How can the gravity be a constant if that of the earth is, say, six times weaker of the moon? Or inversely, how can be six time weaker than the earth when it is a constant?

That constant only holds here on earth. On the moon it’s like one sixth of that.

But a constant is…like…a constant.

I think you are also confusing acceleration due to gravity (g)with the universal gravity constant (G).

What you have written (incorrectly) in the details of your question is the “Universal Gravitational Constant”:
G = 6.674*10^(−11) N-m^2 / kg^2
(The carets – ^ – represent exponents in plain text writing.)

As @ARE_you_kidding_me notes, this is not the acceleration due to gravity, which will vary from place to place in the universe, as you can see here

In the sense that the acceleration due to gravity holds true for “planet Earth” or “the Moon” or some other celestial body, it is “constant for that place”. (Relatively, anyway. Gravity does actually differ slightly at different parts of the planet because of local masses.)

Think about it like this. If you put a few items in a salad spinner and turn it slowly the items might move a little to the edges. If you spin it fast, the items will stick to the sides on the spinner. The gravitational force increases with the faster spin. Each planet and moon has it’s own set of variables that creates the different gravitational pulls.

The stuff the moon is made of has the same gravitational effect as the stuff the Earth is made of but there is six times more Earth stuff than moon stuff.

@JLeslie that’s the centripedal force not gravity. It can be used to simulate gravity on the inside edge of a rotating body though

That is centripetal

The “gravitaty constant” is not the same as gravity, which we experience as an acceleration toward the ground. Rather, it is a constant of proportionality between the gravitational force between two objects and the product of their masses divided by the square of the distance between them. That is, the force of attraction between two objects is proportional to the product of their masses divided by distance squared; to get the exact value of the force, you have to multiply this quantity by a constant – specifically, the universal gravitational constant you mentioned.

The equation for Newton’s law of gravitational attraction between two objects is

F = G*m1*m2/r^2

where G is the gravitational constant, m1 and m2 are the masses of the objects and r is the distance between the masses. This force is fundamental and holds for all pairs of objects in the universe.

The force of attraction between two objects is always dependent on the masses of the objects and the distance between them. But no matter which two objects or what distance you are considering, the gravitational attraction between them will always be a multiple of G.

Mass effects gravity. It’s right there in the equation. If you understood the equations you were (trying to) write, you would understand how you can’t expect gravity on earth to be the same on the Earth as it is on the moon. Go back and do some more reading. Curiosity about the subject is half the battle.

Try ‘Seven brief lessons on physics’ by Carlo Rovelli It might help.

Gravity is a constant ~in relation~ to the mass of the object providing the gravitational pull. The larger the mass, the stronger the pull.

That doesn’t mean size. If object A weighs 124568426965729359lbs, but is only 2ft tall, it will have a stronger pull than object B weighing 129lbs and 23487650761ft tall.

The gravitational attractive force between two objects is F = G * m1 *m2/ (r*r). G is the constant. m1 and m2 are the masses of the two objects. r is the distance between their centers of mass. The more mass of one and/or mass of the other, the more gravitational force.

You are thinking of you vs Earth, compared with you vs Moon. Since the Moon has a lot less mass than Earth, you will feel less attraction on the Moon. Also you have to take into account the difference in diameters, to plug into the equation.

It ain’t the gravity that is constant. Gravity varies with masses and the distance between them. Its the universal gravitational constant G that is constant (duh!).
In simple terms Universal Gravitational Constant is the gravitational force between two masses of a kilogram each kept at a distance of one meter.
That, my buddy, is constant whether on moon or earth or your nearest subway, and that’s the bottomline ‘cause Joell said so! ;)
Feel free to ask more!

Gravity is different for all objects depending on the mass of the object. The earth is six times more massive than the moon. If the earth were crushed to the size of a basketball it would still have the same mass and be six times more massive than the moon. The same holds true with stars. White dwarfs are earth size. Neutron stars are city size but their mass is not relegated to the size difference. Neutron stars are many times more massive than white dwarfs.

Maximum Mass for White Dwarf: Mch = 1.4 Msun
First calculated by Subrahmanyan Chandrasekhar in the 1930s.
Above this mass, electron degeneracy pressure fails & the star collapses.

Mass of a Neutron Star
Mass ~1.2 – 2 Msun (???)
Radius ~10 km
Density ~1014 g/cc
Escape Speed: 0.70 c (70% speed of light)