Why don't pebbles orbit mountains?
When you got something with small mass, shouldn't it orbit the closest something with big mass?
The Earth orbits the sun, the moon orbits the Earth. So, why, with just about the same proportions, don't pebbles orbit mountains?
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answers:
Athena say: Earth's gravity is too strong.
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nineteenthly say: Because the pebbles are pulled down by the planet's gravity and gravity itself is a remarkably weak force.
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Raymond say: On Earth, if you are close enough to a massive mountain, your local "vertical" will point ever-so-slightly off your zenith.
Tests have been done to measure this effect, and it exists for real.
However, the pebble is subject to both effect: It is attracted by the Earth, and it is attracted by the mountain. The force pulling it to Earth is a gazillion times stronger than the one pulling it towards the mountain. The Earth wins.
Just like you. You are pulled by the Moon, by the Sun (much more massive than Earth) and by every single object in the universe. The total effect from all these other things is so small (mostly because these objects are so far away compared to Earth) that you remain attached to Earth. You can safely ignore the other effects when you calculate your weight (= the force with which Earth pulls you).
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Jeancommunicates say: gravity
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Jeffrey K say: If the mountain and pebble were alone in empty space and the pebble had just the right speed, it would orbit. But gravity is so weak, it would take millions of years to orbit once, so it would look like it was floating motionless.
On or near earth, both the mountain and pebble will fall to the ground. Unless they are orbiting the earth.
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sophie.aitchison13 say: They do, but just very slowly. And not in the air - on the ground. I did geo-scientific research at Harvard for 17 years back in the 80s and this is a very common question believe it or not! You’re not unique in your thought process.
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Ronald 7 say: You are not throwing them hard enough
Besides Pebbles Flintstone is all grown up now
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ob1knob say: A pebble could orbit a mountain-like asteroid.
Btw I'm sure some do.
The problems with a mountain on Earth are
- Earth gravity which would pull the pebble out of its orbit
- Earth atmosphere which would slow the pebble down, under orbit speed.
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Matt say: Earth has much more mass than the mountain.
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Dances with Weed say: The bigger mass(the earth) pulls everything to the center of the earth. The pebbles and the mountain are gravitationally attracted but infinitesimally compared to the attraction of the earth.
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Tom S say: Mountains are part of the Earth, they don't have a center of gravity separate from the Earth.
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URWHAT? say: Same reason why moons don't orbit FLAT earths!
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quantumclaustrophobe say: There's a few that do...
Here's a pic of an asteroid about the size of a mountain - and it's one of a handful that have moons:
https://upload.wikimedia.org/wikipedia/c...
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cosmo say: If you had a ball bearing out in space far from other masses, you could put a grain of sand in orbit around it. The orbital period would be about 90 minutes, just like an Earth satellite, because the density of the ball bearing is about the same as the density of the Earth.
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busterwasmycat say: well, they try but there is a stronger force that pulls them in a different direction. Still find pebbles accumulating at the base of mountains though. They are failed mountain-orbiting objects.
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D g say: if the mountain was in space then it would definitely produce some orbiting pebbles..
the problem with a mountain on earth is the direction of forces... say some pebbles were flung to orbit a mountain level to the ground.. then what happens is the GRAVITY pulls the objects downward and they fall quicker down then they do orbiting the smaller mass of the mountain.
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Twila say: because Wilma won't allow it
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say: In space it's possible.
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Mj say: The earths gravity is too strong.
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Captain Matticus, LandPiratesInc say: They're not even close to the proportions. The sun is about 333,000 times more massive than the Earth and the Earth is about 6,000,000,000,000 times more massive than a mountain. A pebble has, at most, a diameter of 64 mm and continental crust has a density of about 2.83 g/cm^3
64 mm = 6.4 cm
(4/3) * pi * 6.4^3 * 2.83 =>
3107.5274010251720095080664791973
A spherical pebble of the largest size available for a rock classed as a pebble, would have a mass of about 3 kg. With mountains having an average mass of 10^12 kg, you're looking at a mountain being 3.3 * 10^11 times as massive as the largest pebble, which means that the earth is about 2 * 10^24 times as massive as the largest pebble.
The Earth is about 80 times more massive than the moon
Sun : Earth : Moon => 26,640,000 : 80 : 1, roughly
Earth : Mountain : Pebble => 2,000,000,000,000,000,000,000,000 : 330,000,000,000 : 1
Those are some mighty big differences in scale. Correct your assumptions and you can correct your conclusions.
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drake say: They aren’t dense enough. The closer something gets to the center of mass of an object, the greater the gravitational force experienced. Given the center of mass of a mountain is somewhere deep inside it, things cannot get close enough to it to experience a great of enough gravitational force. This idea goes away when you’re in the mountain or some object. There would be a gravitational force from the layers behind you and it would decrease the net force acting on you, given you’re falling towards the center of the object.
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Zardoz say: The Earth gets in the way.
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poldi2 say: The Earth's gravity is stronger than the mountain, so the pebbles are pulled by Earth's gravity more than the mountain's.
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Bill-M say: Earth's gravity.
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ioerr say: if the pebbles and the mountains were floating out in space somewhere far away from the earth, then the pebbles could indeed be made to orbit those mountains. probably.
they can't do it here on earth because the earth's gravity totally overwhelms them of course
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