Is Motion possible without Friction?

[Blinky McSquinty]

Ah, wings don't bend?

Again, there is no accelaration without friction. None.

I tried to explain simple classical mechanics, and you fail to grasp Newton's third law. For whatever reason your mind is closed to this method of understanding. It would be a waste of time to continue further with you.

[Nakojo]

Wow.

No need to get up on your high horse, blinky.
It's not nice, as you may understand better reading the rest of my reply...

I tried dumbing it down for you in the rocket example (friction between the expanding gasses and the exhaust) but apparently your grasp of the matter extends no further than standard high school curriculum. Don't blame me for applying it, buddy.

Fwiw, the third law is an extrapolation of the first, as I had hoped my initial post would have illustrated.
Shame it not only passed you by but even more so that you react which such disdain.

Oh, and good luck moving an object with zero friction.

[qczhao]

Ah, wings don't bend?

Again, there is no accelaration without friction. None.

Sorry but this is incorrect. Just taking the solar system as an example, since we can consider space to have zero friction since it's a vacuum: the planets orbit the sun, orbital motion requires objects to be constantly accelerating.

[Nakojo]

Gravitational pull, as addressed in my initial post.

The quote merely addresses blinky's reply.

[qczhao]

Sorry I read your initial post again and I don't see where you have addressed gravitational pull?

At any rate, I believe your other explanations are wrong as well. I'm addressing your points in line below.

In a vacuum it's slightly different, but it's still all about friction.

There can be no friction in a vacuum because the definition of a vacuum is a space in which there are no particles. Without particles to rub past each other, there can be no friction.

The heated gas expands the exhaust, this tries to return to it's original shape -molecular bindings and cooling effect by it's surroundings-, thereby creating friction (between the gasses and the exhaust).
As the rocket meets no environmental friction, this is enough for thrust.
Where else are the expanding gasses and rocket going to go?

Friction is not the root cause for molecular bindings. The heated gas tends to expand because you are increasing its internal energy (by heating it), this means that each molecule of gas contains more kinetic energy which means it collides more frequently with the surrounding molecules, thus forcing the average distance between particles to increase to maintain equilibrium. If you contained the gas instead of allowing it to expand freely, you would get a proportional increase in pressure.

Anyway, in a rocket exhaust, the expanded gas is allowed to go only in one direction (out the exhaust of the rocket). Therefore Newton's 3rd Law tells us the reaction force must propel the rocket in the other direction.

Not unlike a football, it's not the kick that makes the ball travel, the kick dents the ball.
The ball wanting to return to it's natural form (pressure) is the only reason it travels (it can't do so in the same spot, as the foot carries more kinetic energy -try kicking a cannon ball-).

The cannon ball travels far less than the football because of its mass. KE = 0.5 * mass * velocity^2. Therefore, if you have a cannon ball that weights 5kg versus a 0.125kg football (I looked up the weights), the cannonball is actually 40 times heavier, and so you can expect the velocity to be decreased by approx 6 times.

The ball itself travels because when you hit it with your foot you are transferring kinetic energy to the ball. Or, an equally valid way of looking at it would be that your foot exerts a force on the the ball, and a force results in an acceleration (Newton's 2nd Law). Whilst the ball is in contact with your foot, Newton's 3rd Law would be involved also, which says that the force exerted on your foot by the ball would the same as that exerted on the ball by your foot. You would find that your foot would decelerate during the impact phase with the ball.

Curiously (or perhaps not ), the loss in kinetic energy of your foot would be equal to the gain in kinetic energy of the ball.


Consider a sailing boat, the wind just 'bends' the sail.
The sail trying to return to it's original shape makes the boat move.

Unfortunately, I don't think this is the right way to think about this. The sail (and in this case I am thinking of the most basic, parachute type sails) provides a surface area across which a pressure differential can act. On the side of the wind, we have high pressure, on the opposite side of the sail, we have low pressure. Force = Pressure x Area, therefore we have a force. Once we get into more modern sail designs (like for example on a wind-surfing board), there are also other aerodynamic effects at play which enhance the pressure differential effect once the craft starts moving.

[Nakojo]

Sorry I read your initial post again and I don't see where you have addressed gravitational pull?

At any rate, I believe your other explanations are wrong as well. I'm addressing your points in line below.

In a vacuum it's slightly different, but it's still all about friction.

There can be no friction in a vacuum because the definition of a vacuum is a space in which there are no particles. Without particles to rub past each other, there can be no friction.

As there can be no movement without particles rubbing against each other - friction. Be they internal or environmental. In an absolute vacuum, there is no rocket. The absence of particles implies absence of mass, surely.

The heated gas expands the exhaust, this tries to return to it's original shape -molecular bindings and cooling effect by it's surroundings-, thereby creating friction (between the gasses and the exhaust).
As the rocket meets no environmental friction, this is enough for thrust.
Where else are the expanding gasses and rocket going to go?

Friction is not the root cause for molecular bindings. The heated gas tends to expand because you are increasing its internal energy (by heating it), this means that each molecule of gas contains more kinetic energy which means it collides more frequently with the surrounding molecules, thus forcing the average distance between particles to increase to maintain equilibrium. If you contained the gas instead of allowing it to expand freely, you would get a proportional increase in pressure.

