A change in density would not change the gravity of a body.
A Change in Earth's Gravity?
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A change in density would not change the gravity of a body.
danshawen
Valued Senior Member
???
Density = mass/volume
Fg = G(m1m2)/r1^2;
Fg = force due to gravity, G = universal gravitational constant, m1 = mass near surface, m2 = mass of planet, r1 = initial radius of planet
Assuming the density changed by means of changing the volume of a fixed mass, orbits far from the surface will not change very much, but shrinking the radius to accommodate a change in volume would alter surface gravity:
Fg/m1 = (G*m2) / r2^2; r2 = 0.5 r1; r2 = radius of shrunken planet
If the radius is shrunk to 1/2 r1 with the mass of the body held constant, the acceleration due to gravity increases by a factor of 4 at the surface.
Last edited:
comical
Technically speaking, he is correct - gravity is a function of mass, not density. The effect gravity has on an object DOES change with distance, but that is not what Origin is debating. Specifically, a change in the density of an object, without altering its mass, would not change its gravitational effect.
" The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume. The symbol most often used for density is ρ (the lower case Greek letter rho). Mathematically, density is defined as mass divided by volume: p= m/v "
" In physics, mass is a property of a physical body which determines the body's resistance to being accelerated by a force and the strength of its mutual gravitational attraction with other bodies....Thus, any stationary body having mass has an equivalent amount of energy, and all forms of energy resist acceleration by a force and have gravitational attraction. "
" Newton's law of universal gravitation postulates that the gravitational force of two bodies of mass is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. "
gravitation-
2. force that attracts things: the mutual force of attraction between all particles or bodies that have mass
mass-
5. physics: physical quantity: the property of an object that is a measure of its inertia, the amount of matter it contains, and its influence in a gravitational field.
density-
2. physics: relative mass: a measure of a quantity such as mass or electric charge per unit volume
then there is,
density function
" In physics, mass is a property of a physical body which determines the body's resistance to being accelerated by a force and the strength of its mutual gravitational attraction with other bodies....Thus, any stationary body having mass has an equivalent amount of energy, and all forms of energy resist acceleration by a force and have gravitational attraction. "
" Newton's law of universal gravitation postulates that the gravitational force of two bodies of mass is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. "
gravitation-
2. force that attracts things: the mutual force of attraction between all particles or bodies that have mass
mass-
5. physics: physical quantity: the property of an object that is a measure of its inertia, the amount of matter it contains, and its influence in a gravitational field.
density-
2. physics: relative mass: a measure of a quantity such as mass or electric charge per unit volume
then there is,
density function
" The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume. The symbol most often used for density is ρ (the lower case Greek letter rho). Mathematically, density is defined as mass divided by volume: p= m/v "
" In physics, mass is a property of a physical body which determines the body's resistance to being accelerated by a force and the strength of its mutual gravitational attraction with other bodies....Thus, any stationary body having mass has an equivalent amount of energy, and all forms of energy resist acceleration by a force and have gravitational attraction. "
" Newton's law of universal gravitation postulates that the gravitational force of two bodies of mass is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. "
gravitation-
2. force that attracts things: the mutual force of attraction between all particles or bodies that have mass
mass-
5. physics: physical quantity: the property of an object that is a measure of its inertia, the amount of matter it contains, and its influence in a gravitational field.
density-
2. physics: relative mass: a measure of a quantity such as mass or electric charge per unit volume
then there is,
density function
" In physics, mass is a property of a physical body which determines the body's resistance to being accelerated by a force and the strength of its mutual gravitational attraction with other bodies....Thus, any stationary body having mass has an equivalent amount of energy, and all forms of energy resist acceleration by a force and have gravitational attraction. "
" Newton's law of universal gravitation postulates that the gravitational force of two bodies of mass is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. "
gravitation-
2. force that attracts things: the mutual force of attraction between all particles or bodies that have mass
mass-
5. physics: physical quantity: the property of an object that is a measure of its inertia, the amount of matter it contains, and its influence in a gravitational field.
density-
2. physics: relative mass: a measure of a quantity such as mass or electric charge per unit volume
then there is,
density function
What you said is correct. Changing the density will not change the gravity of an object but if you were to move closer to the center of mass, such as staying on the surface that is closer to the center of mass you would definitely have a higher acceleration due to gravity. Still the gravity of the mass would not change.
I am curious too. He seems to think increasing the density of a mass increases the gravity (comical?) yet as far as I can tell he wrote nothing in support of that incorrect notion.:shrug:
sculptor
Valued Senior Member
gravity is a constantly moving/changing beasty
we have the earth's gravity, modified by ice and mountain building, modified by the earth moon system, modified by the other planets, and modified by the sun, then modified by our position on our arm of the galaxy
here's another pix of the anomalies on earth:
we have the earth's gravity, modified by ice and mountain building, modified by the earth moon system, modified by the other planets, and modified by the sun, then modified by our position on our arm of the galaxy
here's another pix of the anomalies on earth:
zgmc
Registered Senior Member
No one knows? well if anyone figures this out, I am also curious what the effect of gravity would be if you were the same distance from the center of the planet as we are currently.
Janus58
Valued Senior Member
With the same mass and half the radius, the Earth's surface gravity would be 4 times stronger. If you move out to a distance equal to that of its present radius, the gravity at that point would be equal to the Earth's present surface gravity.
zgmc
Registered Senior Member
Based on that, it seems that the gravity of a body really isnt "changed" by becoming more dense. The surface of the body is just closer to the gravitational center which leads to an increase of gravity on the surface.
Janus58
Valued Senior Member
Correct.
Someone already has mentioned a BH.
Let's Imagine that our Sun suddenly and magically became a BH.
That would mean squeezing the entire volume of the Sun, into about 5Kms diameter.
Gravity would not change, and all the Planets would go on orbiting as they presently do.
The only thing that really changes, is the topological shape of the gravity well by the Sun/BH, and the only objects that may be affected by it, are comets and Asteroids that stray within a certain distance of the Sun/BH, remembering that a BH is not an all purpose infinite vacuum cleaner.