If I jump in the air why doesn't the ground move @ 1000MPH?

Quote from: Scintific Method on January 08, 2014, 05:46:53 PM

Quote from: sceptimatic on January 08, 2014, 05:41:53 PM

Ok, I'll take your word for it.

Much appreciated, but it would be even better if you understood it too.

I don't agree with it, I just said I'll take your word for it, because it's easier than getting into an argument over it where everyone jumps in and I say something back and then the banning orders start on me.

I wasn't asking you to agree, just to understand. Whether you do or not is up to you, of course.

Quote from: BJ1234 on January 08, 2014, 05:56:02 PM

Also, how do you explain that a table cloth pulled sufficiently fast will leave everything standing? 

A table cloth pulled at speed, creates a low pressure under the items that is immediately filled as you yank it, ensuring that your items sort of minutely levitate for an instant, allowing you to cleanly pull the full cloth if done correctly.

All I can do, is promise you that I am 100% correct in what I'm telling you, in that your gravity and inertia are simple the results of atmospheric pressure in the different forms it works in, as in high and low pressure.

Again a totally wrong interpretation of what actually happens!  There is no "levitation" of the objects on the tablecloth. Why?  Because the only force acting in a vertical direction is gravity, which obviously doesn't change.

The real answer is that by pulling the tablecloth sharply, the inertia of the objects on the cloth is enough to overcome the coefficient of friction between the objects and the tablecloth.

And you need to be careful making promises that are so easily broken by other people on your behalf.  Neither gravity nor inertia are affected by atmospheric pressure.  Both act identically in a vacuum.

Nah, too complicated.  The table cloth is just pulled out too quickly for the items on the cloth to react.  Think I'm getting the hang of this simple explanation stuff.  What do you think, Scepti?

Quote from: BJ1234 on January 08, 2014, 05:56:02 PM

So the void is created by the air moving back, and this is what pushes you back, yet when the void gets filled up, the air doesn't push you forward at all?  Why would the air be able to push you in one direction, but not in the other?

The air being pushed back, compresses against you, forcing you back and as it does so, it creates a LOWER pressure at the very front that is immediately filled all the time the bus is accelerating. As soon as the bus stops accelerating, the compressed air equalizes which you feel as the weight coming off of you.

It's much simpler, scepti.  When a bus accelerates, it pushes on you, and you feel it.  When it stops accelerating, it stops pushing you, cause you're just moving along with it.

Once the bus moves, the back of the bus will have the air forced against it but in a pressurised way, not as in wind, leaving a low pressure at the very front which will be also filled. Think of it like the bus being filled with sponges and as it accelerates it squashes the sponges to the back, then as it does that, you slip in a load of sponges very quickly into the gap at the front where the pressure has been relieved. (low pressure)

when you say the air forced against it? Do you mean the surface of the back of the bus would push the air at the back into the air at the front which compresses it?

]The air will simply compress, immediately.

you mean when the bus slows down the air at the front of the bus will collide with the bus and the air towards the back will collide with the air in front of it because it is now moving faster than the bus?

I think that would hardly be noticeable and would basically more rely on the mass of the actual bus itself, although naturally there would be more volume of air inside of it.

I was talking hypothetically. So the more air the bus needs to move the more force it would need in order to shift the air. You could have the same size bus but pressurised air inside if it makes it easier to think of.

Quote from: sceptimatic on January 08, 2014, 05:09:44 PM

Quote from: sokarul on January 08, 2014, 05:06:15 PM

Quote from: sceptimatic on January 08, 2014, 05:03:14 PM

Quote from: sokarul on January 08, 2014, 04:56:19 PM

You greatly over estimate atmospheric pressure. It takes a fast wind to move people.
#ws" class="bbc_link" target="_blank" rel="noopener noreferrer">Walkin' in the Wind: People blown over in streets as Storm Ivar hits Norway

Also, why were you unable to address my claims that inertia would be responsible for air moving inside your bus argument? If a bus turned and the air inside caused a person to be pressed against the wall, it would be because of the air's inertia.

You do not understand atmospheric pressure in its entirety. I know you will argue that you do, but you simply do not and I know this by the fact that you are using HORIZONTAL wind pressures like this to prove something and it's not the whole story at all.

