Why does banging on metal produce a reverberating echo-type sound instead of say, a thick knock-like sound when hitting wood? My assumption is that the space of atoms and vibrations change the intensity, volume, frequency, pitch, and effect. But what about the sound of blowing wind? Or the long booming rumble of thunder? or the sound of a motercycle down the road? What makes these types of sounds what they are, with precise magnitude, frequency, pitch, and intensity?

Example - A road during rains.

proper fertilizer has been applied, moisture is well maintained slightly below field capacity, soil texture is good and fresh soil is added to the divots but the grass does not nesh quick enough.

Not sure if this question can be answered but I've always been intrigued as to what the population density would look like if people returned to the country of thier birth. What would the most populous country be for example?

I have heard that the very cold temperatures we are experiecing can cause diesel to freeze. I heard that the temperature is around -12 degrees, is this true?

I have thought of this question as this can effect everybody.

Say there was a tunnel that went through the centre of the Earth that came out on the exact opposite side to the entrance. If you jumped down it, would you have the momentum to fly out of the other side, or would you be pulled towards the Earth's centre of mass and be crushed? This is assuming of course that the person will not burn :P

Is it better to boil water in a kettle or on a gas hob. Which is better for preventing global warming?

The current high price of electricity and gas makes us all careful about how much we use. But if an extremely cheap form of energy generation was discovered (e.g. nuclear fusion) so that people were no longer worried about their gas and electricity bills, what would be the effect on the earth of the resulting huge unfettered increase of energy usage?

E.g. why does kudzu vine overrun parts of the USA?  Why didn't something evolve locally to take advantage of the same conditions in the same way?

or why did new Zealand's ground-nesting birds have no predators?  Surely one would have evolved before all the nasty little mammals were introduced?