# A good way to look at gravity?

• Nexus555
In summary, the conversation discusses the concept of gravity and how it can be visualized in a physical sense. The "balls on a rubber sheet" model is mentioned and it is explained that this model is commonly used in general relativity, but it oversimplifies the concept by focusing only on the curvature of space rather than also considering the curvature of time. The conversation also touches on the mathematics involved in understanding gravity and mentions other analogies, such as a bed sheet representing space/time and a baseball representing a planet.
Nexus555
Hey guys. I know what gravity is and everything, but I was wondering if this would be a good way to look at gravity in a physical sense (even though you can't nessesarily "see" gravity, but observe it's effects.)

Lets say you have a planet, or star. Since there is a lot of mass in the planet/star or whatever, the planet bends space. Would this be a good analogy since gravity attracts?

I find it very strange how gravity attracts objects. It seems somewhat logical to think if an object is in space, it is pressing "down" on the "fabric" of space. The downward push causes gravity, therefore attraction to the object with suficient mass.

I guess a good example would be this: Let's say you have a bed sheet that represents space/time and a baseball that represents a planet. Now if you stretch the sheet out somewhat tightly with 2 people and place the ball on the sheet, the ball causes the sheet to bend downwards a little bit. Now if you have let's say a marble, and place it on the sheet, if it's close enough, it will "attract" (or since gravity exists on earth, travel downward to the lowest possible point.) However if it's not close enough to the funnel, it stands still, and also causes a small amount of indention to the sheet itself. I know this analogy is flawd in the sense it's on earth, but I'm just trying to generalize and make sense of it!

I'm familiar with Newton's laws and relativity and all, I just want to know a good way to picture it in my head. Please try to verify this analogy or enlighten me! Thanks guys

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That's pretty much the textbook "balls on a rubber sheet" model used for GR, yep.

(In fact - don't take this the wrong way - it sort of indicates that you haven't done a lot of reading on the subject, since you would have stumbled over the rubber sheet model immediately.) You pretty much nailed it.

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You're right lol. I've been out of high school for 4 years and I'm temporarily out of college... The last science last I had dealing with gravity probably was my freshmen year of high school... Didnt' take physics in high school but going for astronomy/physics in 2 years at LSU ! Can't wait!

Nexus555 said:
You're right lol. I've been out of high school for 4 years and I'm temporarily out of college... The last science last I had dealing with gravity probably was my freshmen year of high school... Didnt' take physics in high school but going for astronomy/physics in 2 years at LSU ! Can't wait!

What level is your mathematics?

I have good math skills. I am fully aware of the advanced math involved with physics.

The rubber sheet analogy is somewhat misleading because it's actually the curvature of time that usually dominates. For light grazing the sun, the curvature of space accounts for about half the deflection. See Schutz, Gravity from the Ground Up: An Introductory Guide to Gravity and General Relativity, Ch. 18.

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Nexus555 said:
I guess a good example would be this: Let's say you have a bed sheet that represents space/time and a baseball that represents a planet. Now if you stretch the sheet out somewhat tightly with 2 people and place the ball on the sheet, the ball causes the sheet to bend downwards a little bit. Now if you have let's say a marble, and place it on the sheet, if it's close enough, it will "attract" (or since gravity exists on earth, travel downward to the lowest possible point.) However if it's not close enough to the funnel, it stands still, and also causes a small amount of indention to the sheet itself. I know this analogy is flawd in the sense it's on earth, but I'm just trying to generalize and make sense of it!

that analogy is very similar to the one used by Michio Kaku in parallel worlds

## 1. What is gravity?

Gravity is a fundamental force of nature that causes objects with mass to be attracted to each other. It is responsible for keeping planets in orbit around the sun and objects on Earth from floating away into space.

## 2. How does gravity work?

Gravity is caused by the curvature of space-time, which is created by the presence of mass or energy. The more massive an object is, the stronger its gravitational pull will be.

## 3. Why do objects fall towards the ground?

Objects fall towards the ground because the Earth's mass creates a large enough gravitational force to overcome the upward force of an object's initial velocity. This is known as the force of gravity.

## 4. How does gravity affect the motion of objects?

Gravity affects the motion of objects by causing them to accelerate towards each other. This acceleration is determined by the masses of the objects and the distance between them. The greater the mass and closer the distance, the stronger the gravitational force.

## 5. Can gravity be manipulated?

Currently, there is no known way to manipulate or control the force of gravity. However, scientists are constantly studying and researching ways to potentially harness and use it for future technologies and space exploration.

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