Heiwa wrote:sceppy wrote:The reason a water hose works and pushes a fireman back, is the pressure of the jet of water against the air.
Can you pls illustrate above with a figure? Evidently there is an invisible friction force between the static air and the flowing water that has left the hose, but how does this invisible force apply to the fireman?
I have a feeling you do not know anything how a force works.
Molecules that make up air are always in an agitated state. It's just a case of how agitated depending on how hot or cold it is.
It's the reason why we feel hot or cold.
When we are cold...it's because the air molecules are slow and laboured all over our skin.
If it's hot weather...those molecules are as agitated as hell on your skin and it's that friction that heats you up to make you sweat to cool them down to a less agitated state.
I'm telling you this because most people do not understand the force of the atmospheric pressure we are living under and they pass it off as nothing.
I mean, we can wave our arms about, so what's the problem, right?
Well that's fine, because our bodies equalise that pressure and we are born with it around us, so we never give it the thought it deserves.
Now that's out of the way, I'll explain why the hose works against the atmosphere.
Oh... one more thing. I'll just explain what air pressure is and does.
As we know...air pressure is at 14.7 psi at sea level and the reason for this is because the air molecules are stacked on top of each other for miles and miles into the sky.
At sea level, the air molecules are compressed by the air molecules above them and so on and so on, until the air molecules at the top are basically left to run about like free range hens because there is very minimal compression force acting on them, so they can move around each other at fast pace.
This is known to us as thin air.
To really appreciate the power of atmospheric pressure at sea level, we can pressurise a container, or we can partially evacuate one, depending on it's strength.
So what happens when we put 1000 psi above atmospheric pressure into a sealed container?
Well first of all we have to remember that the empty container already had 14.7 psi inside it, when open to the air, because it was equalised in pressure, so the container is only under the stress of its own weight and make up.
Ok, so now it has 1000 psi extra inside it, which means, the molecules are squashed together like a bus full of kids with squashed faces against the windows of a bus.
In this state, the molecules are all fighting against each other, trying to push back against each other to get out of the way so they can regain their natural size but they find it hard, due to the amount squashed inside the container.
So where did that extra 1000 psi air come from that went into that container?
It came from the atmosphere at 14.7 psi and was squashed into a cylinder, so the atmosphere from above, has to naturally fill in the air that was taken...but how can it do this when the air is inside a solid container?
Because 1000 psi was taken from the air, it is replaced.
The thing to remember here,is...no matter what you do on earth or what happens...
everything has to have an
equaland opposite
reaction to every
action and it's the same with air.
You take 1000 psi from the air (action) and the air replaces as you take it (equal reaction to action).
If you compress 1000 psi of air molecules inside a container, the air outside will equalise that pressure over the outside surface area applying more volume of pressure at 14.7 psi.Or to put it simpler, there is an extra 1000 psi spread over the entire surface of the cylinder to equalise that pressure all pushing against it in a more agitated state than those inside.
A classic example is your common party balloon.
If you blow it up. The compressed air expands the balloon but the air molecules are
squashed and because this balloon is attempting to defy sea level atmospheric pressure, then atmospheric pressure will
equally concentrate and equal pressure against the pressure inside the balloon by becoming more pushy against the molecules that were taken from the atmosphere.
Hopefully this will be understood by all, because it's important to know the strength of what we live and breath under.
Ok, so let's get back to the fire hose because this trick is used to dupe people and it works well at first glance because it appears that it's correct in how rockets work so very few question it.
For all you logical thinkers (of which there are a lot of you) I'm 'hopefully' going to nail this once and for all in this post.
Rocket scientists would like us all to believe a rocket works like a fire hose. So let's grasp how one works how they say.
The water tank in the fire engine is pressurised and is sent to the hose... and as long as that hose nozzle is shut, the hose will simply hold the water pressure and that's it.There won't be any flopping about or anything like that.
Once the nozzle is open, the water pressure hits the inside of the thinner nozzle which forces the fireman back because there is more pressure coming at the nozzle than the nozzle will allow through, so, action and reaction forces the fireman back and that's why you see them struggling to hold the hose.
The above explanation is N.A.S.A 's supposed rocket and it sounds about right and very plausible doesn't it?...and we aren't rocket scientists so why question it, right?
Well first of all. The explanation for how the hose works, is an utter, pure, ridiculous load of horse shit.
Here's what really happens and bear in mind you need to get an understanding of atmospheric pressure in how I explained it.
For every action, there MUST be an equal and opposite reaction which includes water against atmosphere.
When the water leaves the hose under huge force, it hits the atmosphere and slightly fans out the further it goes, which is important, because the further the water stream goes, that's how much atmospheric pressure is working on it, plus the floor and the building it hits.
Because water is much denser than atmospheric air, it will naturally push that air out of the way much much more quickly... and the air wants to occupy the space what the water has taken, because it's atmospheric pressure has been altered.
Water in its dense state, naturally wants to be under the atmosphere , because it's heavier, yet because it falls naturally under it's own weight in the air, it allows the air to equalise the push against its weight, which is what you see from the stream of water.
So how can a water jet be pushed back by a so called piddly weak looking atmosphere, in simple terms?
Here is the nail in the coffin.
If you shoot water horizontally, you will notice it forms and arc.
This is the key to the fight back by the air, because the top of that water arc is the strongest force against the air, meaning the air has to push on it much harder to try and squeeze it to the ground because that water at the very top is moving horizontally and the water going either way from it is gradually falling, so the air compresses it from all around the water jet and tries to equalise it's own pressure... but in doing so, it forces the water both ways, because, as we know...water cannot be compressed but it can be forced away by exerting pressure, meaning one force hits the building or hits a crowd of rioters and the other force pushes the fireman back.
I'll put in this little diagram to show what I mean and hopefully what I've said will be grasped.
Suggest you join some local volonter fire brigade and test your theory.