what is it that causes planets to orbit the sun?

Question

I thought that gravity pulled smaller objects to larger objects. How come the earth doesn't fall into the sun???

Answer 1

Sorry folks - gravity is only "half the equation"

For an orbit to exist, there is a fine balance between gravity, which causes objects with mass to be pulled towards each other, and the object's (in this case, planet's) original inertia (its tendency to move through space in a straight line). If the inertia is too high (compared to gravity) the planet achieves "escape velocity" and leaves orbit; if the inertia is too low, gravity wins and the planet falls into the sun - phisssssshhhh

Answer 2

It might help to think of it like this. Gravity is pulling each planet into the sun. However, at the same time, the planets are all moving forwards. An orbit just means that the speed of the planet falling into the sun is exactly balanced by the speed of the planet moving forwards - so, if you like, the planets are falling into the sun but forever missing.

Answer 3

Prof Kevin has given the best explanation as far as I'm aware.

In essence it is gravity that causes planets to orbit. Newton's Law of Motion says that things will continue to travel in a straight line unless something stops it. So our Earth, for example is always on the move, but it is being continually pulled off course by the massive warping of space-time by the sun.

Answer 4

The planets own forward motion being bent around the sun by its gravitational pull. The planets are actually falling closer toward the sun with every completed orbit in an ever diminishing spiral.

Answer 5

Gravity. (Or the bending of space around massive objects such as the Sun).
But the trajectories of the bodies in the solar system may be different. The planets that we see are still there because their trajectories are elliptical. Many other bodies we don't see anymore have fallen into the Sun and some still do.
Most comets follow elliptical trajectories with one focus being the Sun and the other focus of the ellipse very far away.
There are (or can be) objects such as comets which follow hyperbolic trajectories. They approach the Sun, travel around it and then run away, never to return to the solar system.

Answer 6

gravity is the long answer short. for more detail see the work of sir isaac newton specifically the three laws of motion. an object in motion tends to stay in motion unless acted upon by an outside force (gravity). the planets are in motion. the gravity created by the sun attempts to draw the planet closer. the planet has just enough momentum to balance the force of gravity and it stays in a relatively stable orbit. the outside force is relatively constant as is the momentum (velocity) and balance is maintained (at least for our lifetimes god willing).

Answer 7

Gravity and Inertia.

Gravity is the sun's pull....have you noticed that if you look in a chart that shows the revolution and rotation times of the inner and outer planets, you will notice that the inner planets revolve faster and rotate slower while the outer planets revolve slower and rotate faster.
They do that because the planets closer revolve faster so that they don't get pulled into the sun, but can rotate slowly because they have rocky surfaces. But the outer planets have no tension about the gravity pulling it in, but it needs to rotate faster to not let their gases go out.

Inertia is something else...Some one chose a path for the planets to go and if they have no problem moving they keep going on forever....

Answer 8

It's a funny little thing called gravity. It's what keeps you on Earth instead of floating out into space.

Answer 9

You have gravity pulling the earth towards it, you also have the inertia of the pulling outward. Luckily these two opposite force equal and that's how we stay in place.

Answer 10

Paul T has given a one word answer that encapsultes the essential qualitites of what might in any reasonable circumstance be regarded and indeed accepted as not only accurate...possibly definitive...and certainly a lot quicker than whaT i AM WRITING NOW.

yES...THAT'S IT!!!...GRAVITY