[Joe L. Ogan (OP)]

Does Gravity do any work?  I think there is a school of thought that believes that Gravity does no work.  It appears to me that the concept may be in error.  I welcome comments.  Thanks.  Joe L. Ogan

[Mr. Scientist]

It is in error, because gravity is the same as matter, and since matter does work, the postulation speaks for itself

[Joe L. Ogan (OP)]

Is that really true?  That is a rather clear definition of Gravity.  I wonder why Einstein didn't think of that.  Thanks.  Joe L. Ogan

[Mr. Scientist]

he did

[Farsight]

This is an interesting one, Joe. When we look at something as simple as a waterwheel, we say that gravity does do work. We get hydroelectric power from this, so it looks cut and dried.

But when we look deeper, we see there's something of a problem. Work is the transfer of energy, and if we examine two masses falling towards one another, we know from conservation of energy that no energy is added to the "system" that is those two masses. That's because energy causes gravity, and if energy was really being added, the gravity of the two combined masses would exceed the gravity of the two separate masses.

If the two masses spiralled around one another in a closing orbit and then fused gently and stayed cold, we wouldn't have extracted any work. If however we extracted work from the two masses falling together, the energy we extracted will be dissipated as heat. Then we know from E=mc² that the two masses will then weigh a little less. So the answer is: no, gravity doesn't do any work, but it does allow us to do work.     

[Joe L. Ogan (OP)]

Is Gravity the same as Matter?  Did Einstein so state?  Thanks.  Joe L. Ogan

[Mr. Scientist]

Yes joe. He eqiuavalated gravity to mass and not only gravity, but acceleration and natural distortions.

[Mr. Scientist]

This is an interesting one, Joe. When we look at something as simple as a waterwheel, we say that gravity does do work. We get hydroelectric power from this, so it looks cut and dried.

But when we look deeper, we see there's something of a problem. Work is the transfer of energy, and if we examine two masses falling towards one another, we know from conservation of energy that no energy is added to the "system" that is those two masses. That's because energy causes gravity, and if energy was really being added, the gravity of the two combined masses would exceed the gravity of the two separate masses.

If the two masses spiralled around one another in a closing orbit and then fused gently and stayed cold, we wouldn't have extracted any work. If however we extracted work from the two masses falling together, the energy we extracted will be dissipated as heat. Then we know from E=mc² that the two masses will then weigh a little less. So the answer is: no, gravity doesn't do any work, but it does allow us to do work.     

Farsight.. enough. You have seen my reply - your archiac science has no place when considering these things. Obviously if gravity is a physical force, it must have a work associated to it.

[Geezer]

Farsight.. enough. You have seen my reply - your archiac science has no place when considering these things. Obviously if gravity is a physical force, it must have a work associated to it.

I don't think so. Mr S, I presume you are sitting on a chair. Gravity is exerting a force on you and the chair is reacting to that force to support your mass. While the chair continues to support that mass, no work is done. If the chair collapses and you fall to the ground, work has been done. Just because there is a force it does not mean work is being done.

[Karen W.]

By work do you mean there was no energy expended in sitting down on the chair Geezer?

[Joe L. Ogan (OP)]

Yes joe. He eqiuavalated gravity to mass and not only gravity, but acceleration and natural distortions.

Mr. Scientists.  As you know, I have great respect for your Scientific knowledge.  You have increased my vocabulary.  You have taught me a lot about Science.  But your statement that Mass and Gravity are the same thing begs the question with me.  Please let me explain.  If you give me some Mass, I can measure it, I can weigh it.  I can tell you if it stinks or if it smells good.  I can't do any of those things with Gravity.  It will be very interesting to see you tell me how I can do those.  Thanks for your comments.  Joe L. Ogan

[Geezer]

By work do you mean there was no energy expended in sitting down on the chair Geezer?

Of course work was expended in moving your mass to sit in the chair. But once you sit in the chair, no work is being done. However, the gravitational force persists.

If mass is moved along the direction of the force of gravity, work is done by, or against, gravity. While you are sitting in your chair, gravity is doing no work.

"Ah ha!" you might say, "So why am I still orbiting the centere of the planet? Surely the force of gravity is supplying the energy to make this happen."

