objects already moving

dont know if this thr right place to post but here goes...


Physics Question....
Does an object that is already in motion take less energy to keep it moving at its current speed then to start it moving from a static posistion?

any answers formulas or suggestions welcome..

[edit on 10-9-2005 by imbalanced]

I believe, that it depends upon the dencity of the atmosphere, so what magnitude are you talking? Or in generall, because will outwieghers such as a strong wind could seriously hinder the question.

Ask your teacher, if you have one.

Or see if asking Jeeves on AskJeeves.com will work.

[edit on 10/9/05 by The Surrealist]

[edit on 10/9/05 by The Surrealist]

Yes, the amount of energy needed to accelerate an object is higher than than that to keep it alift.

However, Gravity possesses a difficulty for both of them, either of those maneuvers would be easier in a non-gravitational environment

Remaining at a constant speed in outer space is not a difficult task by any means, simply accelerate to the speed you wish to remain and you will remain at that speed forever essensially, or at least until you hit the brakes

THanks for the quick response. I wasnt talking about "lift" by the way.
I was trying to see if a rotating stationary object like a fly wheel would
take less energy to keep its momentum.

[edit on 10-9-2005 by imbalanced]

Actually I think it would take the same amount of energy if it were a stationary object like a flywheel, If anything the acceleration takes up less energy than the momentum because the momentum requires the flywheel to be at a higher speed thus needing more energy. However my best guess is that they both require the same amount (acceleration/starting, momentum/continuation). I doubt I answered your question but you may want to further look into momentum work and energy theorys at this website.
here
Sorry if I wasn't a help

Accelerating anything that stays under constant circumstances (atomsphere, gravity friction etc..) always takes more energy then to keep it at its current velocity.

When keeping something at its current velocity you are only using enough energy to equal the forces currently trying to lower its velocity.

While accelerating you are using that same amount of energy to balance that equation plus more to overcome those forces.

If you can take away ALL forces acting on a object (which I dont beleive we have ever done or is even possible) it takes no energy to keep it at current velocity, but it still takes some although hardly measurable energy to accelerate it. Therfore it does take more energy to start something moving then to keep it moving.

Although very flawed for a true demonstration it does show the basics.. Just get in any vehicle and accelerate. Once you reach a certain speed to maintain that speed you let off of the accelerator "gas pedal, lever, foot pedals". It takes more energy/fuel to accelerate from a stand still or to accelerate to a higher velocity then it does to keep your current velocity. Mainting the current velocity may get harder depending on circumstances but under those same circumstances it is even harder to accelerate. Get on a bike and ride up a steep hill. You'll find it hard to even maintain your current speed and harder to gain speed always, and even harder to start once stopped.


[edit on 11-9-2005 by Xerrog]

[edit on 11-9-2005 by Xerrog]

Thanks Xerrog, that was very help ful post. I understand now about motion and what it takes to keep moving.

basically, if (and this is overly simplified...) you take a body that is standing still and rotate it to 2500 RMP, it will take the same amount of energy to rotate it from 2500 rpm to 5000 rpm as it did to initialize it's rotation. I may be wrong and it may be exponential, though... for some reason I'm thinking that it takes more energy to go from say, 0 to 500 rpm than it does to go from 500 to 1000 rpm... so I guess I can't answer your question :|

I think it would take the same amount of energy.

But we have to remember for a second, An object in motion, will stay in motion unless a force is exerted upon it. An object at rest, will stay at rest, until a force is exerted on it, its basic neuton people

It takes less.

The coefficient of static friction is greater than the coefficient of kinetic friction.

Originally posted by Amorymeltzer
It takes less.

The coefficient of static friction is greater than the coefficient of kinetic friction.

Lol, I was going to say this. Amory is too smart, and too fast.

I took a first year civil engineering course, where we saw this happen again and again. It is harder to get something moving in the first place than it is to keep it going. Think of a heavy object like a refrigerator. If you want to push it down a hallway (for some strange reason) you need to give it a good push to start it going, then it is easier to keep it moving. Just find the heaviest object in your house and do a simple experiment if you still aren't convinced.

An object in motion stays in motion unless another force acts upon it. Its easier to think of in space where there is almost zero gravity. If your flying at 100 m/s it takes no energy to maintain that speed, however it takes a force of for instance 100 N for 1 second to get to that speed.

When you think about rotation and stuff like that on earth its a bit more complex but the same idea applies.