# GRAVITY its time we figured it out.

1. Aug 12, 2008

### Thebrokentree

I had an interesting idea and wanted to throw it out there to see if i am not mistaken by my thinking. Since gravity's speed on earth is constant 9.8m/s, i came up with a question.

Do objects accelerate in space if the same force is constantly applied? or does the object's speed remain constant even though the same force is applied?

1. If objects continue to accelerate in space even though the same force is constantly applied, then gravity must be applying 2 forces on an object, one that is pulling, and another that is pushing in order to achieve the 9.8m/s. (I am thinking as though gravity is a wave that pushes outward from the earth then hits a mark outside the earth caused by space distortion then returns to Earth at a bit faster speed causing the 9.8m/s.

2. If objects do NOT accelerate in space if a constant force is applied, then it is difficult for me to imagine that gravity could be a wave because a wave goes from the source outward, kinda like if i threw a stone in a pond, and if the water wave hit a wall, it would generate a returning wave balancing the first. So if a gravity wave is going outward from the earth, then why do objects fall instead of move outward. In this case, i would say there must either be 2 waves or 2 forces acting on an object, otherwise we could not achive a limit of 9.8m/s.

I am not a physicist, i have some physics backround but Gravity has been something ive been thinking about since i was a child

Last edited: Aug 12, 2008
2. Aug 12, 2008

### RoryP

Just two things:
1. Gravity doesnt have a speed! Gravity accelerates everything to the earth's surface
2. The "speed" ( acceleration due to gravity) is 9.8ms-2 not 8.9!

3. Aug 12, 2008

### vanesch

Staff Emeritus
But "gravity's speed" is not constant. What's constant at the earth's surface, is gravity's *acceleration* (increase in speed) which equals 9.8 m / s^2.

edit: perfectly in sync with RoryP

4. Aug 12, 2008

### Thebrokentree

forgive me for the number error on 8.9m/s thanks for the correction. But can objects fall any faster than 9.8m/s on earth?

5. Aug 12, 2008

### RoryP

no worries! :D
i think you need to distinguish between acceleration and speed here. Objects accelerate to the earth at a constant 9.8m/s^2 but the speed at which they fall isnt necessarily always the same, you have to take into account for air resistance ect. The fastest anything can fall to earth is something called terminal velocity which is where they no longer accelerate i.e the force of gravity is equal to the force pushing them upwards (air resistance). So everything accelerates to earth at 9.8 m/s^2 this is always the same but objects can have a different speed dependant upon other factors. This is why objects dropped on the moon will hit the ground at the same time, there is no air resistance so they accelerate to the moon's surface at the same rate and speed :D

6. Aug 12, 2008

### Cvan

Earth is big (massive). Because Earth is so massive, it (warps spacetime) pulls things towards it, like you and me. You and me also pull the Earth, but since it is so massive, that doesn't matter. In the particular case of the Earth, it pulls things (on average, on the surface, without air resistance) towards it at about 9.8 meters per second--every second. So every second that it pulls, it adds up more and more meters per second.
Second 1: 9.8 meters / second falling
Second 2: 18.6 meters / second falling
Second 3: 27.4 meters / second falling
Etc...but after a few seconds, most things stop increasing their speed, and level off at what is called "terminal velocity". This is because air is pushing up against you so much that it counters gravity pulling you down faster and faster, but you're still moving down pretty fast. Everything is basically a parachute from that standpoint, although we're probably not the best thing to strap to a skydiver's back, even we're parachutes!

Edit: As for what gravity really IS--well, it affects everything by "bending space (look some introductory books up about it!)", and there's a lot of talk that gravity is transmitted by really really really really really hard to find particles named gravitons, but no one's ever seen em!

7. Aug 12, 2008

### RoryP

And as a reply to your question, if something in space has a force applied to it, it will move constantly with the force given to it until something applies a resistive force. Until a resistive force is applied it will move forever ( as long as there is space for it to move into) as it will not disipate any of its energy to the surroundings.

8. Aug 12, 2008

### Thebrokentree

hmm ok then that makes it clear. I do know that space distortion has a direct relationthip with gravity. But by what you are saying, this means whatever gravity is, it keeps applying the same force each second causing the speed of the falling object to double in a vaccum. Then, distortion in space is causing not only the bending of space, but acceleration of objects. Perhaps space itself being less or more dense or distorted in some areas is causing objects to move? Is this a safe assumption?

9. Aug 12, 2008

### gmax137

You really need to get a good understanding of what "force" and "acceleration" are before you start worrying about distorting space and gravity waves. Look up newton's laws, figure out what they're saying. Figure out how objects fall if you pretend there is no air. Calculate the acceleration of gravity at the earth's surface, see if you get 9.8 m/sec^2, once you do you will understand what this number is, what it means. Then you will be ready to worry about the air... And then you will be ready to think about distorting spacetime, and waves. But if you don't start at the beginning you will always be confused. Keep trying, it is a fascinating story!

