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Q & A: Gravitational pull of the Sun

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Most recent answer: 03/24/2011
Q:
how strong is the gravitational pull of the sun
- Zach
Rogers elementary
A:
Isaac Newton found out that the strength of the pull of gravity weakens the farther you get away from an object, in proportion to 1/(r*r), where r is the distance you are away from the center. The strength of the gravitational pull is also proportional to the mass of the object.

The sun is really massive and really big. It has a mass of about 2 times ten raised to the thirtieth power kilograms. (that's 2000000000000000000000000000000 kg), and a radius of about 700000 kilometers.

This makes the strength of gravity on the "surface" of the sun (that is, the photosphere, the shiny part we see), 28 times stronger than the force of gravity on the surface of the Earth. Out here, at the distance we orbit the sun, the gravitational pull of the sun is only 0.0006 of the strength of the earth's gravity on the surface of the earth. But that's enough to pull the entire planet around in a big, nearly circular orbit, once per year. And the variation in the strength of the sun's gravitational pull from the part of the earth that faces towards the sun to the part that faces away is partly responsible for the tides of the ocean. The moon's gravity plays a somewhat larger role in the tides. Although it's weaker than the Sun's gravity here, it varies more from one side of the Earth to another.

Tom (w mike)

(published on 10/22/2007)

Follow-Up #1: gravity and nothingness

Q:
gravity is nothing what you said
- hooly (age 15)
fl
A:
It might help us if you could explain that a bit more.

Mike W.

(published on 03/24/2011)

Follow-Up #2: Rotational speed of the sun

Q:
"The strength of gravity on the "surface" of the sun (that is, the photosphere, the shiny part we see), is 28 times stronger than the force of gravity on the surface of the Earth." Yes, I agree, it is about 27.6 times stronger but I also get a mere 14 days for the photosphere to rotate around the centre of the sun... shouldn't it be more like 30?
- Mangone (age 62)
Thailand
A:
Your idea about the rotational speed of a system being connected with surface gravity is not quite right.    The sun's rotational speed is related to the total angular momentum and the moment of inertia.   Its surface gravity is related only to the radius and the total mass.   The angular momentum and the force of gravity due to mass are different things.  Furthermore, the observed rotational speed of the sun depends on the latitude.  Since the sun's photosphere is gaseous, various latitudes can  rotate at different speeds.
See the article at: http://en.wikipedia.org/wiki/Solar_rotation  for more information.

LeeH


(published on 03/19/2012)

Follow-up on this answer.