/sci/ - Science & Math

[Anonymous No.7421176]

Take a sphere the size of a basketball.

How much mass would this object require before it could start affecting the local gravity of things around it, attracting them to itself from a distance of say, 50 feet?

[Anonymous No.7421180]

>>7421176
A lot tbh

[Anonymous No.7421184]

>>7421176
Any amount of mass. Gravity doesn't shut off at a certain distance from an object. Even if you put a regular ass basketball 50 feet off the surface of an earth-sized ball of iron, it will affect the iron planet. It will be unmeasurable, but it will still be there.
Put a mote of dust a lightyear away so far in dead space that both the dust and basketball won't be affected by something more massive than either, and it will have a pull on the bit of dust. It will be miniscule, but it will be there.

Pedantry aside, take the equation for the force of gravity and fuck around with it in WolframAlpha to get a feel for what kinds of masses have what kind of effect.

[Anonymous No.7421225]

>>7421184
interesting.
Wolfram Alpha is interesting, too, but it's gonna take me a while to be able to use it and comprehend any of the gobbldygook.

Would said basketball sized object need the mass of earth (but not the volume) to affect objects the way earth's gravity affects them?

[Anonymous No.7421250]

The Cavendish torsion balance experiment (with which Cavendish directly measured the value of the gravitational constant in, like, the late 1700s) used masses smaller than a basketball.

OP, what exactly do you mean by "the way earth's gravity affects them"? All masses, no matter how small, have gravity. It's just proportional to their mass.

[Anonymous No.7421278]

>>7421250
You'll have to forgive my presumptions, I am not a very well educated person trying to convey questions I have of things I do not fully comprehend.

I don't know the proportionality of mass to gravity. I guess that may be what I'm asking.

Just playing around with fantasy/junk physics. Comic book and tabletop level ideas, you know? A theoretical object that can be given increasing mass, and proportionally, affect objects all around it more. How much mass would a basketball sized object need to pull objects under 500 pounds towards it?

[Anonymous No.7421309]

>>7421278
Even a small object will pull, but it pulls with such a small force that it's unnoticeable, or undetectable without a really sensitive balance.

A mountain exerts enough gravity to pull pendulums slightly off-true, a large enough effect that land surveyors have to account for it.

Neither of them pulls hard enough to make an everyday object move visibly (overcome friction, be perceptible by your hand, etc).

So, slightly different question: how much mass would the basketball need in order to make something roll or slide towards it across a smooth table? Things will slide across a table if it's more than, (wild guess), five degrees off-level. That's equivalent to a horizontal force of around tan(5°) = 9% of the vertical force (their normal, Earth-attraction weight). Earth's gravity is about 10 Newton/kilogram, so that means the basketball must be exerting about 0.9 Newton/kg.

Let's say the basketball is 20 feet away (6 meters). Attractive force (in newtons): <span class="math"> F = G { { M_{basketball} \times M_{object} } \over { distance^2 } } [/spoiler]. Rearrange that to <span class="math"> M_{basketball} = { F \over M_{object} } \times { distance^2 \over G } [/spoiler]. F/M is 0.9 Newton/kg, distance is 6 meters, G is <span class="math"> 6.67384{\times}10^{-11} {N⋅m^2 \over kg^2} [/spoiler] according to wikipedia. Do the multiplication, and the basketball's mass must be 486 billion kilograms. That's a lot, a (fairly small) mountain's worth of mass compressed enough that you can get within 6 meters of all of it.

A 1-kilogram ball exerts gravity in the same way, just 1/486 billionth as strong.

[Anonymous No.7421365]

>>7421278
Pic of OP for you all.

[Anonymous No.7422096]

>>7421176
use google retard

[Anonymous No.7422142]

Any mass has an associated gravitational field that extends to infinity. So really any basketball of ordinary mass will do.

[Anonymous No.7422650]

>>7421176
OK I did the math. A basketball sized object with the mass of 14 earths gets you a black hole.

[Anonymous No.7422838]

>>7422650
Pfffft, that only takes one of ur moms.

[Anonymous No.7422845]

>>7421225
Less.

[Anonymous No.7422869]

>>7422838
gertje er wordt geklopt want de bel doet het niet

[Anonymous No.7422893]

If the basketball weighs a pound, then its own gravitational field actually pulls up on the Earth with a pound of force.

[Anonymous No.7422926]

>>7421184
"It will be immeasurable"
no. The ball will exert the same force on the planet as the planet exerts on it.
The planet won't move because it has orders of magnitude more inertia than the ball.

[Anonymous No.7422929]

>>7422926
Won't move much*

[Anonymous No.7424075]

>>7421225
> affect objects the way earth's gravity affects them?

a basketball sized object as massive as the earth would absolutely fuck your shit up from 50 feet due to tidal forces.

[Anonymous No.7424107]

>>7421180
That's not a helpful answer anon.
>smfh

[Anonymous No.7424115]

>>7421225

No. Both the earth and the ball have the same effect to each other.
But only the force is the same.

Since the earth hass much more mass than the ball and there is something called inertia, the ball does change his velocity dramaticly, while we can't messure the change of the velocity of the earth.

[Anonymous No.7424129]

>>7421176
the answer is within your question.

[Anonymous No.7424130]

Any mass you dolt.

[Anonymous No.7424131]

>>7421184
>It will be unmeasurable
uh, you mean in space? or is it just a mad mad mad world.

[Anonymous No.7424142]

>>7422926
This. People always forget Newton's first and third laws.

[Anonymous No.7425289]

>>7421225

It wouldn't need the mass of Earth because you're orders of magnitude closer to its centre of gravity.