iWitness - Air Pressure and Weight

Quote from: origamiscienceguy on July 30, 2016, 09:26:44 AM

I see nothing wrong with sokarul's test. Perhapse you could do a better one. Actually, I just did one myself, and anybody here can.

Get a syringe, weigh it.

fill it with a little bit of water. Weigh it again.

Cover the end of the syringe, and pull the stopper to the end, creating a near-vacuum, use a screw or something similar to lock the stopper at the end.

Weigh it again. According to sceptimatic, the liquid inside should be near weightless, so it should weigh the same as when it was empty, but surprise, it doesn't.

Proving that vacuums don't make objects weightless.

I have no chance of explaining something to someone who thinks a syringe is gonna work as an experiment with scales.

Absolutely pointless.

What is wrong with a syringe on a scale?

So if I am understanding scepti correctly the below is would be true if he is right:

If a take a porous material like cork, cover it in plastic wrap and suck the air out it will weigh the same as a piece of iron of the same size.

Quote from: crutonius on July 30, 2016, 10:24:18 AM

Quote from: sceptimatic on July 30, 2016, 09:10:26 AM

Quote from: crutonius on July 30, 2016, 08:56:51 AM

Quote from: sceptimatic on July 30, 2016, 08:35:44 AM

Quote from: sandmanMike on July 30, 2016, 08:30:42 AM

Quote from: sceptimatic on July 30, 2016, 08:01:58 AM

Not correct. It's still under equilibrium.

Could you explain?

If you allow atmospheric pressure to expand and exit out of a chamber, it will still leave an equal (all around inside) but less pressure inside of that chamber. So therefore anything inside it is simply still a dense object sitting inside under that pressure.

I would like some clarification on this as well. It seems like a pretty simple thing to test.

Get a vacuum chamber.

Put a kitchen scale in it.

Put a weight on the scale.

Evacuate the air and then observe.

Yep, as long as the test is done legitimately and not a con job like sokarul tried.

That's kind of the point. These discussions are only a start point.  It's all just a bunch of words until we put it to the test.

I've done this experiment so I can tell you what I've seen. You can my word for it or you can run it yourself. If your results differ from mine then we have to go over our procedures and see who botched what. But if you get the same results then you might have some problems with your theory that needs some work.

That's how falsification works and it takes a certain kind of masochism to perform without prejudice because it's essentially actively working to kill your own intellectual property.

Ok, well first of all, go and get a chamber for pressurising and evacuating. Then do the tests.

Go back and read what I've written more carefully. I have performed these tests.

Quote from: sokarul on July 30, 2016, 09:44:28 AM

The problem is he has claimed air can go through materials at will.

Air does go through materials at will, as long as those materials allow it. This is why they are less dense than other materials that that DO NOT allow air pressure to go through (saturate) them at will.

But high density materials still weigh different. An empty gas cylinder will weigh less than a full one, but no air gets in when it's empty or full. You cannot explain this.

Understand this and you have a chance. Fail to grasp it and you're wasting your time and mine.

Stop claiming the same thing over and over. I have already shown you mean times to be wrong.

Quote from: sandmanMike on July 30, 2016, 08:30:42 AM

Quote from: sceptimatic on July 30, 2016, 08:01:58 AM

Not correct. It's still under equilibrium.

Could you explain?

If you allow atmospheric pressure to expand and exit out of a chamber, it will still leave an equal (all around inside) but less pressure inside of that chamber. So therefore anything inside it is simply still a dense object sitting inside under that pressure.

But if you remove the air, then nothing is pushing down on the object to cause weight.  The absense of air pressure would be the absense of weight in ya'lls definition.

So, if someone was in space, and they just twitched a muscle, they would be ripped apart because all of their body parts suddenly shot off at light speed in different directions?

Congratulations! The experiment proves a Bowling Ball is more dense (heavier) than little to no air (i doubt a true vacuum is even possible).

Congratulations! The experiment proves a Bowling Ball is more dense (heavier) than little to no air (i doubt a true vacuum is even possible).

Density does not mean weight.

Congratulations! The experiment proves a Bowling Ball is more dense (heavier) than little to no air (i doubt a true vacuum is even possible).

