Does the gravitational attraction of the sun on the planets act as a centripetal or as a centrifugal force explain?

Answer 1

By definition, a centripetal force is a force towards a central point, exerted on an

object following a curved path. It causes an object to follow a curved path, such

as an orbit; this is what the gravitational force of the sun does to planets. So it

is clearly a centripetal force.

A centrifugal force is defined as a force that is exerted away from a center

around which an object either rotates or revolves. Literally, in terms of etymology,

centrifugal means fleeing the center. Planets orbit the sun because of a balance

of centripetal and centrifugal forces. If there were only an attractive force pulling

a planet toward the sun, the planet would fall into the sun. And if there were only

a centrifugal force pulling planets away from the sun, the planets would fly out of

the solar system and into interstellar space. But since these two forces are balanced,

planets remain in orbit around the sun.

An object on which the forces are balanced travels in a straight line at constant

speed. The planets do not travel in straight lines or at constant speeds, because

the forces on them are not balanced. The only force on a planet is the centripetal

force of gravitational attraction between it and the sun. That single force produces

all of the orbits we observe, whether elliptical (repeating) or hyperbolic (not repeating).

Those orbits are fairly easy to derive using Newton's formula for gravitational force

and direction, plus some geometry and some calculus.

Non-furious comments: I avoid writing "centrifugal force", by writing "centrifugal effect".

I think that's more or less OK, depending on your "audience".

Technically "centrifugal force" is called a "fictitious force".

It is actually correct to use it in a rotating frame of reference.

Unfortunately, it is often used incorrectly, even by educators.

Luckily, the answer to the question was "centripetal force".

<<>> The physical processes are that there is a force of gravity pulling the Sun and Earth towards each other. The force acts equally both ways, producing an acceleration in both objects, towards each other, following Netwon's second law: force equals mass times acceleration. The Sun's much greater mass means that its acceleration is small, while the Earth's acceleration towards the Sun keeps it in its elliptical orbit. That is what's happening, so for those who can't remember the difference between centrifugal and centripetal, don't worry, they are not terms used by astronomers.