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.