What does the assumption that grvitational potential at the surface of the earth is zero means?

Question

if the assumption is that gravitational potential at the surface of the earth to be zero, can we use the equation F=GMm/(r)^2?? Whats the meaning of the assumption? we use Energy=mgh instead??? Eg A mass of 2kg is at poiunt p, a height 3m above the surface of earth, to find the gravitational field strength at p what do we do?????????

Answer 1

It really doesn't matter how you define the gravitational potential-- you can put the zero wherever you want. For two reasons:

The equation for the force due to gravity isn't directly related to the gravitational potential, but you should be able to calculate it from the gradient of the potential. Adding a constant won't change the gradient, because the derivative of a constant is simply zero.

If you're using potentials to calculate energy conservation, you are only interested in differences between energies at different points. Adding a constant to each point doesn't effect the difference between the energies at different points. As long as you're consistent, you can assign the potential to be zero at wherever is convenient for you.

For your second question, to find the gravitational field strength at point p, assume the radius of the earth is constant, and the earth and the mass are point masses at the centers of the respective masses. Find the distance between the two centers, and then you can use GM(earth)/r^2 where G is the gravitational constant, M(earth) is the mass of the earth, and r^2 is the distance between the center of the earth and the center of the mass.

Answer 2

Your question is good in its own nature but your equation is a little off. It seems a little confusing the way you are asking it. However to accurately measure the strength of a field has not been completely invented. I mean they do have three detectors known on earth that can detect the gravitational waves that discern moving matter and those are LIGO and VIRGO the third I cant remember. But to my own theory is that there are two known gravitational pulls between out plant. The first is from the center of the earth where the iron core is spinning. The second is at the outer point of our atmosphere where the pressure from the earths air and the vacuum of space meets. It is directed by the magnetic pull from the sun. But between that range is no field generated actually what exists is the built up pressure of resistance that is between them which is known as your gravitational potential or gravity. So basically change the balance of the two fields and you change your potential.

Answer 3

the gravitational potential at the CENTRE of the earth is zero, at the surface of the earth I don't know the exact measurments but from memory it is 9.81 m/s^2.

Set your zero at the centre of the earth and your mathematics will work better

the gravitational force of an object is derived from a constant, multiplied by the mass of the object and divided by the radius squared. g~Km/r^2

at first glance this implies gravity approaches infinity at the centre of an object, but the reverse is true, as the mass from the other side cancels the gravity, at the centre the gravity is zero

hopefully a real scientist can explain it better than that

Answer 4

gravity is defined in physics as the force that pulls all objects on Earth towards the center of the planet...at the surface the "normal force" reacts in opposite direction of gravity so that there is a gravity effect of "zero" and only static friction is the force occuring on this object (if the object is understood to be at rest!)...the "normal force" counteracts gravity on Earth at the surface for the most obvious reason that Newton described as an object would be pulled thru the planet to the core!

Answer 5

I think we are on the same page. It is assumed that you are not going to fall to the center of the Earth while on the surface. Providing you do not fall into a manhole or other open pits, caves, or volcanoes.

Zero rest on the surface and that is what is assumed. No acceleration.

Here are some formulas:

Answer 6

You need to define gravitational potential.