Question for astronomy and physics buffs

[L6steel]

I thought it was the other way round. I thought the planets were losing speed and winding down towards the sun and eventually hitting it therebye giving it more mass.

 

[Kalindras]

It is a balance, but hardly a delicate one. The earth's orbit was probably not affected by the asteroid that killed all the dinosaurs, for example. The energy it would take make minor changes in the orbit is too huge.

Everything is relative. When an object of, say, 60 trillion tons gets slammed by a ten-thousand ton asteroid--no, it's not even a hiccup.

The viewpoint might be different if you were standing at ground zero when it did, though...

Heck, astronomically speaking, our solar system, with its "vast expanses" is a mouse fart in a hurricane. So is our galaxy, our quadrant, or even EVERYTHING (as we know it from observations). Like Douglas Adams mentioned in HHGttG, "Space...is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the street to the chemist, but that's just peanuts to space."

 

[Grover_Cephas]

I thought it was the other way round. I thought the planets were losing speed and winding down towards the sun and eventually hitting it therebye giving it more mass.

I suppose the planets must be slowing, right. I mean, if nothing else, there'd be friction with interplanetary hydrogen, right? And impacts with asteroids moving _against_ the Earth are likely to transfer more energy than those moving _with_ the Earth, so on average we should be slowing somewhat. But in any event, the mass of a planet (even one of the big ones, like Saturn and Jupiter) would be meaningless compared with the amount of matter being ejected and converted to heat, light, and radiation. The planets are unimaginably small relative to the Sun.

I have another question, though. A few people have remarked that the planets' revolutions are slowing due to tidal forces... I know that the deformation of planetary surfaces (in water, like on Earth, or in stone, like on the Moon) slows the _rotation_ of orbiting objects, but how does it influence the speed at which the object moves through space?

 

[klattman]

...
I have another question, though. A few people have remarked that the planets' revolutions are slowing due to tidal forces... I know that the deformation of planetary surfaces (in water, like on Earth, or in stone, like on the Moon) slows the _rotation_ of orbiting objects, but how does it influence the speed at which the object moves through space?

Think about what causes the tides on the earth... then think of the deformation and tides as a resistance to that cause.

Let's see if anyone can answer without google, or at least cite stuff that they cut and paste.

 

[Eric1115]

Think about what causes the tides on the earth... then think of the deformation and tides as a resistance to that cause.

Let's see if anyone can answer without google, or at least cite stuff that they cut and paste.

Easy. Gravitational forces from the moon. As Earth rotates, its position relative to any place on Earth changes. The water in the oceans is actually being pulled toward the moon.

 

[Larry B.]

Early in the Earths history the moon was only about 25,000 miles away, and every wave was a tsunami.

 

[johnniet]

Think about what causes the tides on the earth... then think of the deformation and tides as a resistance to that cause.

Tidal forces have to do with the fact that the gravitational force changes with distance. In other words, the water closest to the moon(!) is pulled just a bit harder than the water in the middle, which is pulled harder than the water on the opposite side of the earth. At the same time, the total volume of water has to stay the same...
I don't remember how it all works, but it turns out that the way to balance tidal forces with earth's gravity and water pressure is: the water on the earth's surface is kind of "stretched" in the direction that goes toward the moon.
The water closest to the moon is pulled up.
The water level around the middle sinks a bit, because it can get closer to the moon by moving toward the center of the earth.
But the volume of water has to stay the same, so the water level actually rises on the far end also. That is where the moon's gravity is weakest and the pressure from all the other water on the planet pushes it up.

 

[klattman]

All very good responses, and correct too.

Don't forget that the Earth is pulled _away_ from the water opposite the moon as well, so there are two high tides each day. Water is 'stretched' from the Earth toward _and_ away from the moon.

Fun stuff huh?