But you agree you can lower the air pressure correct?  You've not really confirmed anything I've asked of you yet but I'll try again.

Your assertion is weight is caused by the pressure of air pushing down on objects.  And that the difference in weight when objects are being subjected to the same air pressure is because of density. 

Am I correct in your assertions?

What about baloons? They also have the same amount of air "pushing them down" as everything else.


Or what about a metal stick. If you put it vertically, it weighs the same as horizontally, even though there is much less air above it "pushing it down" when it is vertical.

Air (or water) pressure cannot possibly cause what we call "weight" simply because air is a fluid.

Pressure in a fluid always causes a force at right-angles to the surfaces of any objects in it.

So if we have a horizontal flat sheet the force pressing down on the top surface is balanced by an equal force pressing up on the bottom.

It does not matter how high or low the pressure is the same thing applies, as long as the pressure on the top is the same as the pressure on the bottom. So the pressure does not cause any nett downward force, so does not contribute to weight.

Now we know from measurements that the air pressure gets lower as we increase in altitude.

Intuitively it would seem that this cannot be a very great amount, but it is more than we realise. A helium balloon floats simply because the air pressure pressing up from underneath is slightly greater than the air pressure pushing it down.

The amount of this lift can easily be calculated. A cubic metre of air (at STP^[1]) weighs 1.225 kg, so the air pressure decreases by 1.225 kg per square metre for each metre increase in altitude. This sounds a lot until it is realised that the normal air pressure is 10,340 kg/m².

So back to our funny cube shaped helium balloon, the total force caused the pressure on the bottom is 1.225 kg more than the force on the top, so there is a nett uplift of 1.225 kg.

Now of course we have to subtract from this the weight of the balloon. If we can neglect the weight of the balloon skin, the weight of the helium would be its density (0.164 kg/m³) times its volume (1 m³), or 0.164 kg.

So a 1 cubic metre helium balloon has a buoyancy of just over 1 kg, less the weight of the balloon structure. 

In the end the shape of the balloon makes no difference and the "lift" is simply the
In other words Archimedes Principle.

So, certainly density comes into working out buoyancy,

[1] STP is short for Standard Pressure and Temperature, ie sea level,  etc.

Sceptimatic, iWitness, and Anarchist, I want you to listen to this. 

Imagine you're in the KC-135 "Vomit Comet," the plane used to train astronauts for microgravity.  The plane starts to accelerate downward at 9.8 m/s², and you start to become weightless, along with everything else inside the plane.  But the pressure in the plane hasn't changed at all, and you're not in contact with the outside air, so if weight is caused by pressure and density instead of gravity, how can that be?

Think of the dropped lift. If it dropped at the same speed as you fell and there were scales on the floor with you on them, then you would basically (as a man made weight measurement) weigh nothing.
Now imagine the lift ascends at speed and you are on those scales. You now appear to weigh a lot more due to the force upon you.

Basically in the plane or lift you are free falling (sort of) but due to your enclosed environment, you simply appear to float.
The plane pressurises a lot more on the dive, aiding in that apparent ease of free fall (float appearance).

Ascending in a lift at speed/acceleration is pushing you into atmosphere that is resisting that push. Think of a spring.
This creates more pressure upon you and it would be registered on a scale plate if you were stood on it.
It's made out to be G-force but the real name for it should be A-force.

Quote from: sceptimatic on July 30, 2016, 12:01:08 PM

Quote from: origamiscienceguy on July 30, 2016, 09:26:44 AM

I see nothing wrong with sokarul's test. Perhapse you could do a better one. Actually, I just did one myself, and anybody here can.

Get a syringe, weigh it.

fill it with a little bit of water. Weigh it again.

Cover the end of the syringe, and pull the stopper to the end, creating a near-vacuum, use a screw or something similar to lock the stopper at the end.

Weigh it again. According to sceptimatic, the liquid inside should be near weightless, so it should weigh the same as when it was empty, but surprise, it doesn't.

Proving that vacuums don't make objects weightless.

I have no chance of explaining something to someone who thinks a syringe is gonna work as an experiment with scales.

Absolutely pointless.

What is wrong with a syringe on a scale?

Because the scale is outside with the syringe on it. It's not even an experiment at all.
Try and understand what's being talked about.

