Tanusri Gururaj, Academic content writer of Physics at Edumarz

It is due to the Earth’s gravitational force. 

SI unit of g = ms-2

  • Let the mass of an object be m. The gravitational force of this object will be equal to mg.

Hence, F = mg

But, we know that F = GMm/d2

Equating them we get,

mg = GMm/d2

Or g = GM/d2

M = mass of Earth

d = distance between object and Earth

If an object is on the surface of Earth or near it, we can take d = Radius of the earth (R).

Therefore, g = GM/R2.

  • Calculation of g:

Let us take the following values for calculation

M = 6 × 1024 kg

G = 6.67 x 10-11 N m2 Kg-2

R = 6.4 × 106 m

Putting the above values in the formula g = GM/R2 we get, 

g = 9.8 ms-2

  • Acceleration due to gravity or, ‘g’ is constant near the Earth and, therefore, in the equations of motion, ‘a’ can be replaced by ‘g.’

v = u + gt

s = ut +½ gt2

v2 – u2 = 2gs

Note: ‘a’ is taken positive when in direction of velocity. 

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