Is a stable orbit technically a perpetual motion machine?

Question

For all intents and purposes is the Earth a perpetual motion machine as it will forever go around the Sun until one of the forces changes(ie: sun goes nova)?

Is there any energy lost in motion through space or is it perpetual?

Answer 1

Earth has been orbiting the sun for billions of years and will most likely continue to do so for billions more. However, the orbit is not perpetual motion in the traditional sense of being able to extract energy from it indefinitely. Any energy extracted from the orbital system, via tides, interaction with the solar wind and other particles, electro-magnetic effects, etc., will cause changes in the orbits or the rotation of the bodies involved. It's just that the "frictional" forces involved are very small compared to the kinetic energy of the system.

The Earth-Moon system exchanges more energy and therefore shows more obvious changes. A billion years ago, a day was only 18 hours long and the Moon orbited once every 20 days. Tidal friction is slowing the Earth and transferring angular momentum to the Moon.

Answer 2

I was thinking the moon around the earth, but it's the same idea, if we discount the effect of friction on the little things that are smacking into us every second.

It's perpetual, but it's not a machine in the sense that somehow we can get energy out of it. When people were searching for perpetual motion, they were going to try to use it for fantastical industrial uses. If you think about the energy in the system though, we can see that taking any energy out of a system that is in equilibrium will change the system.

Answer 3

It depends on what you mean by perpetual motion machine.

Literally it means motion to go on forever. A stable orbit pretty much does just that.

Of course, the perpetual motion machine that doesn't exist (but is none the less searched) for is one whose motion will yield some energy without ever stopping. No energy can be gleaned from orbiting bodies without affecting the orbit itself.

Answer 4

Great question!
Yes, the earth is a perpetual motion machine. There are those who would, wrongly, suggest that the earth doesn't provide energy. You would have to suspend your mental processes completely to beleive this.

1. No other planet provides all of the energy humans and all known living organisms on earth require to live. The rotation of the earth, as well as it's orbit, perfectly regulate the heat, light, oxygen, photosynthesis and everything else that is required for life as we know it, here, on earth.

2. The same energy that is described above also provides wind, water, nuclear, petrochemical and solar energy which we use in abundance. All of these elements are only found on this one planet, in their proper quantities, to support the life we know.

3. Astronomers have now had to concede that there is not another planet like earth within 10 million light years of our planet, which makes earth rather unique, even though there may be thousands more like it out in the universe somewhere.

Your last question was about a loss of energy. Yes, even in space there is some friction and gravitational influences upon the earth. The broader point is how long the earth has maintained the balance of it's inertia. It is truly a miracle.

Answer 5

Nice question. We all like absolutes such as "there is no such thing as perpetual motion". Unfortunately, the earth is slowing down in its orbit by a second or so every few years. This is due to many factors such as tidal effects and gravitational changes felt from the other planets. Also friction in our own orbit is slowing us down. Geologist have shown the our "year" millions (and billions) of years ago was significantly shorter than it is now. I could go on but the bell is about to ring and I have another class coming in.

Answer 6

It's not possible to have a perfectly stable orbit. Both objects would have to be perfectly rigid not to lose any orbital energy through tidal interaction.

Answer 7

The mass of the sun is changing, don't you notice all that light leaving the sun? The earth rotation is slowing down because of the liquid core and oceans. Earth mass is increasing from all those asteroids landing, etc. THE END IS NEAR.

Answer 8

There is always a slight fluctuation in the earths motion...
wait until December 21, 2012, when the planet goes through an Axis shift, woo hoo what a ride that will be...