Here's a clue:
You borrow something and you must pay it back. What is it that you can borrow but must be paid back to make things equal?

Oh and what do you mean by the air inertia. What does that even mean?

Do you die a little inside every time people show you to be wrong?

No. I would accept it, but in this case, I am not wrong, I am 100% correct in what I'm saying, it's just a shame that people can't apply their mind to what I'm saying, because they are too absorbed with spouting, "he's a loon and he can't do math."
You know, silly stuff like that.

Maybe you should take the hint.
Then you won't have to attack my horizontal wind pressure argument when you use horizontal air pressure in a bus to move people horizontally.

I wasn't attacking it, I was merely telling you that you are not looking at it in its entirety.

Again a totally wrong interpretation of what actually happens!  There is no "levitation" of the objects on the tablecloth. Why?  Because the only force acting in a vertical direction is gravity, which obviously doesn't change.

Ok, let's see if I can maybe put this another way. Imagine you have a sheet sander on the table and you decide to sand it. You sort of feel it levitate, right, even though you know it's sanding the table. You also know how much easier it is to push over the table as opposed to doing it when turned off. It's basically friction and the speed of friction which is heat in any form.
You also know that heat agitates molecules and agitated molecules are expanding. This is what is happening under your items on the table by the speedy pull of that table cloth and it creates a SORT of levitation effect.

The real answer is that by pulling the tablecloth sharply, the inertia of the objects on the cloth is enough to overcome the coefficient of friction between the objects and the tablecloth.

Hang onto that if you want but there is no such thing as inertia.

And you need to be careful making promises that are so easily broken by other people on your behalf.  Neither gravity nor inertia are affected by atmospheric pressure.  Both act identically in a vacuum.

Nothing can act in a vacuum. If you mean a partially evacuated chamber then yes, things would act differently but it's because of the lack of pressure and friction and has nothing to do with inertia or gravity as they do not exist as any force except to be named as a reason for the happenings that atmospheric pressure perfectly explains and can be tested.

Nah, too complicated.  The table cloth is just pulled out too quickly for the items on the cloth to react.  Think I'm getting the hang of this simple explanation stuff.  What do you think, Scepti?

In a way you are correct because it is actually the speed which is the key to anything, but it's by agitation of matter/molecules that determines pressures, which is the key to everything from wind to everything that happens on earth no matter what it is.
No fictional forces are needed like gravity and this inertia thought. It's just not required, but it's needed to make space a reality, which it's not.

Quote from: sceptimatic on January 08, 2014, 06:04:54 PM

Quote from: BJ1234 on January 08, 2014, 05:56:02 PM

So the void is created by the air moving back, and this is what pushes you back, yet when the void gets filled up, the air doesn't push you forward at all?  Why would the air be able to push you in one direction, but not in the other?

The air being pushed back, compresses against you, forcing you back and as it does so, it creates a LOWER pressure at the very front that is immediately filled all the time the bus is accelerating. As soon as the bus stops accelerating, the compressed air equalizes which you feel as the weight coming off of you.

It's much simpler, scepti.  When a bus accelerates, it pushes on you, and you feel it.  When it stops accelerating, it stops pushing you, cause you're just moving along with it.

To disprove this, all you need to do is sit on that bus with a cup of water and as it accelerates forward, tell me which way the water swills out.
Wear waterproof trousers, because it's coming at you not being pushed forward.

It's much simpler, scepti.  When a bus accelerates, it pushes on you, and you feel it.  When it stops accelerating, it stops pushing you, cause you're just moving along with it.

To disprove this, all you need to do is sit on that bus with a cup of water and as it accelerates forward, tell me which way the water swills out.
Wear waterproof trousers, because it's coming at you not being pushed forward.
[/quote]

if I sit on a bus and the bus moves forwards the water comes out backwards. the same way it comes out if I stand and push a cup forward.

Because it resists being moved forward with the cup.

The same way air resists being moved forward by the back of the bus.

when you say the air forced against it? Do you mean the surface of the back of the bus would push the air at the back into the air at the front which compresses it?

