Question

question about third law of newton's physics: it seems others may get it wrong, but is it real that any force should account for counter-step?

Answer 1

for every action there ll be equal reaction... thats true in every aspect.. jst think u ll get it.. or punch a wall behind you.. u ll feel the pain.. then u ll be knowing about reactions ;)

Answer 2

Jumping is another example. Your applying force on the floor and it "reacts" by applying the same force on you and since you're not massive enough to resist it, you "fly" until gravity wins again and brings you back down. The ground doesn't move when you apply force on it because it's too massive kind of like how the Earth doesn't fall out of orbit because you stomp the floor.

Answer 3

there exist always a pair of forces but the problem is this that equal forces are exerted by 2 different bodies on each other so people take it that it must cancel out or some take themselves as a reference so it is just a game of frame of reference:)

Answer 4

there arent any single forces in nature forces exist in pairs, you walk forward by pushing backwards on thearth similar to jumping up by pushiong downwards on the earth; very related to conservation of momentum as in an explosion?

Answer 5

force is an interaction between objec ts

Answer 6

clearly, switching states or levels of acquiring or losing kinetic potential. it depends on mass, gravity, how matter absorbs energy when losing forcing momentum thus reducing speed.

but at same time, being "at rest" already assumes certain level of kinetic potential only due to mass, intertia.

interesting - law of conservation of energy here would clearly indicate losing kinetic energy as anything requiring compensation of speed for staying at same unaccelerated constant motion.

Answer 7

still unclear what is that other equal force

Answer 8

if there is an object which pushes other then the other one would pushes the first one with the same force.let us make it more clear with practical example what happens to your hand if u punch (a) a person then (b) a wall??????
answer me then i will procede...........

Answer 9

wrong

Answer 10

what wrong?

Answer 11

there's no other force
just the initial one

Answer 12

No, you are wrong, there are 2 forces, always.

Answer 13

it's bad example

Answer 14

it's some complex motion, I was referring to force that starts affecting object, any force, no matter how it appeared

Answer 15

So what is your question?

Answer 16

how this equation works out: F=ma ?

Answer 17

"for any action there will be equal reaction" - explain more. what is action, and per se, reaction? you mess terms altogether, this is not professional.

Answer 18

"No, you are wrong, there are 2 forces, always." explain that in more detail

Answer 19

how does that refer to relativity?

Answer 20

you should ban for such answers

Answer 21

hey do your homework yourself!!! you will not get properly educated if others will do stuff for you.

Answer 22

that's thing: this is not homework, I'm getting advise, not asking for doing job for me. Comprende?

Answer 23

Sure... Likely story.

Also, getting advise will not get you 'properly educated.'

What's the difference, really?

Answer 24

Well, I'm not genius, you know.. I have *some* talent, but I'm stupid no less than those who get well paid

Answer 25

And getting advises by the way, is more about sharing *knowledge*, not *copy-and-pasting*, which clearly are not the same.

Answer 26

I failed to notice the difference from your statement. Your question can be copied, and you can copy replies and use them as answer. It's basically the same thing.

Beside why did you give me medal?

Answer 27

Moderator told me "they liked kudos" ;)

Answer 28

"sharing knowledge" is bilateral. meaning that I AM one who possessed knowledge HAVE TO MAKE SURE you're getting it properly. What is different between seeing and knowing, anyway?

Answer 29

Ok, concerning topic -

ma=F (it seems better that way) is something that (at this point, seemingly) works out only for explaining MOTION OF SOLID BODY objects.

Answer 30

"force is an interaction between objec ts"

what is FORCE, once again? Define that by avoiding Newton and mechanics of solid body objects.

Answer 31

where there is constant motion that law is applicable once acceleration is involved the system will be unbalence therefore the third law will be left out that that make sense peeps?

Answer 32

what comes first: force or energy?

Answer 33

if energy does not disappear what is discriminant of dE/dT=(constant)m/(constant)x-y-z coordinate

(approach that by applying knowledge of closed-balance systems)

simply, if anything requiring compensation of energy for being in same state, stays at rest, what is that anything that forced it losing potential (besides that initial condition)?

as well, if matter does not disappear or move, what defines energy of that equilibrium?

