Galileo's Principle
Air is a vapor (gas), which means that its atoms and molecules are not in such close proximity to each other as in a solid and liquid. So why don't air molecules just fall to the ground? After all, Galileo's principle states that objects should fall to the ground with equal acceleration independently of their size and mass.
Labels: funphysics, thinktank
posted by ToM at
8:28 AM
10 Comments:
Even as a gas, they molecules still bounce off each other randomly. There's enough random movement to keep them "floating in the air". They do become less crowded in the upper atsomphere, and they do "settle" toward the ground, but the ground layer is many miles thick. On a planet with lots of gravity, the gas molucles do become more like a liquid.
What the trick with this question?
Haha some questions are beyond you ragknot
It is a question of balance between the gravitational force that pulls the molecules down, and the pressure of the gas that, statistically, pulls the molecules up.
I kwon that this is not very "scientific", but I'm not in the mood of big thinking right now :)
My last post is awfully confusing, I'm sorry. Let me try again:
Take a point at height h, and another point at height h+dh; the difference in the heights means that there is a difference in the air pressure at both points. if you take a very very very tiny cube with size dh, the cube will feel a force directed from bottom to top due to this difference of pressure (the same happens in liquids, actually).
When this force (impulse) balances the gravitational force applied to the cube, it floats.
Still confusing?
I would think that it is due to the radiant heat of the earth. Heat rises... the gravitational force on the air molecules is overpowered by the force of the radiant heat from the earth. either causing the molecules to float or rise.
They do settle to the ground due to gravity. That's why there's more air pressure at sea level. That's as low as they can go. They don't compact very well, so they stack up. But since they do have mass (and weight), they push down on the ones below creating that air pressure.
The molecules are zooming about, on average, at approximately the speed of sound (that's not quite true). They can't possibly settle down to the ground. The zoom about because they have a temperature.
Right, they do fall to the ground... then they warm, bump, bounce, and build a layer as thick as they can that depends on the heat, pressure, and gravity.
Chris?
Please provide a new ToM.
Hi Ragknot. It'll have to wait until the morning, sorry. I'm done in c/o Gruelling day. I'd actually logged off when I caught your post.
I've decided to quit the 223 problem (gutted). You do come up with amazingly good and original ToM grade problems and angles on them. Thank you.
"Heat rises" is a very common misconception. Strictly heat or heating is about the transfer of thermal energy (from one thing to another).
Most substances, on being heated, expand, decreasing its density. If the substance is a fluid, it will then become more buoyant than its surroundings and float up.
Between 0 and 4 celsius, water does the opposite. It's density increases wih temperature (up to 4 celsius). That's the real reason that the bottom of a pond is the last part to freeze.
Post a Comment
Links to this post:
Create a Link
<< Home