Yes! When the bus accelerates, it sort of immediately leaves the air at a standing start and the back of the bus is driving into the air....but the void that is left at the front of the bus is immediately filled creating the push or higher pressure onto the people on that bus which you feel as a force on you as long as the bus accelerates.

you mean when the bus slows down the air at the front of the bus will collide with the bus and the air towards the back will collide with the air in front of it because it is now moving faster than the bus?

When the bus slows down.let's say an emergency stop.
As soon as the brake is applied, the opposite happens, except more violently. Let's assume the bus was doing 50 mph, so we know that the air inside of it is moving at 50 mph which is fine as long as the bus is at that constant speed. If the driver slams his foot on the brake, you get a 50mph force of pressure...not steady wind....pressure, there is a massive difference, because during that violent emergency stop...not only has the air just went forward...it has done so whilst creating a low pressure which is filled constantly for the duration of that stop. It's a massive pressure build up and you feel it act violently on your back forcing you forward....
As soon as that bus stops dead...the air pressure quickly equalizes, which means it expels the excess pressure from the bus that you feel as a jolt backwards again.
Can you see what I'm saying?

I was talking hypothetically. So the more air the bus needs to move the more force it would need in order to shift the air. You could have the same size bus but pressurized air inside if it makes it easier to think of.

I'm not quite sure what you are getting at with this question. It appears to be a kind of question designed to trip me up for some reason. If I'm wrong the fair enough.

if I sit on a bus and the bus moves forwards the water comes out backwards. the same way it comes out if I stand and push a cup forward.

Because it resists being moved forward with the cup.

The same way air resists being moved forward by the back of the bus.

Can you elaborate on this, I'm not quite sure what you are getting at. I understand the water bit but not what you are getting at with the cup.

Quote from: Spank86 on January 09, 2014, 02:26:44 AM

if I sit on a bus and the bus moves forwards the water comes out backwards. the same way it comes out if I stand and push a cup forward.

Because it resists being moved forward with the cup.

The same way air resists being moved forward by the back of the bus.

Can you elaborate on this, I'm not quite sure what you are getting at. I understand the water bit but not what you are getting at with the cup.

If you use your hand to move a cup of water forward the water (and cup) will resist this and want to stay still.

The same occurs if you use a bus to move the cup.

Equally the same tries to happen if you put your hand over the cup, you'll feel the water pushing against the part of the hand at the back of the cup.


Essentially back of the cup tries to move into space already occupied by water, this water cannot go forward because there's more water in the way and eventually there's the front of the cup so it goes upwards and spears to spill over the rear of the cup (it's actually the rear of the cup moving under the water and giving it a path of least resistance downwards).

Quote from: sceptimatic on January 09, 2014, 02:42:24 AM

Quote from: Spank86 on January 09, 2014, 02:26:44 AM

if I sit on a bus and the bus moves forwards the water comes out backwards. the same way it comes out if I stand and push a cup forward.

Because it resists being moved forward with the cup.

The same way air resists being moved forward by the back of the bus.

Can you elaborate on this, I'm not quite sure what you are getting at. I understand the water bit but not what you are getting at with the cup.

If you use your hand to move a cup of water forward the water (and cup) will resist this and want to stay still.

The same occurs if you use a bus to move the cup.

Equally the same tries to happen if you put your hand over the cup, you'll feel the water pushing against the part of the hand at the back of the cup.


Essentially back of the cup tries to move into space already occupied by water, this water cannot go forward because there's more water in the way and eventually there's the front of the cup so it goes upwards and spears to spill over the rear of the cup (it's actually the rear of the cup moving under the water and giving it a path of least resistance downwards).

The cup is in your hand and as you are pushed back you drag the cup with you. You can counter balance it by pushing your hand forward as you go back if you are quick enough and a re ready for the acceleration.

If you were to place that cup on a table on that bus and it accelerated, the air pressure will still force the cup over and over you.
Look, I know you are hanging onto inertia and gravity for dear life and fair enough. Just put your mind to what I'm saying and try to put gravity and inertia to the side whilst you do it and you may think more clearly.
I know I am 100% correct on this. I really do.

Quote from: Spank86 on January 09, 2014, 03:20:12 AM

Quote from: sceptimatic on January 09, 2014, 02:42:24 AM

Quote from: Spank86 on January 09, 2014, 02:26:44 AM

if I sit on a bus and the bus moves forwards the water comes out backwards. the same way it comes out if I stand and push a cup forward.