Anyway, in a rocket exhaust, the expanded gas is allowed to go only in one direction (out the exhaust of the rocket). Therefore Newton's 3rd Law tells us the reaction force must propel the rocket in the other direction.

I'm not disputing the 3rd law, I'm elaborating on it. Without the molecular binding (and friction) of the exhaust, the gasses would expand circularly. The exhaust 'pushing back', is what causes the propulsion, the directional force of the expanded gasses, so you like. Without that friction, there would be no acceleration (well, marginal, as it will be affected by the expanding gasses anyhow - again, molecular friction).

Not unlike a football, it's not the kick that makes the ball travel, the kick dents the ball.
The ball wanting to return to it's natural form (pressure) is the only reason it travels (it can't do so in the same spot, as the foot carries more kinetic energy -try kicking a cannon ball-).

The cannon ball travels far less than the football because of its mass. KE = 0.5 * mass * velocity^2. Therefore, if you have a cannon ball that weights 5kg versus a 0.125kg football (I looked up the weights), the cannonball is actually 40 times heavier, and so you can expect the velocity to be decreased by approx 6 times.

The ball itself travels because when you hit it with your foot you are transferring kinetic energy to the ball. Or, an equally valid way of looking at it would be that your foot exerts a force on the the ball, and a force results in an acceleration (Newton's 2nd Law). Whilst the ball is in contact with your foot, Newton's 3rd Law would be involved also, which says that the force exerted on your foot by the ball would the same as that exerted on the ball by your foot. You would find that your foot would decelerate during the impact phase with the ball.

Curiously (or perhaps not ), the loss in kinetic energy of your foot would be equal to the gain in kinetic energy of the ball.

Again, this does not contradict my statements. Without the object carrying more kinetic energy being displaced (much), the kinetic energy of the 'lesser' object will move. Action, reaction, right? But why? Friction. Without friction, there would be no transform of energy. The foot would simply travel through the ball.

Consider a sailing boat, the wind just 'bends' the sail.
The sail trying to return to it's original shape makes the boat move.

Unfortunately, I don't think this is the right way to think about this. The sail (and in this case I am thinking of the most basic, parachute type sails) provides a surface area across which a pressure differential can act. On the side of the wind, we have high pressure, on the opposite side of the sail, we have low pressure. Force = Pressure x Area, therefore we have a force. Once we get into more modern sail designs (like for example on a wind-surfing board), there are also other aerodynamic effects at play which enhance the pressure differential effect once the craft starts moving.

Same.
Only the frictional forces of the sail v those of the wind (the environmental gasses crashing into the sail) 'create' all this.
I'm talking pure basics here and have done nothing but apply these laws.

Gravitational pull was addressed -not elaborated on- in my post's conclusion:

Back to OP: yes, motion is possible without friction, acceleration however is not (ignoring gravitatitional pull from other objects).

Odd how nobody disputes the F1 example, while the principle is exactly the same.
Or how people declare statements incorrect while they are in no way contrary to the arguments brought forward, supposedly discrediting said statements.

Quoting and applying laws is one thing, understanding them is quite something else, it appears.

I'll make it as simple as I can: movement (or rather acceleration) is the result of object-particles crashing into environmental-particles. Friction. All other arguments brought forward are merely an elaboration on this principle.

[moby]

May be too simple a statement, but without friction, would everything not be moving?

[Nakojo]

May be too simple a statement, but without friction, would everything not be moving?

Yes, it would, but then we wouldn't know (significant) form or mass either.

Only free particles.

And even that's up for debate looked at closely...

[moby]

May be too simple a statement, but without friction, would everything not be moving?

Yes, it would, but then we wouldn't really know (significant) form or mass either.

Only free particles.

So no accretion either?

I know it was mentioned. but hypothetically, as I know we could not exist etc, with accretion and gravity, a planet could and could still be in orbit around a sun, which could not.

[Nakojo]

Sure, but what makes a molecule 'stick together', or an atom or how ever far down you want to go (really, same applies to gravitational or electromagnetic pull but I was trying not to over complicate matters)?

Movement, friction, mass, no matter how you look at it, once it's true, it is true.

And all the same

[Nakojo]

Allow me another angle, perhaps that will help.

Light. Colours.

General conception is that the colours we perceive are because of photons bouncing of the perceived object.

While this is not incorrect by itself, the truth of the matter is that objects have photon receptors. The colours we see are indeed a reflection of lack of absorption rather than some shield that thecphotons bounce off. All the same really but it's about understanding the how and why surely?

[moby]

Sure, but what makes a molecule 'stick together', or an atom or how ever far down you want to go (really, same applies to gravitational or electromagnetic pull but I was trying not to over complicate matters)?

Movement, friction, mass, no matter how you look at it, once it's true, it is true.

And all the same

So if you have a dip in an ice sheet, things dont stay there

[Nakojo]

I suppose that all depends on on how hard the object is relative to it's environment

[moby]

TBh I think I will pass on this. Mabe when I ave had a couple of jars I will mull it through

[Covalent]

Blinky and qczhao have both made good explanations; easy to understand and accurate.

[flyboy10]

Is a bowel motion possible without friction? I suppose gravity could take its course

[qczhao]

Hi Nakojo,

Let me try to expand on my points in response to yours. Hope it clears things up.