Answer 34

force is physical application of changing energy potential.
what is energy, then?

something that precedes matter in E=mc type of stability

approach that through wave-particle dualism

Answer 35

"third law will be left out" - not sure I understand that.

again, F=ma only seems abusing once changing energy potential requires physical intervention.

ma=F seems valid, but only due to paradigm of acquiring kinetic potential. So, growth of speed requires force, losing of speed assumes compensation of energy, which is actually dependant on way of observing that change.

Answer 36

@gerryliyana help him i personally think that you can make him understand:)

Answer 37

@Aperogalics - that is thing, there's nothing to understand, it is not there, not in my reality.

Answer 38

force creates energy differential, that what causes motion or reconfiguration of matter. you cannot compare them, they belong to different reference frames

Answer 39

All right I jumped some posts and I will start from the begining.
Force is exacly what it seems, you acelerate your car, you feel a force thats what it is.
Newton defines it as dp/dt, where p is the momentum. What does that tell us? It tells us that something we call force makes the momentum change. Momentum can be seen as quantity of movement, so forces increase or decrease the quantity of movement.
Now lets look at energy, it is something we atribute to the state of the system and what it can do. And we know it is something that remains the same always, but what is it?
It is not something we just define, but we understand how it relates to the other aspects of mechanics. So, gravity for example. When we raise something, we are making a force on it, to beat gravity and raise an object, we know that if we release this object it will gain speed because of gravity, so where does energy comes here? There is clearly something that changes between one state and the other, on the first there is a ball, that we made a force to raise, and on the next anoteher force made it fall, so that force that made the ball fall was already there and since the ball was free to move, it moved, now what does this "free to move" means, it means that that state needed to change because it could. We say that it has a potential to move, a potential energy, and what happens with this potential? It becomes movement, kinectic energy, now we see what we mean when we say that a system goes to the state where it has the minimum potential energy, it means it can move and it will. So potential energy is closely related to force, and actually one generates another simultaneously. The greater the potential energy, the greater the force is. But if that was all, we couldn't say it conserves, but lets say we are already moving, and we climb a hill with that movement, we gained potential energy because we went from a stable state to a state that requires us to go back if we are able, so movement by itself can create potential energy, so we can say that movement already has a certain amount of energy in it because it can put us on a state where we lost the movement we had, but gained potential to move, in other words, potential to move and movement are two aspects of the same thing.
Now lets take a look at the relationship between energy and force. We say that a force generates a potential energy, but if we are unable to move, we won't. So when does a force changes the potential energy of the system? When it moves something. We call that work, when a force does a work it changes the potential and kinectic energy of the system and this work must involve movement and it is directly proportional to it.
Now we are ready to look at the third law.
As I said before, force changes the quantity of movement. Now, whats the diference between quantity of movement and energy? Lets look at an example, we have a ball alone in space, and instantly a force begins to act on it, that is purely hypothetical for it cannot happen, but thats ok, the ball now has potential energy, and it will move, but this energy will keep constant after that. But where does that energy came from? Probably from the work we made to get the ball to the area of influence of the force or the other way around. Now look at the momentum, or quantity of movement, the ball will start to move, and it will gain quantity of movement, but the energy didn't change. The hole system is gaining quantity of movement. Now imagine the ball alone again, and imagine it is made of particles, those particles interact with each other but as we knew before the quantity of movement of the hole system does not change. If they are interacting it means they are making forces on each other, but doesn't forces change the quantity of movement of the system? Yes they do, but we know that the quantity of movement does not change. If we know that, it means that in the hole system, the forces must be zero, but how can this be if we know that there are forces inside the system? It can only happen if the forces inside the system cancel each other. Now lets think that system is made of only two particles. In the hole the system is still, and we know that the force acting on the hole needs to be zero too, but there is gravitational forces acting, so the only way that the energy is zero, is if at the same time that one particle atracts the other, the other atracts the first in a way that the hole quantity of movement remains constant, that means that in a closed system, a force needs to have another to balance it otherwise the system as a hole would move and that is not possible since there are no external forces.
That is the theory, now lets do some examples:
If you climb on a ball, and walk, the ball will gl backwards and you will go forward, that does not seem to happen when we walk because the earth moves too little because the quantity of movement is also proportional to the mass (two trucks have more movement than one) so we gain quantity of movement, but we are not a closed system, the closed system includes the earth, and tha earth gains quantity of movement in the other direction therefore making the system have the same quantity of movement.
This is long, but I hope it helped., I tried to be as thorough as possible.

