What is the law of universal gravitation? Why is gravitational ...

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What is the law of universal gravitation? Why is gravitational attraction not the same everywhere on
  the surface of Earth? What will be an ideal response?

Question 2

Why does continental crust stand higher than oceanic crust? What will be an ideal response?

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Answer to Question 1

Isaac Newton said that the force of gravity (F) between two masses (m1 and m2) is directly
proportional to their masses and inversely proportional to the square of the distance between their
centers of mass. This means that an attractive force exists between any two objects and the magnitude
of that force varies, depending on the masses of the objects and the distance between their centers.
Gravitational attraction would be the same everywhere on Earth's surface if the planet were perfectly
spherical, homogeneous throughout, and not rotating. But none of these things is true.

Answer to Question 2

Continental crust is granitic with an overall density of 2.7 g/cm3, and oceanic crust is made of basalt
and gabbro with a density for 3.0 g/cm3. Continental crust is around 35 km thick, and in mountain
ranges, it's much thicker. Oceanic crust is only 5 to 10 km thick.