Simply, it cannot do that! The force of gravity acts towards the centre (of mass) of the earth. At any moment while you are sitting in your chair, your direction of travel is perpendicular to that force. Unless Einstein repealled the basic laws of mechanics, it is not possible for gravity to propel your movement around the center (of mass) of the earth. Your motion is a function of the friction between you and the earth. The friction is a function of the gravitational force between you and the earth, but unless you move along that gravitational line of force, no work is done by, or against, the force of gravity.

[Karen W.]

Is the balancing you do to stay in an upright position constitute force still happening or does it become different from side to side why I ask this is that when I have passed out in my chair my body has slumped down and out of the chair to the ground where I find myself when I have come too, so is there not a constant work happening in just trying to sit upright in a chair to begin with?

I am not trying to be difficult but to understand as I am horrible with gravity and it is a difficult subject even with basic understandings...

[Geezer]

Is the balancing you do to stay in an upright position constitute force still happening or does it become different from side to side why I ask this is that when I have passed out in my chair my body has slumped down and out of the chair to the ground where I find myself when I have come too, so is there not a constant work happening in just trying to sit upright in a chair to begin with?

I am not trying to be difficult but to understand as I am horrible with gravity and it is a difficult subject even with basic understandings...

No problem. It's quite simple really. If your "center of mass" moved closer to the earth's center of mass when you slumped forward, (which it probably did) then the force of gravity did work. When you realized that you were about to start inhaling your soup, you had to do a corresponding amount of work to straighten yourself up again, and you did that work against the force of gravity.

If you are sitting on an office type chair with wheels, and you scoot across the floor on it, you did some work to do the scooting, but gravity didn't do any work because the distance between your center of mass and the earth's center of mass didn't change (unless your floor has a nasty slope, in which case you should sell your house soon.)

BTW, we are all acutely aware of the force of gravity, particularly as we get older. We tend to take it for granted. We do have a pretty good idea about what it does, certainly in close proximity to our star (the sun), but although we can predict quite accurately what it does, we don't really have a very good handle on how the heck it does it! There are many schools of thought on that one.

[Karen W.]

Thank you Geezer.. I need to contemplate that a while! maybe look up some references..or diagrams..you have any... diagrams that is? I am a visual girl!

[Geezer]

Le sigh!

[diagram=549_0]

[Geezer]

As Cyril Fletcher put it, "The effects of gravity can be grave."

Seriously, gravity is a major embarrassment to modern science. We are all continuously aware of the effects of gravity. Scientists can describe very accurately how gravity influences all objects with mass, but (as far as I am aware) there is no consensus in the scientific community that describes how gravity actually manages to exert its invisible force.

We can talk all we want about the other forces in nature, but if we can't even explain gravity, why would we believe any of them?

(I'm heading for my underground bunker right now.)

[Mr. Scientist]

I give up. I am telling you all, there is work assocoiated to the gravity of something. If it didn't, gravitational objects could not move. It's very simple.

[Mr. Scientist]

Is the balancing you do to stay in an upright position constitute force still happening or does it become different from side to side why I ask this is that when I have passed out in my chair my body has slumped down and out of the chair to the ground where I find myself when I have come too, so is there not a constant work happening in just trying to sit upright in a chair to begin with?

I am not trying to be difficult but to understand as I am horrible with gravity and it is a difficult subject even with basic understandings...

Hi Karen

It's technically true to say there was a gravitational work being done - such things are possible for objects and its called a gravitational potential. However, most of the atoms in your body are able to sit down because of electrostatic repulsion, where all the electrons that are in your body which meet the chair all repel each other like little magnets, so in most cases scientists prefer to think of it being far more ovewhelming than lets say a gravitational influence.

[Mr. Scientist]

Farsight.. enough. You have seen my reply - your archiac science has no place when considering these things. Obviously if gravity is a physical force, it must have a work associated to it.

I don't think so. Mr S, I presume you are sitting on a chair. Gravity is exerting a force on you and the chair is reacting to that force to support your mass. While the chair continues to support that mass, no work is done. If the chair collapses and you fall to the ground, work has been done. Just because there is a force it does not mean work is being done.

Now you're talking rubbish.
To have any physical system do work, there must be a force applied to it. This was simple Newtonian dynamics. The chair collapsing does not because of the overwhelming electrostatic force, not the gravity which almost surely cancels out.