So if I am understanding scepti correctly the below is would be true if he is right:

If a take a porous material like cork, cover it in plastic wrap and suck the air out it will weigh the same as a piece of iron of the same size.

In a way, yes but you have to understand that you can't just put it in plastic wrap and suck the air out and see it as a cork.
Think carefully about this.
To evacuate the air from the cork you would shrink that cork severely.

So let's put this into perspective.
To make the cork as dense and weigh the same as iron at the same size ( say a 1 inch diameter iron ball) you would first have to start off with a cork about the size of yourself. Then you encase it in  strong plastic (assuming we could) and evacuating the air from the cork. The plastic will then crush the cork down as long as their is air inside of the cork. If the pump was strong enough to allow the air to evacuate then the cork would be crushed by outside pressure, down to the size of your iron ball and would weigh about the same. It would be just as dense.

Can you understand what I'm telling you?

Quote from: sceptimatic on July 30, 2016, 12:05:47 PM

Quote from: crutonius on July 30, 2016, 10:24:18 AM

Quote from: sceptimatic on July 30, 2016, 09:10:26 AM

Quote from: crutonius on July 30, 2016, 08:56:51 AM

Quote from: sceptimatic on July 30, 2016, 08:35:44 AM

Quote from: sandmanMike on July 30, 2016, 08:30:42 AM

Quote from: sceptimatic on July 30, 2016, 08:01:58 AM

Not correct. It's still under equilibrium.

Could you explain?

If you allow atmospheric pressure to expand and exit out of a chamber, it will still leave an equal (all around inside) but less pressure inside of that chamber. So therefore anything inside it is simply still a dense object sitting inside under that pressure.

I would like some clarification on this as well. It seems like a pretty simple thing to test.

Get a vacuum chamber.

Put a kitchen scale in it.

Put a weight on the scale.

Evacuate the air and then observe.

Yep, as long as the test is done legitimately and not a con job like sokarul tried.

That's kind of the point. These discussions are only a start point.  It's all just a bunch of words until we put it to the test.

I've done this experiment so I can tell you what I've seen. You can my word for it or you can run it yourself. If your results differ from mine then we have to go over our procedures and see who botched what. But if you get the same results then you might have some problems with your theory that needs some work.

That's how falsification works and it takes a certain kind of masochism to perform without prejudice because it's essentially actively working to kill your own intellectual property.

Ok, well first of all, go and get a chamber for pressurising and evacuating. Then do the tests.

Go back and read what I've written more carefully. I have performed these tests.

Try and understand what I'm saying.

But high density materials still weigh different. An empty gas cylinder will weigh less than a full one, but no air gets in when it's empty or full. You cannot explain this.

You've just answered your own question.

Stop claiming the same thing over and over. I have already shown you mean times to be wrong.

You do seem mean but you've shown me nothing except bullshit. You did not follow my instructions and you know it.

Quote from: sceptimatic on July 30, 2016, 08:35:44 AM

Quote from: sandmanMike on July 30, 2016, 08:30:42 AM

Quote from: sceptimatic on July 30, 2016, 08:01:58 AM

Not correct. It's still under equilibrium.

Could you explain?

If you allow atmospheric pressure to expand and exit out of a chamber, it will still leave an equal (all around inside) but less pressure inside of that chamber. So therefore anything inside it is simply still a dense object sitting inside under that pressure.

But if you remove the air, then nothing is pushing down on the object to cause weight.  The absense of air pressure would be the absense of weight in ya'lls definition.

Air can only push down on an object pushing INTO it. This is how we measure the weight by man made scale plates.

So, if someone was in space, and they just twitched a muscle, they would be ripped apart because all of their body parts suddenly shot off at light speed in different directions?

There's no such thing as light speed. It's nonsense.

In fictional space you can move all your muscles and you go nowhere. Basically you would be in suspended animation going by how you people see space.
The truth is unknown and never will be by us humans on what is outside of this cell we live in.

Quote from: origamiscienceguy on July 30, 2016, 12:56:26 PM

So, if someone was in space, and they just twitched a muscle, they would be ripped apart because all of their body parts suddenly shot off at light speed in different directions?

