Why is the earth flattened at the poles?

Answer 1

The earth spins on its axis, about 1,000 miles per hour.

The earth is not quite completely rigid, and centrifugal force causes mass at the equator to slightly bulge, that causes the poles to slightly flatten.

Answer 2

Although we got centrifugal force as a factor, that is nothing compared to the polar gravitation.
Because of gravitational pull from north and south, earth is flattened, it pushes earth mass sidewards and makes the circumference at the equator greater. So the earth is not a perfect sphere but an oblate spheroid.

It's simply like that, not complicated attribution to a very weak centrifugal force because gravitational pull is greater that even it has a centrifugal force earth is still intact otherwise all objects are already projected away from the mass into the space.

Answer 3

Centrifugal force (from Latin centrum "center" and fugere "to flee") is a term which may refer to two different forces which are related to rotation. Both of them are oriented away from the axis of rotation, but the object on which they are exerted differs.

A real or "reactive" centrifugal force occurs in reaction to a centripetal acceleration acting on a mass. This centrifugal force is equal in magnitude to the centripetal force, directed away from the center of rotation, and is exerted by the rotating object upon the object which imposes the centripetal acceleration. Although this sense was used by Isaac Newton,[1] it is only occasionally used in modern discussions.[2][3][4][5]
A pseudo or "fictitious" centrifugal force appears when a rotating reference frame is used for analysis. The (true) frame acceleration is substituted by a (fictitious) centrifugal force that is exerted on all objects, and directed away from the axis of rotation.
Both of the above can be easily observed in action for a passenger riding in a car. If a car swerves around a corner, a passenger's body seems to move towards the outer edge of the car and then pushes against the door.

In the reference frame that is rotating together with the car (a model which those inside the car will often find natural), it looks as if a force is pushing the passenger away from the center of the bend. This is a fictitious force--not an actual force exerted by some other object. The illusion occurs when the reference frame is the car, because that ignores the car's acceleration. A number of physicists treat it much as if it were a real force, as they find that it makes calculations simpler and gives correct results.

However, the force with which the passenger pushes against the door is very real. That force is called a reaction force because it results from passive interaction with the car which actively pushes against the body. As it is directed outward, it is a centrifugal force. Note that this real centrifugal force does not appear until the person touches the body of the car. The car also exerts an equal but opposite force on the person, called "centripetal force". In this case the centrifugal force is canceled by the centripetal force, and the net force is zero, thus the person does not accelerate with respect to the car.

Answer 4

Uhmmm "centrifugal" force is actually 'Conservation of Angular Momentum"