If the world is round, then how come when you set a marble on the ground it dosn't roll?

Answer 1

That's a cool thing to think about, really!

Same thing as if the world is round, and if we lay down we don't roll around.

The gravitational pull affects al the reasons that thigs don not roll on the earth with out any force acted on them.

The moon pulls on the earth and it isso stong objects stay in place!!

The world is a tricky place I tell ya!!!

Answer 2

It has to do with a couple of things.
First, the pull from gravity is straight down to the center. Kind of like if you balance a book on your head. The gravity pulls straight down but if your head is directly below the book it has no where to go.

Second, the world is a LOT bigger than a marble (25,000 circumference I think, although it isn't perfectly round). Anyway, since the Earth is that big it, to something small (like a human or a marble) it is perceived as flat. Thats why back in the day people thought it was flat. Because their perceptions didn't convince them otherwise (maybe they were doing this marble test!).

Third, everything has friction, because no sufrace is perfectly smooth. This is what prevent the rolling. The marble might roll a little and then get stuck in a microscopic groove you couldn't possibly see.

Hope that helps. Good question.

Answer 3

On a spherical world, gravity tends to pull objects towards the centre of the sphere. Objects left on a surface will tend to roll only if there is a direction, in their immediate vicinity, that takes them closer to the centre of the Earth AND if the friction is small enough to allow the object to move.

If, around the marble, all the ground is at the same distance from Earth's centre, then the marble will not move (there is no "downhill" direction). Even if the ground is slightly uneven, it is possible that friction prevents it from moving (ask a golfer whose ball, perched on the edge of the hole, refuses to move the extra millimeter because it is stuck on a blade of grass).

Because the Earth is so large, it is difficult to tell if a surface is truly "flat" or curved along Earth's curvature. However, there are some exceptions.

For example, some very long suspension bridges were built such that the two supporting towers, each perfectly vertical, have to be slightly further apart at the top than at the bottom, because of Earth's curvature.

For a distance of 1 nautical mile (1.15 statute mile, 1.85 km), the angle difference of each location's vertical is 1 minute (1/60 of a degree). This is not easy to see and, besides, very few people get to work on or own such large objects.

Answer 4

It has less to do with gravity, the size of the marble, or friction, and more to do with equilibrium. The mass of the marble is in equilibrium with the rotation of the earth's mass. Even if the earth had only a minute fraction of its present gravity, the marble would not roll. If the earth suddenly stopped, the marble would take off at 1000 mph and take out the mailman down the street. It has to do with physics, (paraphrased) "an object at rest will remain at rest until acted on by another force, an object in motion will remain in motion until acted on by another force".

Answer 5

Which way would you expect it to roll? If the world were truly and perfectly round, and polished smooth as glass, a marble set down upon it would be sitting on a point directly over the center and would tend to want to roll in all directions at once. Since it cannot roll in all directions at once, it stays still. This by the way, touches on some principles of orbital mechanics, and begins to explain why objects can be placed into orbit and fly around the earth. It's all part of the same idea. The only difference is in adding a horizontal motion sufficient to overcome the downward acceperation of gravity. Send the marble rolling off in any given direction fast enough and it would go into orbit.

Answer 6

The pull of gravity in the earth is towards the center of mass, which is also the center of the earth. The pull next to you on the ground is just as far away from the center of mass as the first place.
It won't roll unless the ground around it is not perpendicular a line going to the center of mass for the Earth.
It is also not rolling because the rolling resistance is greater than any force on it including any sideways force.

Answer 7

friction
generally gravity pulls the marble down.
if the world would be perfectly round it would tend to roll in any direction on the slightest force acting on it.
then it would roll around on the surface till friction eats up any kinetic energy and the marble comes to rest again.

in the real world noting is perfectly smooth and if you imagine the marble to fall into a sandpit .. well .. where should it go ?
acutally its friction keeping the marble in place, and gravity holding it down

Answer 8

Because nobody told the marble that the Earth is round.

Answer 9

Because of earth's gravitational pull

Answer 10

because of gravitational force