Sorry I read your initial post again and I don't see where you have addressed gravitational pull?

At any rate, I believe your other explanations are wrong as well. I'm addressing your points in line below.

In a vacuum it's slightly different, but it's still all about friction.

There can be no friction in a vacuum because the definition of a vacuum is a space in which there are no particles. Without particles to rub past each other, there can be no friction.

As there can be no movement without particles rubbing against each other - friction. Be they internal or environmental. In an absolute vacuum, there is no rocket. The absence of particles implies absence of mass, surely.

I think things are getting confused here. When I spoke about a vacuum, I was talking about considering the rocket to be operating in a vacuum because in deep space, the general condition is that it is in a vacuum (ignoring celestial bodies, asteroids, the rocket itself etc). That's not to say the rocket itself can't exist in a vacuum. Indeed, if that were the case, we wouldn't be here, because you can think of the Earth itself as being suspended in a vacuum.

I think the misunderstanding comes from the fact that you think there can be no movement without particles rubbing against each other. This is fundamentally incorrect. Forgetting even the action of electric, magnetic and gravitational fields, which we well know can influence motion without particles even coming into contact with one another, a force provided normal to a surface does not require friction to transmit. Let me expand in my next point.

The heated gas expands the exhaust, this tries to return to it's original shape -molecular bindings and cooling effect by it's surroundings-, thereby creating friction (between the gasses and the exhaust).
As the rocket meets no environmental friction, this is enough for thrust.
Where else are the expanding gasses and rocket going to go?

Friction is not the root cause for molecular bindings. The heated gas tends to expand because you are increasing its internal energy (by heating it), this means that each molecule of gas contains more kinetic energy which means it collides more frequently with the surrounding molecules, thus forcing the average distance between particles to increase to maintain equilibrium. If you contained the gas instead of allowing it to expand freely, you would get a proportional increase in pressure.

Anyway, in a rocket exhaust, the expanded gas is allowed to go only in one direction (out the exhaust of the rocket). Therefore Newton's 3rd Law tells us the reaction force must propel the rocket in the other direction.

I'm not disputing the 3rd law, I'm elaborating on it. Without the molecular binding (and friction) of the exhaust, the gasses would expand circularly. The exhaust 'pushing back', is what causes the propulsion, the directional force of the expanded gasses, so you like. Without that friction, there would be no acceleration (well, marginal, as it will be affected by the expanding gasses anyhow - again, molecular friction).

I think you're misunderstanding that friction has nothing to do with the molecular bindings in a solid structure (e.g.the combustion chamber of a rocket). Molecular bindings arise due to the electromagnetic force. This is not the same as friction. Friction also arises from the electromagnetic force but is not in itself the electromagnetic force. [edited to be more accurate as sub-atomic bonds are due to the strong nuclear force but inter-molecular bindings are due to electromagnetic force]

I don't disagree with the fact because the gas is re-directed due to the exhaust, then you have Newton's 3rd Law applying. I'm saying that this can happen even in a frictionless environment. The fact that particle collisions take place can happen without friction. e.g. if you dropped a ball coated with a frictionless material off a building and it landed on a frictionless surface it would still rebound according to conservation mechanics (energy/momentum). In fact, all physics questions at A-Level and even into University predicate the assumption that surfaces are frictionless and air resistance is ignored unless otherwise specified and the differences to real world results are in most cases negligible.

Not unlike a football, it's not the kick that makes the ball travel, the kick dents the ball.
The ball wanting to return to it's natural form (pressure) is the only reason it travels (it can't do so in the same spot, as the foot carries more kinetic energy -try kicking a cannon ball-).

The cannon ball travels far less than the football because of its mass. KE = 0.5 * mass * velocity^2. Therefore, if you have a cannon ball that weights 5kg versus a 0.125kg football (I looked up the weights), the cannonball is actually 40 times heavier, and so you can expect the velocity to be decreased by approx 6 times.

The ball itself travels because when you hit it with your foot you are transferring kinetic energy to the ball. Or, an equally valid way of looking at it would be that your foot exerts a force on the the ball, and a force results in an acceleration (Newton's 2nd Law). Whilst the ball is in contact with your foot, Newton's 3rd Law would be involved also, which says that the force exerted on your foot by the ball would the same as that exerted on the ball by your foot. You would find that your foot would decelerate during the impact phase with the ball.

Curiously (or perhaps not ), the loss in kinetic energy of your foot would be equal to the gain in kinetic energy of the ball.

Again, this does not contradict my statements. Without the object carrying more kinetic energy being displaced (much), the kinetic energy of the 'lesser' object will move. Action, reaction, right? But why? Friction. Without friction, there would be no transform of energy. The foot would simply travel through the ball.

So, just to illustrate my point again; collisions still take place without friction because friction is not the root force that holds molecules together. The collision case between my foot and the two different types of ball would still yield pretty much identical results regardless of whether friction was present or not. There are many ways to test my claim if you still doubt this.

Consider a sailing boat, the wind just 'bends' the sail.
The sail trying to return to it's original shape makes the boat move.

