# Earth Traveling Around the Sun...

This may sound like a silly question to some. But how does the earth continue traveling around the sun without crashing into it? I mean, the pull of the sun’s gravitation seems constant. And the earth has been doing it for presumably billions of years. Yes, I know, it’s called inertia. But how does inertia not violate, say, the law’s against perpetual motion? This is something I have wondered for some time now. Someone please explain it to me.

The Earth’s (and any object in orbit around another) is falling towards the Sun, constantly. The initial velocity and trajectory of an object to another massive one determines whether it’ll crash, fly off or go into orbit.

This site explains it, the picture of the earth with the cannonball was how I first understood it.

OK…reading your question further now, you may actually understand how orbits worked, and you’re asking why the earth’s isn’t slowing down and falling into the sun.

That i’m not 100% sure on, but I guess its because the Sun and Earth’s gravitational interation is constantly attractive, and while that’s there, the Earth wont slow down. It’s not violating the laws against perpetual motion because the Earth isn’t transferring the energy from it’s motion to something else.

There is no law against perpetual motion. In fact, Newton’s first law states that a body in motion will stay in motion unless acted on by an external force.

If you brought a new planet into the solar system and just plopped it somewhere, it would in fact fall into the sun. But if you brought it in with enough veolcity perpendicular to the axis between it and the sun, it would stay in orbit.

Which is clearly what I meant to say. Perpetual motion is happening all the time but the holy-grail of inventors, the so-called perpetual motion devices dont work because they supposedly take whatever’s doing motion, make it do work and not take any kinetic energy/momentum from it.

The earth travelling around the sun is clearly a different case.

There’s no (significant) force slowing the Earth down in its orbit. Living on Earth, where there’s always friction or air resistance to deal with, we expect to see moving things slow down. That doesn’t happen (at least not on the timescale of a few billion years) in interplanetary space- there’s just not enough stuff there to provide enough friction to slow the Earth down noticeably.

The law against perpetual motion machines (First Law of Thermodynamics) isn’t violated here, because the Earth-Sun system (ignoring the moon, all other planets, and in fact the rest of the universe) isn’t gaining energy over time. That law doesn’t say the energy in a system can’t stay the same, just that it can’t increase without energy being put in from an external source. Perpetual motion machines violate the First Law of Thermodynamics, because they start with a system that has some amount of energy, and expect that level of energy to stay the same (or fluctuate, but not have an overall downward trend) even though the system is transferring energy to something else (doing work). The Earth-Sun system isn’t transferring energy to something else (ignoring the tiny bit of friction from interplanetary dust and such), so its energy can stay constant.

Long ago a star exploded. It then condensed into a new star, which converted hydrogen into helium, and eventually that into carbon, and in the final seconds of its life - before it too exploded - it created all the heavy elements of our solar system like mercury and gold and silver and uranium. When this star exploded it threw all that material out very far, and some of the gas recompressed to form a new star - our sun. Some of the particles that were flung out around this sun fell back into it and burned up, others stayed in a perfect orbit around it (well perfect to us, but they too may one day eventually fall back into the sun), and other molecules were flung so far out that they escaped the new sun’s gravity, and exist today as the Oort Cloud which is a full light year now away from our sun (and the source of comets).

These particles that stayed in orbit around our sun eventually collided with one another and formed the planets that we know today. Others just stayed as smaller molecules, like the asteroid belt between Mars and Jupiter, which never formed due to the gravitational pull of the latter.

So, when you look at the planets - they’re the few molecules that chose the perfect orbit around a new sun as to not escape its gravity, nor fall into it very quickly. It’s kind of like a galactic natural selection.

I also wanted to tell you that if you really want to get technical you could read up on Einstein’s General Relativity which says that the massive sun is actually curving space-time, kind of like if you were to hold a piece of paper and place a marble in the center of it. Objects within the affected part of this space - like earth - are actually taking the straightest path through a curved space. But this gets too complicated for me, so you can read about it link

There are forces at work in the Earth-Sun system that push the Earth away from the Sun. I don’t know if anyone has measured with the precision that would be required whether we’re moving toward or away from the Sun.