Thread: Attraction

When I think of the gravitational pull of a large body of mass with a magnet, I see a similarity...attraction.

The longer the distance between two magnets, the weaker the attraction. Does gravity behave in a similar manner? For example, when I'm flying 30,000 feet in the air, do I weight less? In the ISS, gravity is measured as "micro-gravity".

Is there a breaking point between 30,000 feet and the ISS where there is a sudden change in attraction to the earth or is it gradual?

I'm just wondering because you hear about weightlessness in space all the time but I have never heard of weighing half as what you weight at sea level at a certain hight.

The attraction decreases in proportion to 1/(distance squared). So not quite gradual, as the attraction will increase or decrease quite rapidly depending on whether you are moving to or from the massive body. But not abrupt either.

You might find it interesting to look up escape velocities on Wiki.

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

Originally Posted by mjr150

When I think of the gravitational pull of a large body of mass with a magnet, I see a similarity...attraction.

The longer the distance between two magnets, the weaker the attraction. Does gravity behave in a similar manner? For example, when I'm flying 30,000 feet in the air, do I weight less? In the ISS, gravity is measured as "micro-gravity".

At 30,000 ft you would weigh about 99.7% of what you would on the surface.

Is there a breaking point between 30,000 feet and the ISS where there is a sudden change in attraction to the earth or is it gradual?

Gravity falls off by the square of the distance. In the case of the Earth, the distance is measured from the center of the Earth. Thus if you were twice as far away from the center of the Earth than you are while standing on its surface, gravity would be 1/4 as strong. It just keeps getting weaker with distance but never drops to zero.

I'm just wondering because you hear about weightlessness in space all the time but I have never heard of weighing half as what you weight at sea level at a certain hight.

When objects are in space they are generally in free-fall. For instance, the ISS orbits at an altitude where gravity is 90% of that at the surface. The astronauts inside feel weightless because they are in free fall along with the ISS and are not resisting the pull of gravity.

That explains it. Ok, one more question. If you have 2 magnets at a set distance from one another, there is a definable attraction towards one another.

If you place a knife between the 2, that attraction is interrupted and changed and when you remove the knife, the attraction is restored.

Similarly, if you place a mass between 2 other masses, does the attraction change? For example, during an eclipse, does the attraction between the earth and the sun temporarily slightly change?

You'd have to go up to 8.66 million feet to get to the point where you feel half of Earth's gravity, but yes, you do weigh a little less in an airplane. You'd weight about 0.3% less at 30000 feet above the equator. The Earth isn't quite round enough to give such a small number accurately.

Edit: Ninja'd

Anyway, no. The attraction between the magnets isn't significantly changed by the knife, and the gravitational attraction between masses doesn't care about objects in the way at all. They feel the new mass, but their attraction to the old one is unchanged.

Originally Posted by mjr150

When I think of the gravitational pull of a large body of mass with a magnet, I see a similarity...attraction.

The longer the distance between two magnets, the weaker the attraction. Does gravity behave in a similar manner? For example, when I'm flying 30,000 feet in the air, do I weight less? In the ISS, gravity is measured as "micro-gravity".

Is there a breaking point between 30,000 feet and the ISS where there is a sudden change in attraction to the earth or is it gradual?

I'm just wondering because you hear about weightlessness in space all the time but I have never heard of weighing half as what you weight at sea level at a certain hight.

There is little resemblance between magnetic fields and gravitational fields.

Magnetic and electric fields fall off like 1/distance. (The combined electromagnetic fields fall off like 1/distance^2).

Electric and magnetic fields can change character within a material, and hence shields can be made and electric and magnetic circuits constructed, That is why an intervening piece of iron can affect the force between two magnets,

Gravity falls off like 1/distance^2. There is no effect from an intervening mass other than the addition of the gravitational field of that mass. There is no such thing as a gravitational shield.

Weightlessness is simply a state of free fall. You can experience it on a roller coaster -- exactly the same thing as what astronauts experience in orbit -- it just does not last as long. A satellite literally falls around the Earth.

The gravitational field of the Earth, drops off like 1/distance^2 where the distance is the distance from the center of the Earth (this only applies above the surface of the Earth and not in the interior, as in a mine shaft).

Interesting. I suppose if you could create a gravitational barrier, you could create a pretty cool circus ride.

A photon has no mass, I guess that why it can achieve the cosmological speed limit. I've been told that a photon doesn't necessarily travel,but rather, electromagnetic waves are carried as pure energy through space, kind of the same way energy is carried as waves in the ocean.

Here is another question. If you could snap your fingers and make the sun disappear, it would take about 8 minutes for the earth to be dark, about the time it takes for the electromagnetic waves to travel 93 million miles to earth.

How long would it take for the sun's gravitational pull to cease exerting attraction on our planet? Is it instant?

Originally Posted by mjr150

Here is another question. If you could snap your fingers and make the sun disappear, it would take about 8 minutes for the earth to be dark, about the time it takes for the electromagnetic waves to travel 93 million miles to earth.

How long would it take for the sun's gravitational pull to cease exerting attraction on our planet? Is it instant?

That cannot happen sice it violates many physical principles. Given a false premise, ANYTHING can logically follow. So, the answer to your question is that you are free to conclude anything that you wish, including the negation of that concludion as well as the statement itself.

Gravity waves are predicted by general relativity, and they are predicted to travel at the speed of light.

Well, no information can travel faster than light.

So first off the information that you snapped your finger would need a minimum of about 8 minutes to reach the sun. Then lets assume you magic finger snapping causes the sun to suddenly cease to exist. The information that the sun has ceased to exist can't possibly reach us in less than 8 minutes. Thus the effect can not be instant.