There's no such thing as light speed. It's nonsense.

In fictional space you can move all your muscles and you go nowhere. Basically you would be in suspended animation going by how you people see space.
The truth is unknown and never will be by us humans on what is outside of this cell we live in.

Hey,  welcome back scepti,   I'm pleased to see you came back,   I know you don't believe me, but that's not my problem.

If there is no such thing as light speed,  what do you think the speed of light is?

Quote from: sandmanMike on July 30, 2016, 12:54:33 PM

Quote from: sceptimatic on July 30, 2016, 08:35:44 AM

Quote from: sandmanMike on July 30, 2016, 08:30:42 AM

Quote from: sceptimatic on July 30, 2016, 08:01:58 AM

Not correct. It's still under equilibrium.

Could you explain?

If you allow atmospheric pressure to expand and exit out of a chamber, it will still leave an equal (all around inside) but less pressure inside of that chamber. So therefore anything inside it is simply still a dense object sitting inside under that pressure.

But if you remove the air, then nothing is pushing down on the object to cause weight.  The absense of air pressure would be the absense of weight in ya'lls definition.

Air can only push down on an object pushing INTO it. This is how we measure the weight by man made scale plates.

Right, so you agree an object in a vacuum chamber would be weightless and should float.

Quote from: sandmanMike on July 30, 2016, 12:54:33 PM

Quote from: sceptimatic on July 30, 2016, 08:35:44 AM

Quote from: sandmanMike on July 30, 2016, 08:30:42 AM

Quote from: sceptimatic on July 30, 2016, 08:01:58 AM

Not correct. It's still under equilibrium.

Could you explain?

If you allow atmospheric pressure to expand and exit out of a chamber, it will still leave an equal (all around inside) but less pressure inside of that chamber. So therefore anything inside it is simply still a dense object sitting inside under that pressure.

But if you remove the air, then nothing is pushing down on the object to cause weight.  The absense of air pressure would be the absense of weight in ya'lls definition.

Air can only push down on an object pushing INTO it. This is how we measure the weight by man made scale plates.

Get this! Air is a fluid. In a fluid pressure is the same in all directions.
In a fluid the force pushing up on the bottom of an object is almost exactly the same as the force pushing down on the top.
(I said "almost exactly" because air pressure changes slightly as we move up, only about 0.012% per metre)
In any case, the force pushing up on the bottom of an object is always greater than the force on the top of the object.


So, density is important when it comes to an object floating, but pressure is not important, only the change in pressure, which is caused by the density of the fluid.


You can claim that we have close minds as much as you like, but that does not change facts that have been demonstrated for hundreds of years.

It is you that has completely closed you mind to any other ideas.

How come when I get in an airplane and go 30,000 feet in the air, the air pressure is .3 as much as at sea level, yet I weigh the exact same?

Quote from: iWitness on July 30, 2016, 12:58:48 PM

Congratulations! The experiment proves a Bowling Ball is more dense (heavier) than little to no air (i doubt a true vacuum is even possible).

Density does not mean weight.

Not in your indoctrinated law but in reality it is the direct cause of the man made  scale measurement that determines the density against atmospheric resistance to it.

What about baloons? They also have the same amount of air "pushing them down" as everything else.

Yes but the balloon is full of compressed air, so still creates a resistance against air above and is more dense than below.

Or what about a metal stick. If you put it vertically, it weighs the same as horizontally, even though there is much less air above it "pushing it down" when it is vertical.

A metal stick stood erect is pushing up again st the atmosphere by length, so it still pushes away the length of itself of atmosphere.
Laid horizontally is pushed the width of it's entire length against the atmosphere.

To make this easier to grasp. Imagine putting two identical sticks on a white sheet of paper. One horizontal and one vertical.
Now spray the paper and take away both sticks. You have the shapes of both sticks as white on a black back-ground.

Both stick shapes have taken up identical spaces just in different formation.

Quote from: sokarul on July 30, 2016, 01:34:03 PM

Quote from: iWitness on July 30, 2016, 12:58:48 PM

Congratulations! The experiment proves a Bowling Ball is more dense (heavier) than little to no air (i doubt a true vacuum is even possible).

Density does not mean weight.

