[neilep (OP)]

Dear All,

An awe inspiring event with devastating consequences too...


mushroom_cloud.jpg (13.64 kB . 300x376 - viewed 7605 times)



Why does a big explosion make a cloud this shape ?......what's going on ?

[another_someone]

Hot air rises.  The original explosion is a big ball of hot air, which then rises, to form the rising crown of the mushroom.  Beneath the rising air, you have a partial vacuum pulling up dust and debris, which creates the stalk of the mushroom.

[Karen W.]

It is usually water vapor and the remnants or debris, from a pretty big explosion.

You know those mushroom clouds are not exclusive to Nuclear explosions.

You can see them  upon other larger explosions like volcano's etc.

It can happen happen like when something slams into the ground to. it causes this hot gas to get down near the ground and the gas rises up quickly making kind of an overflowing funnel that curls over the top forming the mushroom look there, but at the same time it draws smoke, dust and other debris and particles up to make what looks like the stem. The stuff from the top falls out . that is what we know  as fallout! Like when Mt St Helen erupted! the ash from her cloud came clear here in California it was crazy how far it went!

[Karen W.]

Ah You beat me George!

[DoctorBeaver]

They're called mushroom-shaped because mushroom-shaped sounds better than artichoke-shaped  []

[lyner]

you have a partial vacuum pulling up dust and debris,

Naughty boy!!!!
You aren't allowed to talk in terms of 'sucking' these days. Pressure only works 'downhill'. Air cannot pull anything; the attractive force between adjacent molecules is far too small.
The official line, now, is that.
1. The initial explosion raises the temperature of the air, locally.
2. It expands against the surrounding air and the density decreases. (The initial shock wave / blast are outwards from the explosion).
3. Once the initial expansion has finished, the more dense surrounding air produces upthrust and the 'hot air rises'. The hot gases keep expanding as they ascend.
4. The movement is so violent that the speed of the incoming colder air is enough to sweep objects along with it - inwards and upwards.
5. The inflow of air at the bottom constricts the flow so you have a stalk for the mushroom.
6. At a certain height, the vertical speed and inward pressure reduce and the cloud continues to expand, giving the mushroom head.
7. The energy starts of run out; the edges of the cloud start to droop and   you then get doughnut-shaped convection currents.

Much the same thing happens with a normal bonfire; it's just not as impressive.

[another_someone]

Ah You beat me George!

You know I'm not a violent bloke - I would never beat a lady!

[DoctorBeaver]

Ah You beat me George!

You know I'm not a violent bloke - I would never beat a lady!

Lady?

[lyner]

But of course. Innocent until proved guilty.

[DoctorBeaver]

Innocent of what? Being a lady?  []

[lyner]

Exactly.

[Karen W.]

Ah You beat me George!

You know I'm not a violent bloke - I would never beat a lady!

LOL.. Yes I do know that! Your funny George! []

[Karen W.]

Ah You beat me George!

You know I'm not a violent bloke - I would never beat a lady!

Lady?

Who says I am not a lady??? You scoundrel YOU!! [] []

[Karen W.]

But of course. Innocent until proved guilty.

Why Thank you!!

Sorry I posted in your post instead of hitting the quote.. all fixed and My apologies!

[Karen W.]

LOL...Yeah yeah....Good thing I don't bite! LOL! []

[Andrew K Fletcher]

The Mushroom cloud is caused by gravity suppressing the explosion. In space away from the effects of gravity the picture would be completely different. Gravity is the stronger force and easily prevents the explosion from expanding further than a few miles. The gas cloud formation merely adds a visual effect to what is normally invisible to the eye in weather patterns around the world. The Atlantic Conveyor system also uses the same flow and return caused by density changes in the ocean surface water.

The density changes in the air current would not cause the flow and return without gravity (my argument for fluid transport in trees uses the same density changes to show how fluids circulate because of gravity. The same goes for gas and even rocks in giant density flow and return recycling movement.

Andrew K Fletcher

[lyner]

Do you have any supporting Maths and quantitative evidence for this view?

[Andrew K Fletcher]

Do you have evidence that suggests we would get a mushroom shaped cloud in a nuclear explosion in space away from the effects of gravity and the atmospheric pressure generated by gravity? If so could you please explain how the blast would not go in an equal circumference around the explosion without gravity?

The explosion on Earth shoots up because it is suppressed by the surface of the Earth. Density changes in gas and debris are affected upon by gravity, which provides the climate for this observation. No gravity = no mushroom cloud!

If so “do you” have any supporting Maths and quantitative evidence for this view?

[lyner]

We may be talking at cross purposes. I don't think there is a basic disagreement. I think I read your post too quickly! Apologies.
Of course, in space the explosion would be more or less symmetrical. There would be no atmosphere and no convection effects. The blast would just consist of the parts of the bomb case and these would keep going 'for ever'. The mass of the bomb is negligible so there are no significant gravitational forces out there.
But I would disagree with your comment about gravity suppressing the explosion directly on Earth or anywhere. The actual velocity of the parts of the bomb would be well in excess of the Earth's escape velocity. What limits the distance that the bits of bomb and the immediately surrounding air can travel is the damping by the rest of the atmosphere. It's not linear under those conditions but if you consider the work done in expanding a spherical shell of a few km diameter against atmospheric pressure by just a few metres, it's huge. Effectively, the initial Kinetic Energy of the explosion is transferred to the internal (thermal) energy of the surrounding atmosphere.
I think my 'noddy' description of what happens, in my earlier post is reasonable. I have used common terms like convection and pressure wave which don't really need further clarification. The whole situation on the Earth's surface is a result of the presence of gravity, of course.
BTW
I have just looked at your movie of the water circulation which, of course, works because the column of salt solution on one side is more dense than the column of freshwater on the other. The energy for the demonstration / experiment comes from the work done in lifting the salt solution to the top of the loop. Once the salt is all flushed through the system (fallen to the bottom), the circulation will stop; the gravitational potential energy source will have run out.

I notice you refer to 'negative tension' which is not an established term. Are you referring to 'pressure difference" perhaps?

[Andrew K Fletcher]

I guessed you might have misread my post.

The damping caused by the atmosphere is a direct result of the presence of gravity, no gravity = no atmosphere

Well in excess of the Earth’s escape velocity, yet unable to escape from the Earth’s influence proves my point really.

As for the tubular water experiment, 1 grain of salt or sugar can induce the flow when it is added above ground level to either side of the water filled column, and if added at the top of the loop of tubing at 24 metres, then as it falls it creates a dragging effect on each of the water molecules causing the entire water filled column to rotate as the less dense fluid is pulled up to replace the denser water flowing down. 1 grain of salt or sugar can induce this flow. And more than 1 grain of salt or sugar are present in the leaves and fluid at the canopy of a tree. All that is required to induce this flow is to concentrate the fluids in the downward flow slightly more than in the upward return flow and we have induced a powerful yet hitherto overlooked non living physical force which must take place due to the massive concentrating of fluids as they flow from leaf to leaf evaporating 99% of all the water drawn through the roots.