Unfortunately, I don't think this is the right way to think about this. The sail (and in this case I am thinking of the most basic, parachute type sails) provides a surface area across which a pressure differential can act. On the side of the wind, we have high pressure, on the opposite side of the sail, we have low pressure. Force = Pressure x Area, therefore we have a force. Once we get into more modern sail designs (like for example on a wind-surfing board), there are also other aerodynamic effects at play which enhance the pressure differential effect once the craft starts moving.

Same.
Only the frictional forces of the sail v those of the wind (the environmental gasses crashing into the sail) 'create' all this.
I'm talking pure basics here and have done nothing but apply these laws.

Unfortunately although you've applied the laws correctly (I don't disagree with that) the fundamental explanation for why this is happening is wrong.

Gravitational pull was addressed -not elaborated on- in my post's conclusion:

Back to OP: yes, motion is possible without friction, acceleration however is not (ignoring gravitatitional pull from other objects).

Sorry - I didn't see this

Odd how nobody disputes the F1 example, while the principle is exactly the same.
Or how people declare statements incorrect while they are in no way contrary to the arguments brought forward, supposedly discrediting said statements.

Quoting and applying laws is one thing, understanding them is quite something else, it appears.

I'll make it as simple as I can: movement (or rather acceleration) is the result of object-particles crashing into environmental-particles. Friction. All other arguments brought forward are merely an elaboration on this principle.
And, as I've tried to explain in both this post and the one previous, collision mechanics really for the most part have nothing to do with friction. Molecular bindings have nothing to do with friction. I think I agree with your applicable of Newton's Laws but I don't think your fundamental explanation for why Newton's 3rd Law occurs is correct in any way at all!

[Nakojo]

Sure, level A physics assume zero friction and a vacuum.
Only not to complicate matters, but the example you provided should be sufficient to clarify my thoughts.

If a ball bounces off a surface, we like to consider this collision without any 'loss' of energy.
However, is it not the simplest truth to acknowledge without resistance (friction) the ball would simply pass through the surface? Or like I stated earlier in the example of kicking a ball, without friction, the foot would pass through the ball. It's quite simple really.
Were this not the case, I'd imagine we'd be driving (amongst other things) 'perpertua mobile'.

As for quantum friction, well, leading physicist don't quite agree on this one; to categorically state that there is no such thing is somewhat presumptuous. Admittedly my assumption that there is, could equally be seen as presumptuous though

Assuming there is, all my statements stand without need of any amends.

If there isn't, I'll gladly eat humble pie and admit your superiority on the matter.

Edit: just occurred to me now, rehashing the 'sail argument'.
High pressure, low pressure etc, right?
Okay, we all know the temperature rises (linear) as the pressure increases.
But why, if not because of more molecules being packed into the same volume, thereby colliding with one another more frequently. These collisions cause molecular friction, with heat as its by-product.
Makes sense, right?
Why else (other than "it's the law") would the temperature increase?
Merely trying to explain in the simplest way I can why I support the notion of molecular and even quantum friction.

Please do continue challenging me, I find it most interesting

[qczhao]

Sure, level A physics assume zero friction and a vacuum.
Only not to complicate matters, but the example you provided should be sufficient.

If a ball bounces off a surface, we like to consider this collision without any 'loss' of energy.
However, is it not the simplest truth to acknowledge without resistance (friction) the ball would simply pass through the surface? Or like I stated earlier in the example of kicking a ball, without friction, the foot would pass through the ball. It's quite simple really.
Were this not the case, I'd imagine we'd be driving (amongst other things) 'perpertua mobile'.

As for quantum friction, well, leading physicist don't quite agree on this one, so to categorically state that there is no such thing is somewhat presumptuous. Admittedly my assumption that there is, could equally be seen as presumptuous though

Assuming there is, all my statements stand without need of any amends.

If there isn't, I'll gladly eat humble pie and admit your superiority on the matter

So the crux of the matter is this;

However, is it not the simplest truth to acknowledge without resistance (friction) the ball would simply pass through the surface?

The ball would not simply pass through the surface. The surface acts as a surface regardless of whether there is friction or not.

However, I have made the assumption in my theoretical world that if you remove friction you do not remove the electromagnetic force. So in my previous post I mentioned that sub-atomic forces are governed by the strong force, which is right. But inter-atomic forces are governed by the electromagnetic force - this I have clarified now (sorry it was not right before).

If you in your theoretical non-friction world have said that the electromagnetic force no longer exists because this is the root cause of friction, then it would be true that molecules would no longer have a mechanism with which to bind, and then in that case the ball would pass through the surface, because well, the ball and surface would not be able to exist as such because no atoms would be able to bind with one another (you'd just have one cloud of atoms passing through another cloud of atoms, neither of which would vaguely resemble a surface or a ball).

So, we could both be right and just debating based on different initial assumptions.

[Nakojo]

I never argued you were wrong, my friend

Btw, I did add some more thoughts on molecular friction in my last post, please -if so desired- honour me with your thoughts on the matter.

Fwiw, I enjoy 'challenging' laws.
Consider E=mCC.
Consider light.

You'd be stretched to find anyone stating photons carry zero energy.
You'd be equally challenged declaring they carry mass.

This does not mean E=mCC is false, it simply means it is true applyi gvcertain conditions and /or assumptions.