Not in your indoctrinated law but in reality it is the direct cause of the man made  scale measurement that determines the density against atmospheric resistance to it.

Do you know that I find that a completely meaningless statement? Does anyone else?

How do YOU measure weight? How can we measure anything without using man-made instruments?
By the way, I suppose you know that you cannot measure weight with a balance type "weighing machine", that just compares masses.

Air (or water) pressure cannot possibly cause what we call "weight" simply because air is a fluid.

Yes, it's a much less dense fluid. Water is more dense. Weight is simply a man made measurement by a man made scale using a solid base as leverage to repel/push against atmosphere and measuring the push of anything placed upon that scale plate against that atmosphere to give a reading of what we know as, WEIGHT.

Pressure in a fluid always causes a force at right-angles to the surfaces of any objects in it.

Either by push into atmosphere or by grip of atmosphere upon the surface and sides, against the leverage of the solid ground.

So if we have a horizontal flat sheet the force pressing down on the top surface is balanced by an equal force pressing up on the bottom.

No it's not. The solid floor is a resistant force that stops the push of the plate against the atmosphere above from pushing it further down. A resistance of the actual area and width of the sheet, plus the density of it.

It does not matter how high or low the pressure is the same thing applies, as long as the pressure on the top is the same as the pressure on the bottom. So the pressure does not cause any nett downward force, so does not contribute to weight.

It does matter. the higher the pressure means the higher the squeeze of any object or fluid/gas, meaning the potential for that object/fluid/gas gets squeezed upwards, or floats to our perception.

Now we know from measurements that the air pressure gets lower as we increase in altitude.

Yes, I agree with that.

Intuitively it would seem that this cannot be a very great amount, but it is more than we realise. A helium balloon floats simply because the air pressure pressing up from underneath is slightly greater than the air pressure pushing it down.

Correct. Just remember though that the atmosphere is SQUEEZING the less dense object (helium balloon for instance) UP and will continue to do so until the atmosphere reaches equilibrium, in which case we would see the balloon simply appear to hover or float, but usually would pop due to the balloon losing it's elasticity.

The amount of this lift can easily be calculated. A cubic metre of air (at STP^[1]) weighs 1.225 kg, so the air pressure decreases by 1.225 kg per square metre for each metre increase in altitude. This sounds a lot until it is realised that the normal air pressure is 10,340 kg/m².

So back to our funny cube shaped helium balloon, the total force caused the pressure on the bottom is 1.225 kg more than the force on the top, so there is a nett uplift of 1.225 kg.

Now of course we have to subtract from this the weight of the balloon. If we can neglect the weight of the balloon skin, the weight of the helium would be its density (0.164 kg/m³) times its volume (1 m³), or 0.164 kg.

So a 1 cubic metre helium balloon has a buoyancy of just over 1 kg, less the weight of the balloon structure. 

There's really no need to go into this. This just adds nothing to the understanding.

In the end the shape of the balloon makes no difference and the "lift" is simply the

(density of the air displaced) x (the volume of the object)

In other words Archimedes Principle.

So, certainly density comes into working out buoyancy,

but pressure cannot cause weight, because the forces caused by pressure act equally in all directions.

[1] STP is short for Standard Pressure and Temperature, ie sea level,  etc.

Shape simply makes for a better uplift.

Quote from: sceptimatic on July 31, 2016, 02:46:39 AM

Quote from: origamiscienceguy on July 30, 2016, 12:56:26 PM

So, if someone was in space, and they just twitched a muscle, they would be ripped apart because all of their body parts suddenly shot off at light speed in different directions?

There's no such thing as light speed. It's nonsense.

In fictional space you can move all your muscles and you go nowhere. Basically you would be in suspended animation going by how you people see space.
The truth is unknown and never will be by us humans on what is outside of this cell we live in.

Hey,  welcome back scepti,   I'm pleased to see you came back,   I know you don't believe me, but that's not my problem.

If there is no such thing as light speed,  what do you think the speed of light is?

Simply vibration and frequency.

Basically anything we use to transmit is done instantly to reach the distance that the energy applied allows it to.
Newtons cradle is a perfect example of what I'm taking about. It shows the basic simplicity of what's happening with everything.

