totse.com | Sun's gravitational pull

irresponsible activist · #1 2008-07-12, 16:39

This is what keeps the planets in orbit right? How come every planet doesn't get sucked into the pull of the sun and get closer to the sun?

gforce · #2 2008-07-12, 17:03

Because the force of gravity by the sun is equal to the force required to 'turn' the planet. Imagine swinging a ball by a piece of string over your head. The tension in the string represents the force from the suns gravity which is equal to the force needed to change the direction of the ball. If the forces are equal (well approximately) then there will be no (significant) change in distance.

willancs · #3 2008-07-12, 22:10

Quote:

Originally Posted by gforce View Post

Because the force of gravity by the sun is equal to the force required to 'turn' the planet. Imagine swinging a ball by a piece of string over your head. The tension in the string represents the force from the suns gravity which is equal to the force needed to change the direction of the ball. If the forces are equal (well approximately) then there will be no (significant) change in distance.

This. The planet wants to continue in a straight line, the gravity pulls it inwards, so as a result it goes between the two forces, and this results in circular motion.

http://en.wikipedia.org/wiki/Centripetal_force

irresponsible activist · #4 2008-07-12, 22:13

Alright

+1

Nightside Eclipse · #5 2008-07-13, 02:25

Centripedal force:

a*R = v^2 (acceleration * radius = velocity^2)

Basic force equation:

F = (G*m1*m2) / R (force = universal grav. constant * mass of object 1 * mass of object 2 divided by distance between them)

Newtons equation:

F = m a (force = mass * acceleration)

Subbing all 3 together, eventually gets you v = sqrt (G*M of sun), where g = 6.67 x 10^-11, and mass of the sun is like 1.0 x 10^31 kg

It goes into something else from there, but thats getting into upper year phys (univ)
Even though some aren't directly related, through a matrix eventually in some HUGE equation that relates the inward velocity to the centripedal velocity you can find out why they go in circles, just doing the math for v = sqrt(GM) won't get anything right.

royce.beat.man · #6 2008-07-14, 04:02

Quote:

Originally Posted by Nightside Eclipse View Post

Centripedal force:

a*R = v^2 (acceleration * radius = velocity^2)

Basic force equation:

F = (G*m1*m2) / R (force = universal grav. constant * mass of object 1 * mass of object 2 divided by distance between them)

Newtons equation:

F = m a (force = mass * acceleration)

Subbing all 3 together, eventually gets you v = sqrt (G*M of sun), where g = 6.67 x 10^-11, and mass of the sun is like 1.0 x 10^31 kg

It goes into something else from there, but thats getting into upper year phys (univ)
Even though some aren't directly related, through a matrix eventually in some HUGE equation that relates the inward velocity to the centripedal velocity you can find out why they go in circles, just doing the math for v = sqrt(GM) won't get anything right.

this^

SelfAdjoint · #7 2008-07-14, 12:57

The same way the moon or satellites don't fall into the earth. (Notice fall, not sucked. I know you know what you mean, but I nevertheless find that kind of inaccuracy annoying.)

SelfAdjoint · #8 2008-07-14, 13:01

Quote:

Originally Posted by Nightside Eclipse View Post

Centripedal force:

a*R = v^2 (acceleration * radius = velocity^2)

Basic force equation:

F = (G*m1*m2) / R (force = universal grav. constant * mass of object 1 * mass of object 2 divided by distance between them)

Newtons equation:

F = m a (force = mass * acceleration)

Subbing all 3 together, eventually gets you v = sqrt (G*M of sun), where g = 6.67 x 10^-11, and mass of the sun is like 1.0 x 10^31 kg

It goes into something else from there, but thats getting into upper year phys (univ)
Even though some aren't directly related, through a matrix eventually in some HUGE equation that relates the inward velocity to the centripedal velocity you can find out why they go in circles, just doing the math for v = sqrt(GM) won't get anything right.

That's for a circular orbit. If you want to do a two body problem (i.e. a planet's effect on the motion of the sun and the sun's effect on the motion of a planet) it gets kind of complicated. If you assume the sun fixed (which to a good approximation it is) and then use Newton's law of gravitation (namely, Force due to gravity=GMm/r²) one finds three possible scenarios for the motion of a planet: an ellipse; a parabola; or an hyperbola.

Mantikore · #9 2008-07-15, 09:56

im pretty sure that the earths linear force is not exactly the same as the force pulling it towards the sun.

so wouldnt that mean the the earth is slowly spiraling towards or away from the sun?

gforce · #10 2008-07-15, 10:43

Quote:

Originally Posted by Mantikore View Post

im pretty sure that the earths linear force is not exactly the same as the force pulling it towards the sun.

so wouldnt that mean the the earth is slowly spiraling towards or away from the sun?

Hence why I said approximately and significant although i cant find any information on whether the orbit is increasing or decreasing but i imagine it is a fairly small amount.