10. Aug 12, 2008

### Thebrokentree

i do know where 9.8m/s comes from, i have calculated it before. i do undrestand the impact air has on objects. I am familiar with the difference between mass, weight, speed acceleration and force. I am trying to undrestand what Gravity is at its core using certain known facts about its' nature while incorporating things that we do know, such as newton's laws and what we are learning. It doesnt take a physicist to undrestand newton's laws, its simple enough for most people to grasp it.
I want to think outside of those laws, because obviously everyone who is thinking according to those laws has not been able to come up with a proven theory as to what Gravity really is. Not that the laws are false, but they are not enough to get to the next step to undrestand and overcome the laws of gravity. We need new laws and new ideas and to think outside the box. Not all is as it seems. I am trying to find the relationship between, space and gravity. They seem to be intertwined but no one seems to be able to tell me how.

11. Aug 12, 2008

### Staff: Mentor

Sounds like what you want to understand is General Relativity, our best theory of gravity. Don't expect a one sentence answer to that question--that's a field of study in itself.

Also, it might be wise to first solidify your understanding of Newtonian gravity (and Newton's laws) before worrying about Einsteinian relativity and spacetime warping.

12. Aug 12, 2008

### metalgirl2045

But Newton's laws are outdated and obsolete to theoretical fundamental physics. I'd hestitate to say "false", as they're very useful to most everyday applications, but certainly not complete. So no, you're never going to get a complete understanding of gravity from them, and no real physicist tries. The "new laws" and "thinking outside the box" incorportaing the relationship between gravity and space already arrived about 100 years ago in the form of General Relativity. GR certainly does take a physics degree to understand, and plenty of people who have studied it at degree level still don't understand it! I did a course on it last academic year and despite passing I cannot provide a summary I'm afraid.

Most physicists I know have no difficulty thinking outside the box, a more common problem is not knowing when to think inside the box!

If you want to take it further, first get a physics degree, then a PhD, then some postdoc experience, then work in theoretical physics, then after a couple of decades you might be qualified to start seriously looking into overthrowing Einstein, but don't get your hopes up too high. Otherwise there's a word which begins with C and rhymes with jackpot which you'll very quickly get dubbed as.

13. Aug 12, 2008

### Landru

You like thinking but hate reading books so you're pretty much doomed, having said that I want to point out that gravity isn't a wave because it doesn't (by itself) continuously increase and decrease in any fashion as a wave does.

14. Aug 12, 2008

### Alex6200

That should be meters per second per second, which is an acceleration. Gravity changes your velocity (m/s) at a constant rate, it doesn't change your position (m) at a constant rate. So gravity is measured in meters per second squared, or m/s^2

Since F = ma, acceleration = Force/mass. So if there is a constant force then there is a constant acceleration, not a constant speed.

Try to apply this to everyday scenarios. If you push the accelerator on a car to a constant level, would you expect to tap it and have it instantly go to a constant rate of 50 mph? Or would you expect it to accelerate to 50 mph at a constant rate?

Huh? I have no clue what you're saying. Only one force needs to be applied to give the object a constant acceleration towards the Earth.

If you want to see this in the real world, try jumping off a 2 foot height, and then try jumping off a 3 or 4 foot height (be safe though, k. Maybe try a pool), and think about which collision when you hit the ground is stronger. If you were going at the same speed from both drops, wouldn't they feel the same?

There is no limit to the velocity that one could get from gravity, unless you're bring in another force like air resistance.

Hmm... Maybe look into taking some more advanced physics classes at a community college or something, if you're interested in knowing more about how the physics of the world work.

I personally gained a much more insightful and realistic worldview after I took AP Physics.

15. Aug 12, 2008

### Alex6200

You hit the nail on the head there. Trying to understand relativity before you understand the basics of physics is like trying to solve Fermat's Last Theorem before you know how to count.

16. Aug 13, 2008

Thats what just about every physicist is trying to find out. I'm going to tell you what I tell everyone. Get a book (The the elegant universe by Brian Greene is very good), that has been written by a professor who has had the time to sit down and think of the bast way to explain it. Most people here either don't understand things, understand but can't explain them or over over complicate things (no offence to any one in just generlizing).

17. Aug 24, 2008

### Constructe

In general people use physics to explain phenomena, not exactly understand them. No one can tell you what gravity really is and for the most part, no one tries. They get on with their high paying jobs and try to confuse those that really ask. Physic does however explain the field effects of gravity.

In fact, many say gravity is a particle but can't find a particle. Or they say it's a wave but it doesn't exert wave properties and no one has ever detected a gravity wave, only the non wavelike effects of gravity. So... it is no wonder you are confused. No one will be able to solve your solution unless you want to study it with someone with a new theory or if you simply acnowledge it as a warp in space time. Although you may ask, what is the space time fabric. The questions go on without end...

An open mind and people who encorage you to keep asking is the best solution I can think of.