Because it resists being moved forward with the cup.

The same way air resists being moved forward by the back of the bus.

Can you elaborate on this, I'm not quite sure what you are getting at. I understand the water bit but not what you are getting at with the cup.

If you use your hand to move a cup of water forward the water (and cup) will resist this and want to stay still.

The same occurs if you use a bus to move the cup.

Equally the same tries to happen if you put your hand over the cup, you'll feel the water pushing against the part of the hand at the back of the cup.


Essentially back of the cup tries to move into space already occupied by water, this water cannot go forward because there's more water in the way and eventually there's the front of the cup so it goes upwards and spears to spill over the rear of the cup (it's actually the rear of the cup moving under the water and giving it a path of least resistance downwards).

The cup is in your hand and as you are pushed back you drag the cup with you. You can counter balance it by pushing your hand forward as you go back if you are quick enough and a re ready for the acceleration.

If you were to place that cup on a table on that bus and it accelerated, the air pressure will still force the cup over and over you.
Look, I know you are hanging onto inertia and gravity for dear life and fair enough. Just put your mind to what I'm saying and try to put gravity and inertia to the side whilst you do it and you may think more clearly.
I know I am 100% correct on this. I really do.

In your theory WHY does the air resist moving when the cup is forced into it and conversely why does the water NOT resist movement without air pressure?

Also why do you feel the same phenomenon of the abck of your seat pushing you forward in both an enclosed and open top bus.

In your theory WHY does the air resist moving when the cup is forced into it and conversely why does the water NOT resist movement without air pressure?

Can you clarify what you're getting at here.

Also why do you feel the same phenomenon of the abck of your seat pushing you forward in both an enclosed and open top bus.

You don't feel the back of your seat pushing into you, your body is pushing your back into it. The seat is fixed, how can it push into you. Think about it.

Quote from: Spank86 on January 09, 2014, 05:07:37 AM

In your theory WHY does the air resist moving when the cup is forced into it and conversely why does the water NOT resist movement without air pressure?

Can you clarify what you're getting at here.

Quote from: Spank86 on January 09, 2014, 05:07:37 AM

Also why do you feel the same phenomenon of the abck of your seat pushing you forward in both an enclosed and open top bus.

You don't feel the back of your seat pushing into you, your body is pushing your back into it. The seat is fixed, how can it push into you. Think about it.

Because the bus moved forward, the seat is attached to the bus, therefore, the seat moved forward.

Quote from: Spank86 on January 09, 2014, 05:07:37 AM

In your theory WHY does the air resist moving when the cup is forced into it and conversely why does the water NOT resist movement without air pressure?

Can you clarify what you're getting at here.

Well you're saying that the air resists being pushed about. It must resist being moved about or it wouldn't exert any force on objects that move through it.

You then don't seem to believe that water or anything else also resists movement and requires a force to move it.

You don't feel the back of your seat pushing into you, your body is pushing your back into it. The seat is fixed, how can it push into you. Think about it.

the seat is fixed...to a moving bus. so the seat is moving with the bus. You are stationary until moved. The same as the air at the back of the bus is stationary until moved by the back.

Quote from: sceptimatic on January 09, 2014, 05:22:04 AM

Quote from: Spank86 on January 09, 2014, 05:07:37 AM

In your theory WHY does the air resist moving when the cup is forced into it and conversely why does the water NOT resist movement without air pressure?

Can you clarify what you're getting at here.

Quote from: Spank86 on January 09, 2014, 05:07:37 AM

Also why do you feel the same phenomenon of the abck of your seat pushing you forward in both an enclosed and open top bus.

You don't feel the back of your seat pushing into you, your body is pushing your back into it. The seat is fixed, how can it push into you. Think about it.

Because the bus moved forward, the seat is attached to the bus, therefore, the seat moved forward.

Of course, but it's moving as part of the bus it's not pushing into you and that should be evident and I cannot fathom out why you can't see this.

But if it moved forward with the bus, why wouldn't it push into your back?

Well you're saying that the air resists being pushed about. It must resist being moved about or it wouldn't exert any force on objects that move through it.

It does resist being moved about. It compresses and expands as I've said.

You then don't seem to believe that water or anything else also resists movement and requires a force to move it.