[qczhao]

Edit: just occurred to me now, rehashing the 'sail argument'.
High pressure, low pressure etc, right?
Okay, we all know the temperature rises (linear) as the pressure increases.
But why, if not because of more molecules being packed into the same volume, thereby colliding with one another more frequently. These collisions cause molecular friction, with heat as its by-product.
Makes sense, right?
Why else (other than "it's the law") would the temperature increase?
Merely trying to explain in the simplest way I can why I support the notion of molecular and even quantum friction.

This can get very complicated very quickly because you're asking about thermodynamics, and this is something I haven't studied for a while so I'm a bit rusty.

Anyway, as far as I understand, temperature is inherently a measure of how much potential energy a system has. Higher temperature systems have more energy (but we can't always extract this energy to do useful things).

Heat is not a by product of molecular collisions. Rather, in order to increase the number of molecules packed into the same volume (or, more easy to visualise, decrease the volume with the same number of molecules present), we have to put energy into the system. For example, imagine a sealed room with one wall that can be pushed inwards to compress the air in the room. In order to compress the air, we have to put energy into the system (in this example defined as the air in the room). Therefore the total energy of the system increases (because energy conservation says you can't destroy or create energy, only transfer it).

When the total energy of the system increases, it heats up, because temperature is the measure of the internal potential energy that a system has, and by transferring energy to it, you've increased this potential energy. The way this increased potential energy is expressed in this particular system is that each molecule has an increased kinetic energy and collisions become more violent.

The pressure increases because if each molecule is colliding more violently (and also there are more collisions as the volume is reduced), then it stands to reason that the average force exerted on the container walls would increase.

[Nakojo]

Edit: just occurred to me now, rehashing the 'sail argument'.
High pressure, low pressure etc, right?
Okay, we all know the temperature rises (linear) as the pressure increases.
But why, if not because of more molecules being packed into the same volume, thereby colliding with one another more frequently. These collisions cause molecular friction, with heat as its by-product.
Makes sense, right?
Why else (other than "it's the law") would the temperature increase?
Merely trying to explain in the simplest way I can why I support the notion of molecular and even quantum friction.

This can get very complicated very quickly because you're asking about thermodynamics, and this is something I haven't studied for a while so I'm a bit rusty.

Anyway, as far as I understand, temperature is inherently a measure of how much potential energy a system has. Higher temperature systems have more energy (but we can't always extract this energy to do useful things).

Heat is not a by product of molecular collisions. Rather, in order to increase the number of molecules packed into the same volume (or, more easy to visualise, decrease the volume with the same number of molecules present), we have to put energy into the system. For example, imagine a sealed room with one wall that can be pushed inwards to compress the air in the room. In order to compress the air, we have to put energy into the system (in this example defined as the air in the room). Therefore the total energy of the system increases (because energy conservation says you can't destroy or create energy, only transfer it).

When the total energy of the system increases, it heats up, because temperature is the measure of the internal potential energy that a system has, and by transferring energy to it, you've increased this potential energy. The way this increased potential energy is expressed in this particular system is that each molecule has an increased kinetic energy and collisions become more violent.

The pressure increases because if each molecule is colliding more violently (and also there are more collisions as the volume is reduced), then it stands to reason that the average force exerted on the container walls would increase.

I'm sorry, don't take this as being disrespectful or avoiding detailed debate, I do like simplifying matters though.

How does one 'add' energy?
Of course, when the total energy within said system increases, all you say is absolutely true.
The elaboration on 'more violent collisions' is as far as I can assess totally construent with my arguments.

I fail to see energy 'increase', other than back to square one, magnetic 'pull' or quantum friction.
In either case, it must 'draw' the additional energy from it's environment.

Dismissing increase of energy, I still need some convincing.

And indeed, we don't seem to be disagreeing much, rather than debating assumptions and their applications.

[qczhao]

Edit: just occurred to me now, rehashing the 'sail argument'.
High pressure, low pressure etc, right?
Okay, we all know the temperature rises (linear) as the pressure increases.
But why, if not because of more molecules being packed into the same volume, thereby colliding with one another more frequently. These collisions cause molecular friction, with heat as its by-product.
Makes sense, right?
Why else (other than "it's the law") would the temperature increase?
Merely trying to explain in the simplest way I can why I support the notion of molecular and even quantum friction.

This can get very complicated very quickly because you're asking about thermodynamics, and this is something I haven't studied for a while so I'm a bit rusty.

Anyway, as far as I understand, temperature is inherently a measure of how much potential energy a system has. Higher temperature systems have more energy (but we can't always extract this energy to do useful things).

Heat is not a by product of molecular collisions. Rather, in order to increase the number of molecules packed into the same volume (or, more easy to visualise, decrease the volume with the same number of molecules present), we have to put energy into the system. For example, imagine a sealed room with one wall that can be pushed inwards to compress the air in the room. In order to compress the air, we have to put energy into the system (in this example defined as the air in the room). Therefore the total energy of the system increases (because energy conservation says you can't destroy or create energy, only transfer it).

When the total energy of the system increases, it heats up, because temperature is the measure of the internal potential energy that a system has, and by transferring energy to it, you've increased this potential energy. The way this increased potential energy is expressed in this particular system is that each molecule has an increased kinetic energy and collisions become more violent.

The pressure increases because if each molecule is colliding more violently (and also there are more collisions as the volume is reduced), then it stands to reason that the average force exerted on the container walls would increase.