Quote from: sceptimatic on July 31, 2016, 02:42:03 AM

Quote from: sandmanMike on July 30, 2016, 12:54:33 PM

Quote from: sceptimatic on July 30, 2016, 08:35:44 AM

Quote from: sandmanMike on July 30, 2016, 08:30:42 AM

Quote from: sceptimatic on July 30, 2016, 08:01:58 AM

Not correct. It's still under equilibrium.

Could you explain?

If you allow atmospheric pressure to expand and exit out of a chamber, it will still leave an equal (all around inside) but less pressure inside of that chamber. So therefore anything inside it is simply still a dense object sitting inside under that pressure.

But if you remove the air, then nothing is pushing down on the object to cause weight.  The absense of air pressure would be the absense of weight in ya'lls definition.

Air can only push down on an object pushing INTO it. This is how we measure the weight by man made scale plates.

Right, so you agree an object in a vacuum chamber would be weightless and should float.

No I don't.

Get this! Air is a fluid. In a fluid pressure is the same in all directions.

Sort of, yeah.

In a fluid the force pushing up on the bottom of an object is almost exactly the same as the force pushing down on the top.
(I said "almost exactly" because air pressure changes slightly as we move up, only about 0.012% per metre)
In any case, the force pushing up on the bottom of an object is always greater than the force on the top of the object.

No. The object itself is always greater pushing up than the force on top of the object. You need to understand this.

This is why an object less dense than air floats in air, or an object less dense than water floats in water - mind you old Archimedes worked this out first!

Ask yourself how it becomes less dense. See if you can figure it out.

So, density is important when it comes to an object floating, but pressure is not important, only the change in pressure, which is caused by the density of the fluid.

So air pressure (or water pressure) simply cannot cause an objects weight!

Atmospheric pressure is the absolute direct cause of a persons density being measured against a scale plate to record what we know as a measurement of weight.

You can claim that we have close minds as much as you like, but that does not change facts that have been demonstrated for hundreds of years.

It is you that has completely closed you mind to any other ideas.

I don't care what's been demonstrated. It's wrong.
Atmospheric pressure is 100% correct in everything we do on Earth, inside this cell.

There's no magical gravity or any of the other gunk. It's complete and utter nonsense that is turned into make believe by story telling sci-fi writers, to this very day.

Quote from: crutonius on July 30, 2016, 12:31:07 PM

Quote from: sceptimatic on July 30, 2016, 12:05:47 PM

Quote from: crutonius on July 30, 2016, 10:24:18 AM

Quote from: sceptimatic on July 30, 2016, 09:10:26 AM

Quote from: crutonius on July 30, 2016, 08:56:51 AM

Quote from: sceptimatic on July 30, 2016, 08:35:44 AM

Quote from: sandmanMike on July 30, 2016, 08:30:42 AM

Quote from: sceptimatic on July 30, 2016, 08:01:58 AM

Not correct. It's still under equilibrium.

Could you explain?

If you allow atmospheric pressure to expand and exit out of a chamber, it will still leave an equal (all around inside) but less pressure inside of that chamber. So therefore anything inside it is simply still a dense object sitting inside under that pressure.

I would like some clarification on this as well. It seems like a pretty simple thing to test.

Get a vacuum chamber.

Put a kitchen scale in it.

Put a weight on the scale.

Evacuate the air and then observe.

Yep, as long as the test is done legitimately and not a con job like sokarul tried.

That's kind of the point. These discussions are only a start point.  It's all just a bunch of words until we put it to the test.

I've done this experiment so I can tell you what I've seen. You can my word for it or you can run it yourself. If your results differ from mine then we have to go over our procedures and see who botched what. But if you get the same results then you might have some problems with your theory that needs some work.

That's how falsification works and it takes a certain kind of masochism to perform without prejudice because it's essentially actively working to kill your own intellectual property.

Ok, well first of all, go and get a chamber for pressurising and evacuating. Then do the tests.

Go back and read what I've written more carefully. I have performed these tests.

Try and understand what I'm saying.

Adorable. You have your own pretend physics.

Alright. Have it your way. You just keep on believing that if it makes you feel better.

Just take things easy when you actually have to build things affected by gravity. You might get embarrassed.