What keeps the planets in orbit in a circle if there is no top and bottom of space?

Question

is there centrifical force in space

Answer 1

Centripetal force

Answer 2

Momentum and gravity.

Edit, centrifugal force is an imaginary force, it does not exist anywhere.

Answer 3

Technically they orbit in an ellipse, not a circle; and centrifugal force is not a real force as such.

But anyway... imagine a sun and one planet.  That planet is moving in a straight line, perpendicular to the line joining that planet to the sun.  This need not be in any particular plane (i.e. top or bottom can be anywhere).  The sun's gravitational field however acts upon the planet, pulling it towards it.  As the planet is already moving though, all this done is change the direction of motion of the planet.  It does this all the way through the orbit, at every moment changing the direction of movement just enough to keep it on the elliptical orbit.

I sense however that your question more referred to why all the planets' orbits are in the same plane.  This is as a result of how the solar system formed.  Initially, it was basically just a big cloud of gas.  Chance movements got it spinning on an axis.  Gravity caused the cloud to collapse into a disk (Reason it wasn't just a smaller cloud was that the rotation caused the matter to stay out of the centre in the plane of rotation).  From the disk, the planets formed.

Answer 4

gravity. they think

Answer 5

God used an antimagnetic field in outer space:

Answer 6

Yes J.N., There is centrifugal force in space.

There is also gravitational attraction between the sun and the planets,

(and between the planets, but it's small and too complicated for now).

The balance between gravity and centrifugal force keeps the planets in their orbits.

Yes, "There is no top and bottom" but also, there's nothing pulling

in those directions.

Answer 7

Actually elliptical orbits---  

Gravity keeps everything in place.

Answer 8

The conservation of angular momentum. It's a basic law of nature. The orbit is usually an ellipse, not a circle.

The vector quantity

R x mV

is a constant for the entire orbit. That's the law of nature. If the planet were to wander out of its normal orbital plane, that quantity could not remain constant.

R = the position vector from the sun to the planet

m = the planet's mass

V = the velocity vector from the sun to the planet

The symbol "x" stands for something called the "cross product." For vectors, more than one kind of multiplication is possible, and the cross product is the kind that gives a vector result. (The other sort, the "dot product," gives a scalar result.)

R x m V = m [expansion of the Matrix below]

Matrix Row 1:  i , j , k

Matrix Row 2: x , y , z

Matrix Row 3: Vx, Vy, Vz

R x m V = m { i ( y Vz - z Vy ) + j ( z Vx - x Vz ) + k ( x Vy - y Vx ) }

where

i = unit vector in the direction of the +x axis

j = unit vector in the direction of the +y axis

k = unit vector in the direction of the +z axis

Usually we assume that the mass of the planet is not changing (or anyway not enough to matter) and treat the quantity

R x V

as a constant for the whole orbit. In other words, you can just leave out the m from the equation above.

Answer 9

It's the massive sun which keep the planets in a same path by it.

Answer 10

Because an orbit is the natural outcome of the interplay between momentum and gravity.  That is, the momentum of the orbiter and the gravity between the orbiter and its primary.

Gravity exists between two masses, and effectively between a point on each mass called the center of gravity.  These two points define a line, and a number of geometric planes can pass through that line.

Momentum is a vector quantity:  that is, it has a magnitude and a direction.  And it is located at the center of gravity of the orbiter.  The vector of the orbiter's magnitude also defines a line.  So the geometric problem is to find the plane passing through the points that define the centers of gravity that also contains the vector of the orbiter's momentum.  That plane is the plane of the orbit.

As gravity acts on the orbiter, it changes the direction of the momentum vector.  But because gravity is acting in the plane defined earlier, it bends the vector only within the plane.  Thus that orbital plane remains self-sustaining.  It takes additional force besides gravity to bend the momentum vector out of that plane.