I'm sorry, don't take this as being disrespectful or avoiding detailed debate, I do like simplifying matters though.

How does one 'add' energy?
Of course, when the total energy within said system increases, all you say is absolutely true.
The elaboration on 'more violent collisions' is as far as I can assess totally construent with my arguments.

The method of adding energy isn't really important to be honest. But if we take for example our sealed room with a wall that can move inwards. You can push that wall inwards against the pressure the gas is exerting by using a man. Pushing that wall inwards requires a force which moves over a distance hence you have work done on the system. Therefore energy is transferred (from the man's body) to the system (compressed box of air).

I fail to see energy 'increase', other than back to square one, magnetic 'pull' or quantum friction.
In either case, it must 'draw' the additional energy from it's environment.

So the point here is that energy is not generated because molecules are "rubbing" past one another. Indeed, it's not possible to generate energy by doing this (rubbing your hands heats them up because you're converting the kinetic motion of your hands into heat energy, that's why you get tired eventually!). The energy that gets added to the system comes from outside the system itself (in this case the man pushing the wall inwards).

Dismissing increase of energy, I still need some convincing.

The key thing here is that temperature is defined (at least in some respects) as the average translational kinetic energy of the molecules (of gas). So, if you increase the kinetic energy of the gas by adding more energy (by pushing that wall inwards - remember, when you push that wall inwards you are doing work against the pressure that the gas is exerting - therefore you are increasing the energy of the gas), by definition the temperature will rise. You can't really dismiss the increase of energy in this case as it is interlinked.

And indeed, we don't seem to be disagreeing much, rather than debating assumptions and their applications.

[Nakojo]

Great read, thanks.

It's admittedly been close to 30 years since I studied physics (at Imperial College fwiw) and haven't worked in the field since.

My interest (and subsequent approach) is more philosophical these days, as you may have noticed, and I have found this discussion both educational and challenging.

Thank you for your patience.

I'll still beg to differ though, if only on the principle of added energy, as it again does not oppose my arguments.
Quite the contrary.

You rightly state that the method of adding energy (within a system) is irrelevant yet then continue to assume a state of increased energy without addressing the (source of) increase any further, whereas I imho did, or at least tried to sway the discussion that way.

[qczhao]

Great read, thanks.

It's admittedly been close to 30 years since I studied physics (at Imperial College fwiw) and haven't worked in the field since.

My interest (and subsequent approach) is more philosophical these days, as you may have noticed, and I have found this discussion both educational and challenging.

Thank you for your patience.

I'll still beg to differ though, if only on the principle of added energy, as it again does not oppose my arguments.
Quite the contrary.

You rightly state that the method of adding energy (within a system) is irrelevant yet then continue to assume a state of increased energy without addressing the (source of) increase any further, whereas I imho did, or at least tried to sway the discussion that way.

It has been interesting .

I'm not a physics grad, but a recent engineering grad but have always kept an interest in physics .

So on your final point, my question is if the method of adding energy to a system is irrelevant, then what does it matter about the source of the energy? However, the caveat to the previous statement is that we assume the method of adding energy to the system to be a valid one.

When you discuss an increase in energy due to molecular friction, from my understanding its an invalid way of adding energy to the system because friction merely transfers energy between two particles in a similar manner to collisions. So one particle might lose energy and another gain energy but the net change in energy of the two particle system is zero [therefore no change in temperature].

If you added a bunch more particles into the fray, you would increase the energy of the system because you added more particles, not because now there would more collisions and friction between the particles, because all that does is re-distribute the energy between all the involved particles to make their energy levels homogeneous.

Anyway, this kind of thinking is tricky because thermodynamics is really a macroscopic theory and we're looking at the microscopic explanations for it which I don't really think are well understood anyway (certainly not by me).

[Schumacher forever#1]

Well rocket motion doesn't depend on friction - does it?

Rockets get their motion before they leave a magnetic field; there is nothing in space to push the rocket.

[Irbis]

How does one 'add' energy?
Of course, when the total energy within said system increases, all you say is absolutely true.
The elaboration on 'more violent collisions' is as far as I can assess totally construent with my arguments.

I fail to see energy 'increase', other than back to square one, magnetic 'pull' or quantum friction.
In either case, it must 'draw' the additional energy from it's environment.

Dismissing increase of energy, I still need some convincing.

And indeed, we don't seem to be disagreeing much, rather than debating assumptions and their applications.

Consider particle accelerator like LHC. You have ray of particles in absolute vaccuum, nothing collides with anything else, yet we can increase/decrease energy in particle stream by slowing or speeding it up. No friction, no collisions, energy still exists.

Rockets get their motion before they leave a magnetic field; there is nothing in space to push the rocket.

Wrong. Ion engines work only in space, but they work without friction whatsoever. Momentum exists regardless of friction.

[stormwarning]

Friction = grip and will HINDER motion. Keep Einstein's "for each action there is an equal and opposite reaction" in mind:

Friction is NOT required for motion, as proven by rocket's in space where the Einstein thing above comes in quite nicely. But to bring that analogy down to earth, a car propelled by a rocket would follow the exact same law as the rocket does, but in the car's case, the 4 tyres in contact with the road create friction between the two surfaces, and the car itself in contact with the air causes more friction. These are not require for motion - they make it harder.

