how do we get the acceleration due to gravity as 9.8 m/s^-2.any formula , equation , or somethig? please tell?

Answer 1

it can be measured on earth.

Answer 2

Newton's gravitational force F = GmM/R^2 can be combined with the equation for weight W = mg to give us F = GmM/R^2 = mg = W; so that g = GM/R^2. G is a constant having the same value anywhere in the universe. M is Earth's mass and R is the distance between the center of Earth's mass and whatever mass, m, that's being weighed.

If you know G, M, and R, you can solve for g anywhere. Of course, the easiest way to find g is to simply weigh the mass m to find W and then solve g = W/m.

Also, you will encounter physics problems that will ask something like, "What will g be at twice the distance from Earth's center?" And that you find by g'/g = GM/(2R)^2//GM/R^2; so that g' = g[R^2/(4R^2)] = g/4. Thus at twice the distance g' will be 1/4 th whatever it was at R. We often say that g varies inversely as the square of the distance.

There are a lot more equations/relationships. For example, pitting centripetal/centrifugal force against the weight of a satellite will invoke g considerations. Or, if a man can jump 4 feet on Earth's surface, how high can he jump on the Moon? If you're taking HS physics, you'll get them all.

Answer 3

For a body of mass m on the surface of the Earth, its weight, mg, is equal to the gravitational force of attraction on it by the Earth.
=> mg = (GmM) / R^2
=> g = (GM) / R^2
where,
G = Universal gravitational constant = 6.673 x 10^(-11) Nm^2/(kg)^2
M = mass of Earth = 6 x (10)^(24) kg
R = radius of Earth = 6400 km
Putting these values of G, M and R in the above equation
=> g = 9.8 m/s^2.