
- 3. Every object in the universe attracts other object by a force of attraction, called gravitation, which is directly proportional to the product of masses of the objects and inversely proportional to the square of distance between them.This is called Law of Gravitation or Universal Law of Gravitation.
- 4. The force that binds us to the earth The motion of the moon around the earth The motion of planets around the sun & The tides due to the moon and the sun .
- 5. When an object falls from any height under the influence of gravitational force only, it is known as free fall. In the case of free fall no change of direction takes place but the magnitude of velocity changes because of acceleration. This acceleration acts because of the force of gravitation and is denoted by ‘g’.This is called acceleration due to gravity. Expression for acceleration due to gravitation ‘g’.
- 6. The acceleration due to gravity on the surface of the Moon is 1.62519(412) m/s2, about 16.6% that on Earth's surface
- 7. Mass is the measurement of inertia and inertia is the property of any object which opposes the change in state of the object. It is inertia because of which an object in rest has tendency to remain in rest and an object in motion has tendency to remain in motion. Inertia depends upon the mass of an object. Object having greater mass has greater inertia and vice versa. Mass of an object remains constant everywhere, i.e. mass will remain same whether that object is at the moon, at the earth or anywhere in the universe.
- 8. Earth attracts every object towards it.We know that force is the product of mass and acceleration due to gravity. This means, F = m X g -----------------------(i) The force by which earth attracts an object towards it is called the weight of the object, which is the product of mass (m) of the object and acceleration due to gravity (g). Weight is denoted by ‘W’. Therefore, by substituting in the expression ‘F = mg’ we get, W = m x g ------------------------------(ii) Since weight is the force which is acting vertically downwards, therefore, weight has both magnitude and direction and hence it is a vector quantity. Since the value of ‘g’ is always constant at a given place, Therefore, expression ‘W = m x g’ can be written as follows: W α m --------------------(iii) This means weight of any object is directly proportional to its mass, i.e. weight will increase with the increase of mass and decrease with decrease in mass. This is the cause that weight of any object is the measure of its mass.
- 9. Buoyancy is the upward force exerted by fluids over the surface are of contact of an object which is immersed in fluids. Buoyancy is also known as upward thrust.
- 10. When an object is immersed in water, it exerts pressure over water due to its weight. At the same time water also exerts upward thrust over the object. If the force exerted by the object is greater than the upward thrust or buoyancy by water, the object sinks in water otherwise it floats over water.
- 11. (a) Swimming in water:–Anyone can be able to swim in water because of upward thrust exerted by water. (b) Flying of bird or aero plane :–Since air is a fluid, thus it also exerts upward thrust over the object.Therefore, because of upward thrust of air a bird or aero plane can fly in air.
- 12. Density of the fluid Volume of the object
- 13. Mass per unit volume of an object is called density or mass density. Density is denoted by Greek letter rho (ρ). Density = mass/volume Where, m is mass of object andV is the volume of that object.
- 14. The SI unit of mass is kg and SI unit of volume is cubic meter. Therefore, by substituting the unit of mass and volume in the expression of density we get p=kg/m3
- 15. For convenience the density of water is expressed in comparison of water.Thus, when density of a substance is expressed in comparison with water, it is called relative density. Relative density = density of substance / density of water Relative density has no unit, because it is the ratio of similar quantity.
- 16. Archimedes’ Principle states that when an object is immersed fully or partially in a liquid, it experiences an upward force which is equal to the weight of liquid displaced by the object.
- 17. The students should be able to define gravitational force. The students should be able to define and explain universal law of gravitation. The students should be able to discuss about the importance of the universal law of gravitation. The students should be able to define free fall. The students should be able to calculate the value of g. The students should be able to differentiate between weight and mass. The students should be able to discuss why objects float or sink when placed on the surface of water. The students should be able to perform activities related to force of buoyancy.
- 18. Students have to follow the given task and after that they have to test their progress jut given after every task. And check their progress also by clicking the option given in each answer. And any answer goes wrong then repeat the task again. And solve questions again.
- 20. (a)The force of attraction between any two objects is proportional to the product of their masses and inversely proportional to the square of the distance between them. (b)The force of attraction between any two objects is proportional to the product of their distances and inversely proportional to the square of the masses between them. (c)The law applies to objects anywhere in the universe. (d) A & c
- 21. (a) zero (b) v (c) 2v (d) infinity
- 22. (a) 6.6734x10-11N m2/kg2 (b) 6.6734x10-10N m2/kg2 (c) 6.6734x10-11N m/kg2 (d) 6.6734x10-11N m2/kg
- 27. (a) The distance between them (b) The product of their masses (c) The sum of their masses (d) The gravitational constant
- 28. (a) 1.66 m/s2 (b) 16.6 m/s2 (c) 10 m/s2 (d) 0.166 m/s2
- 33. (a) Kg/m3 (b) Unit less (c) Depends on the density of the substance (d) Depend on the density of water
- 38. (a)Sinks (b)Rises (c)Floats (d) First floats and then sinks
- 43. (a).The force that binds us to the earth (b).The motion of the moon around the earth (c).The motion of planets around the sun & (d).all of the above are correct