When have I said that? Have you even read any of this topic?

the seat is fixed...to a moving bus. so the seat is moving with the bus. You are stationary until moved. The same as the air at the back of the bus is stationary until moved by the back.

No...it doesn't work like that. If the bus accelerates then so does the seat at the same speed. Not so with the air as the air cannot grip like a bolted seat, so the back of the bus crashes into the air all the way up the bus to leave a low pressure due to compression that immediately gets filled, creating a higher pressure inside the bus than outside pressure, marginally and depending on acceleration, depends on the force of compression into more pressure against you.

But if it moved forward with the bus, why wouldn't it push into your back?

Because you are part of that seat and all that happens is the air pressure pushes the FRONT of your body and pushes you back against the seat, not the other way round.

The only way a seat would push into your back is if it was unbolted and you were stood just in front of it with your back to it and the bus was accelerating in reverse.

I'm lost.
Let's put a kid on a skateboard in the middle of a stopped bus.
Everybody is at rest.
The bus accelerates. The kid would stay at rest, go forward or backwards ?

I'm lost.
Let's put a kid on a skateboard in the middle of a stopped bus.
Everybody is at rest.
The bus accelerates. The kid would stay at rest, go forward or backwards ?

In reality, the kid would be flung backwards and his skateboard propelled forwards by the friction of his feet, due to the air pressure build up on him.
If he could stick to his skateboard and balance himself, he and his skateboard would be propelled backwards because his body will take the impact of the air pressure being compressed against him.

Quote from: BJ1234 on January 09, 2014, 05:49:12 AM

But if it moved forward with the bus, why wouldn't it push into your back?

Because you are part of that seat and all that happens is the air pressure pushes the FRONT of your body and pushes you back against the seat, not the other way round.

The only way a seat would push into your back is if it was unbolted and you were stood just in front of it with your back to it and the bus was accelerating in reverse.

Is this distinction relevant? Saying that a seat attached to a bus is pushing you, or you are pushing on the bus seems to be of no consequence. I know you cringe when you hear about math but it's simple addition. We could say it's the seat but to make you feel better we can just say bus and threat the bus and the seat as one entity since they are attached to each other. So to illustrate the point here I will just say bus+seat to make it clear that I mean the bus and the seat.

All things considered, before anything starts happening everyone (you and the bus+seat) is at rest.

When things start moving the important thing to consider is what that acceleration is relative to something and before they start moving everyone is at rest relative to the earth.

So, as things start moving the bus+seat starts off at about 5 m/s/s while you (not being attached to the bus) are still at rest relative to the earth. You have not moved (relative to the earth) until the seat meets your back. So (relative to the earth) it couldn't be you pushing the seat because (relative to the earth) the only object moving is the bus+seat.

While the bus continues to accelerate it's inertia is also increasing and still pushing into your back. Once it stop accelerating and reaches a steady speed, you become at rest relative to the bus+seat instead of at rest relative to the earth.

So the kids is propelled backwards to the rear of the bus. If we open the rear door, the kid will get out (he's quite good, he is still on the skate).
Will he be still moving backwards outside?

Quote from: sceptimatic on January 09, 2014, 05:58:35 AM

Quote from: BJ1234 on January 09, 2014, 05:49:12 AM

But if it moved forward with the bus, why wouldn't it push into your back?

Because you are part of that seat and all that happens is the air pressure pushes the FRONT of your body and pushes you back against the seat, not the other way round.

The only way a seat would push into your back is if it was unbolted and you were stood just in front of it with your back to it and the bus was accelerating in reverse.

Is this distinction relevant? Saying that a seat attached to a bus is pushing you, or you are pushing on the bus seems to be of no consequence. I know you cringe when you hear about math but it's simple addition. We could say it's the seat but to make you feel better we can just say bus and threat the bus and the seat as one entity since they are attached to each other. So to illustrate the point here I will just say bus+seat to make it clear that I mean the bus and the seat.

All things considered, before anything starts happening everyone (you and the bus+seat) is at rest.

When things start moving the important thing to consider is what that acceleration is relative to something and before they start moving everyone is at rest relative to the earth.