Now remove the rocket and put the power for the car though the wheels rather than a jet and the PROPULSION method has changed, but the same rules still apply (if they didn't, aero would mean nothing and big fat wideboy tyres wouldn't slow you down at all).

[Fangio52]

Hope I do not crash your party, but stormwarning and some others here are right. You don't always need friction nor electromagnetism for motions. What you always need to accelerate a body is Force. Even when there is no force actuating into a body, the body might be moving with a Uniform movement =with no acceleration= or just staying with no movement.
Some people get confused because when you move a car using its tires you need the friction between the tires and the tarmac to move the car but in the case you put a rocket engine or a turbine in the car with no connections to the wheels, the car will move independently from the friction with the tarmac.
Keep it simple and do not mix different things when analyzing things or you can just get a head ache.

[James14]

What was before the Big Bang? Take two aspirin before you read this..

Most of us think of space as having the three basic dimensions with time as the fourth just marching on. But before the big bang there was no space, no time, nothing, not even three dimensions. Nothing. Not even time.

Forgive my ignorance here because I am not that well educated.
But surely the material that combusted that caused the Big Bang needed space to exist and maybe time to be created beforehand?
Space must have existed before the Big Bang. Granted it must have been empty space. Otherwise the Big Bang would have been an implosion rather than an explosion.

Where are those aspirin? I need them now.

[flyboy10]

Well, depending on who you listen to and what your brain will allow you to believe, there is an argument that "empty space" and "nothing" are NOT the same thing.

Also, that there was nothing outside of the matter that created the big bang - so NOT empty space but actually just NOTHING.

Finally, at the edge of what we call space now, everything just ends and beyond the last bit of space there is nothing, not more empty space.

As humans we suffer from thinking about things in terms of our own internal view of how we expect things to be so we ask, "What was there before the big bang?" and "What is outside of space?".

[Alienturnedhuman]

Is motion possible without friction? Yes. You can do it without leaving your chair. Take a coin out of your wallet/purse. Hold it one metre off of the ground. Let go. It will move. Friction will play no part in its acceleration. The only friction in the system - the air resistance - will serve to slow it down.

If you want a more useful example, and one with no friction at all, then a maglev train in a vacuum tube.

Or an electron orbiting a proton.

Most of the arguments on here claiming friction is always needed are actually arguments of semantics rather than science.

[Alaaddin]

Of course, motion is possible without friction like we can say this claim without using any letters and without any sound. It is confusing and it may not be seen as scientific as well. And what is science first of all? There is a bunch of people who try to explain everything WITHIN science. Yet, they can only have guesses (some of them are very close to truth though) for the first minutes of Universe, Dark Matter, inner characteristics of event horizon, let alone finding some information about spirits and afterlife.

It is all about having rules throughout the Universe that can also be changed with permission*. So once you got the permission (not many got that) you can learn and do the permitted actions that supposedly were impossible before.



*It seems laughable but true nonetheless.

[Blinky McSquinty]

What was before the Big Bang? Take two aspirin before you read this..

Most of us think of space as having the three basic dimensions with time as the fourth just marching on. But before the big bang there was no space, no time, nothing, not even three dimensions. Nothing. Not even time.

Forgive my ignorance here because I am not that well educated.
But surely the material that combusted that caused the Big Bang needed space to exist and maybe time to be created beforehand?
Space must have existed before the Big Bang. Granted it must have been empty space. Otherwise the Big Bang would have been an implosion rather than an explosion.

Where are those aspirin? I need them now.

It is really more than difficult to get our heads around the concept of "nothing". The classic concept of Newtonian space is three dimensions, and time. That is the concept most of us can get our heads around and comprehend. Einstein's concept replaced Newton's where space, speed, and time interacted and were warped by gravity (the space time continium). Even though there may not be a single electron within a billion light years from that place, it exists and has all four dimensions. Therefore it exists, and is "something". It has four dimensions, and light, radiation, and Captain Kirk can travel through it, even though at the moment it is "empty".

But there is a concept in physics (who knows, it's all theory) that one scenario before the big bang that it was "nothing". It did not enjoy three dimensions, or time. Light, radiation and Captain Kirk could not travel through it, time did not exist, the three dimensions did not exist, it did not exist. It was nothing.

This is a concept that cannot be digested in one bite. If you shake your head and feel confused, because you believe that the three classic dimensions and time are inviolate, and just have to exist, it's OK. They must exist, right? Everything I see, know, and have learned tell me that there has to be three dimensions and time. That's what I thought too, but it took a very long time for this radical, scary, and weird concept to sink in.

The concept that before the big bang, and maybe outside our expanding universe, there is "nothing".

[bbobeckyj]

What was before the Big Bang? Take two aspirin before you read this..

Most of us think of space as having the three basic dimensions with time as the fourth just marching on. But before the big bang there was no space, no time, nothing, not even three dimensions. Nothing. Not even time.

Forgive my ignorance here because I am not that well educated.
But surely the material that combusted that caused the Big Bang needed space to exist and maybe time to be created beforehand?
Space must have existed before the Big Bang. Granted it must have been empty space. Otherwise the Big Bang would have been an implosion rather than an explosion.

Where are those aspirin? I need them now.

