Laws of motion - Selina Concise Chemistry Solutions Class 10 Chapter 10 Study of Compounds Nitric PDF

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Selina Concise Chemistry Solutions Class 10 Chapter 10 Study of Compounds Nitric Acid...

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9 ICSE :-

Chapter -3 Laws of Motion (Part-4)

Universal Law of Gravitation According to Newton, the force of attraction acting between two bodies is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. F = Gm1m2/r2 F = force of attraction, r = distance between two masses m 1 and m2 G = universal gravitational constant. Value of G = 6.67 x 10 -11 Nm2/kg2 Unit of G - Nm2/kg2 Gravitational constant G is numerically equal to the magnitude of force of attraction between two masses each of 1 kg placed at a separation of 1 m. Gravitational force between two masses (i) is always attractive. (ii) is directly proportional to the product of the masses. (iii)

is inversely proportional to the square of separation between them. (iv) is significant between heavenly bodies, but is insignificant between ordinary bodies because of small magnitude of G. Importance of the universal law of gravitation By applying this law one can explain the motion of planets around the sun, the motion of the moon (satellite) around the earth and the motion of a freely falling body. Force due to gravity The force with which the earth attracts a body, towards its centre is called force of gravity. F = GMm/R2 The earth attracts a body of mass 1 kg by a force of 9.8 N towards its centre.

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Acceleration due to gravity (g) The acceleration produced in a freely falling body due to the gravitational force of attraction of earth. Unit is m/s2. Value of g on the surface of earth =9.8 m/s2. It is a vector quantity directed vertically downwards towards the centre of earth. On the Earth’s surface, the value of g varies from place to place. The value of g is zero at the centre of earth. At altitudes above the earth’s surface or at depth below the earth surface, the value of g decreases. On equator, it is slightly less as compared to that at poles. Relationship between g and G g = GM/R2 g = acceleration due to gravity, G = gravitational constant, M = mass of planets or satellites, R = distance between the bodies. The value of g on a planet or satellite depends on the mass and radius of that planet or satellite. Free fall Equations of motions for a freely falling body :- 1.When a body is freely falling from a height v = u + gt h = ut + 1/2gt2 v2 = u2 + 2gh h = height through which the body falls, u = initial velocity, v = final velocity 2.When a body is thrown vertically upwards (g = negative) v = u - gt h = ut - 1/2gt2 v2 = u2- 2gh 3.When a body reaches the highest point then v = 0 u = gt u2 = 2gh hmax = u2/ 2gh Difference 2

between Mass and Weight. Mass

Weight

1.It is the measure of the quantity of matter contained in the body.

1.It is the force with which a body is attracted towards the centre of Earth.

2.Scalar quantity.

2. Vector quantity.

3.S.I unit is kg.

3. S.I unit is newton (N).

4.Measured using physical balance.

4. Measured using spring balance.

5.Variable quantity, varies 5.It is constant for a from place to place due to body and does not change in the value of g. change with the change in place. Gravitational units of Force 1.One kilogram force –1 kgf is the force due to gravity on a mass of 1 kg. 1 kgf = 9.8 N 2 . One gram force – 1 gf is the force due to gravity on a mass of 1 g. 1 gf = 980 dyne. ****************************

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