So, as things start moving the bus+seat starts off at about 5 m/s/s while you (not being attached to the bus) are still at rest relative to the earth. You have not moved (relative to the earth) until the seat meets your back. So (relative to the earth) it couldn't be you pushing the seat because (relative to the earth) the only object moving is the bus+seat.

While the bus continues to accelerate it's inertia is also increasing and still pushing into your back. Once it stop accelerating and reaches a steady speed, you become at rest relative to the bus+seat instead of at rest relative to the earth.

All I can say to all that is, they done one hell of a job on you.
Ok, tell me this.
If you are sat on the same bus  sat on a sort of school like plastic chair with metal legs, not bolted down. The bus accelerates forward and you go tipping over backwards. Tell me how that seat managed to push you in the back.

So the kids is propelled backwards to the rear of the bus. If we open the rear door, the kid will get out (he's quite good, he is still on the skate).
Will he be still moving backwards outside?

If the bus was going at a decent accelerating speed then he would skate out of the back, hit the road and would be following the bus with his back to it at a slower speed.
For instance. If the bus has accelerated to 50 mph by the time the kid went out the back and the kid left the back of the bus going at 10 mph, then he would land and assuming he could stay on his board, he would be following the bus at approx 40 mph for a second or two before he gradually slowed down.

Quote from: rottingroom on January 09, 2014, 06:14:05 AM

Quote from: sceptimatic on January 09, 2014, 05:58:35 AM

Quote from: BJ1234 on January 09, 2014, 05:49:12 AM

But if it moved forward with the bus, why wouldn't it push into your back?

Because you are part of that seat and all that happens is the air pressure pushes the FRONT of your body and pushes you back against the seat, not the other way round.

The only way a seat would push into your back is if it was unbolted and you were stood just in front of it with your back to it and the bus was accelerating in reverse.

Is this distinction relevant? Saying that a seat attached to a bus is pushing you, or you are pushing on the bus seems to be of no consequence. I know you cringe when you hear about math but it's simple addition. We could say it's the seat but to make you feel better we can just say bus and threat the bus and the seat as one entity since they are attached to each other. So to illustrate the point here I will just say bus+seat to make it clear that I mean the bus and the seat.

All things considered, before anything starts happening everyone (you and the bus+seat) is at rest.

When things start moving the important thing to consider is what that acceleration is relative to something and before they start moving everyone is at rest relative to the earth.

So, as things start moving the bus+seat starts off at about 5 m/s/s while you (not being attached to the bus) are still at rest relative to the earth. You have not moved (relative to the earth) until the seat meets your back. So (relative to the earth) it couldn't be you pushing the seat because (relative to the earth) the only object moving is the bus+seat.

While the bus continues to accelerate it's inertia is also increasing and still pushing into your back. Once it stop accelerating and reaches a steady speed, you become at rest relative to the bus+seat instead of at rest relative to the earth.

All I can say to all that is, they done one hell of a job on you.
Ok, tell me this.
If you are sat on the same bus  sat on a sort of school like plastic chair with metal legs, not bolted down. The bus accelerates forward and you go tipping over backwards. Tell me how that seat managed to push you in the back.

Well there is a few questions here. On the original bus with attached seats, those seats are attached by sturdy bolts, in that case we can consider them to be one entity in terms of their motion relative to the earth. Bolts are very good at putting things together and keeping them attached to each other.

Gravity, like bolts can keep things attached to each other but certainly not as well as bolts. Depending on the weight of the metal chair you just brought up, the amount of force that seat would push on you would depend on how long it would take before the acceleration of the bus is high enough such that gravity could no longer keep the metal seat attached to the bus. Your weight on the seat would also help keep the metal seat attached.

If the seat was extremely heavy, it might fare pretty well. If it were a light plastic chair it wouldn't do as well. During the moments before it topples over (in other words: it is still attached to the bus by gravity). That seat and the bus are pushing on you together as one entity. Once the acceleration is high enough such that it is not attached to the bus then you and the seat will topple over before meeting the ground.

Once you and the seat are on the floor you are now once again attached to the bus because gravity is keeping you attached.

So, if it's hitting me in the back, how can I topple over backwards?
If what you are saying is correct, than that seat pushing onto my back, should topple me over forwards but that doesn't happen and for good reason. It's because air pressure is at work, not inertia or gravity.