The name "The Big Bang" is a misnomer.
Please forgive me if I'm unintentionally being patronising, but there was no combustion (burning) or explosion involved in the big bang. Burning is a chemical reaction between a fuel and oxygen, but there was no oxygen immediately after the big bang, only hydrogen and helium, (burnt hydrogen is water), all of the other successive elements were created by fusion in stars.
The big bang theory doesn't explain what there was or wasn't prior to the event. In extreme layperson speak, all matter spontaneously popped into existence in a singularity, an infinitely small thing of infinite mass. Then Inflation followed, a period of sudden expansion, because no thing can occupy the same space as another thing. All particles repulsed each other until they were no longer occupying the same space, (visualize a sponge squeezed very small, and released, a sudden expansion followed by slower continued expansion), then once that was done the universe continued expanding at a slower rate.
(Cue the really clever people picking holes and explaining it a lot better than I.)

[Alex53]

Most of us think of space as having the three basic dimensions with time as the fourth just marching on. But before the big bang there was no space, no time, nothing, not even three dimensions. Nothing. Not even time.

How can there be a 'before' the big bang, if there was no time?

[Alex53]

What was before the Big Bang? Take two aspirin before you read this..

Most of us think of space as having the three basic dimensions with time as the fourth just marching on. But before the big bang there was no space, no time, nothing, not even three dimensions. Nothing. Not even time.

Forgive my ignorance here because I am not that well educated.
But surely the material that combusted that caused the Big Bang needed space to exist and maybe time to be created beforehand?
Space must have existed before the Big Bang. Granted it must have been empty space. Otherwise the Big Bang would have been an implosion rather than an explosion.

Where are those aspirin? I need them now.

The name "The Big Bang" is a misnomer.
Please forgive me if I'm unintentionally being patronising, but there was no combustion (burning) or explosion involved in the big bang. Burning is a chemical reaction between a fuel and oxygen, but there was no oxygen immediately after the big bang, only hydrogen and helium, (burnt hydrogen is water), all of the other successive elements were created by fusion in stars.
The big bang theory doesn't explain what there was or wasn't prior to the event. In extreme layperson speak, all matter spontaneously popped into existence in a singularity, an infinitely small thing of infinite mass. Then Inflation followed, a period of sudden expansion, because no thing can occupy the same space as another thing. All particles repulsed each other until they were no longer occupying the same space, (visualize a sponge squeezed very small, and released, a sudden expansion followed by slower continued expansion), then once that was done the universe continued expanding at a slower rate.
(Cue the really clever people picking holes and explaining it a lot better than I.)

Is there a chance that time does pre-date our universse and the big bang only describes the beginning of this particular universe we are in now? i.e. universes are born out of some kind of 'dead universe' black hole?

[bbobeckyj]

Is there a chance that time does pre-date our universse and the big bang only describes the beginning of this particular universe we are in now? i.e. universes are born out of some kind of 'dead universe' black hole?

I tend to think of time as an effect of entropy or increase in disorder. If there was nothing to become more disordered, there couldn't be a change in time.
My hypothetical thought experiment/puzzle that leads me to take this view is this: If all movement, chemical reactions, four fundamental forces (and anything I don't know of or forgot) were temporarily stopped, would time also be stopped?
An observer within the system would be affected by the stoppage and thus would be incapable of being aware of it.
And if there was an outside of the universe, an observer would see it stop, but the observers inside still wouldn't notice it, so even though the universe is a hypothetical closed system within another system, time would still be considered to be unchanged for the duration of the pause. Adding the 'outer' universe just leads to an infinite regress, so its existence seems irrelevant and unlikely.

This is also the reason I have for rationalising the impossibility of time travel back in time. The disorder of the entire universe would need reversing, while at the same time the time traveller and the mechanism of doing so would need to be removed from the system, and then re-inserted earlier (or later depending upon which observer's point of view), which also implies that both couldn't be part of the system. The energy required to do this intuitively seems to be more than is contained within the system. I wonder if a change to only a small local area could be attempted, but I'm rambling far from the topic, and likely talking nonsense

[Blinky McSquinty]

That's not completely nonsensical, bbobeckyj, just asking good questions. But everything has to follow the laws of physics, the problem is that we don't know all of them, and may not be correct on some. A good part of theoretical physics is just that, it is just theory. Newton's theories were valid until they were replaced by Einstein's theories. And who knows, one day his theories may be proven incorrect or incomplete.

But what you are describing sounds like what happens in a black hole. If someone feel into it and actually remained in one piece and did not fry from the radiation, to that person time continues as usual. To the outside observer watching from just beyond the black hole's event horizon, the person falling into the black hole appears to slow down, slow down, and then cease all activity, time appears to have stopped. But it's all a complex relationship between gravity, time, and space.

Here's another weird thought and source of headache. Time is not the same for everyone, it runs differently based on their velocity. An airline pilot who flies at 600 MPH for a good part of his life actually lives longer than if he did not. The time difference is not much, but it's still there.

We hold to the concept that time marches on at a constant rate, and that it is constant throughout the entire universe. But it's not.

[chaz986]

A frictionless engine would be very good ,a lot of energy is used up driving parts even though an engine runs on oil an oil pressure there is still a fair amount of drag caused by the oil even though many parts flot apon an oil film