Answer 40

appreciate such level of detalization; also, i make these notes to above commentary:

1. too many assumptions
2. described approach to systematic measurement goes out of scope
3. particles are not solid-body objects, as well amount of space should also be described as part of system
4. movement is not something that belongs to force-energy transformation mechanism, matter absorbs energy at certain levels without viable method of measuring change of coordinate of mentioned equilibrium
5. force and energy clearly are not physical and exist only due to reconfiguration of matter, however it accumulates around pattern of stability is causing stable mass and inertia - so, matter and space seem to precede energy and involvement of force in our understanding of closed-balance systems; moreover, it comes to defining reconfiguration of space, however it exists and whatever makes it change approach to measuring its quality

to me it means that singular model of space at certain point becomes lose, which is loss of matter, non-zero probablity of acquiring or losing energy potential, anything that results in unexpectedly ended experiment is impossible to describe and in best situation is recorded as something that failed to prove suggested formula, in worse case scenario just left unexplained or sabotaged.

Answer 41

What you're trying to say is that F=ma is just damn strange ?
You might want to see this before you start linking energy and F=ma
http://www.eftaylor.com/pub/newton_mechanics.html
the equation is based on that the energy(wherever it came from) will "produce" a "force" (which of course is mediated by other particles) that will procude an acceleration.
Force doesn't necessarily change "energy potential". Push against a wall and tell me you're trying to change the energy of the wall.
Force is something that can change the speed or direction of something else. Whether it does work depends on how its applied.

Answer 42

"Whether it does work depends on how its applied" this approach seems lousy, I can explain that situation "Push against a wall and tell me you're trying to change the energy of the wall" with better detalization

Answer 43

There would be internal friction.
A force doesn't really need energy to produce. Take gravity as an example. However,that force can change your acceleration status,by F=ma. Acceleration does not produce a force. If it did, we could have produces perpetual motion machines. Bu then again, how do we accelerate?

Answer 44

1. The assumptions were made in order to show specific aspects of the concept being discussed, and most were removed when going to more general points.
2.I don't know what you mean here, but I know what out of scope means, so I might agree with you that there can be some things that are out of scope but I though they would be helpfull in understanding the idea I was trying to transmit.
3. You are correct here, but those notions can be easily transfered to solid bodies, since they are a closed system of many ordered particles. The last part I'm not sure I understood what you meant.
4. What I meant when I said "movement" was kinectic energy, but since I was trying to get to this concept I couldn't use it. So, the kinectic energy becomes potential when a force is being applied to make that particle stop moving. The example I used was that a ball climbing a hill loses kinectic energy and gets potential energy in return. That is made by climbing the hill, wich is an action that the force of gravity makes stop, therefore making a work that is reflected as a change in kinectic energy to potential energy. Thats why work has unit of energy. If when you talked about absorbtion of energy of a solid, you meant something like light, all of these notions apply, but light has some diferent properties that makes this things harder to analyze.
5. I'm also not sure of what you meant here, but force is definetly physical, it is what reordenates the systems, and this definition can go on both ways so reconfiguration is what forces do, it is not a preceeding concept but a simultaneous one, and energy is what limit the possible reconfigurations so it is all one big picture where we can't ask who came first.

The last paragraph I do not understand where you took those conclusions from, but the third law (wich is the subject of this hole discussion) is a way of preserving the simetry of time, that says that energy must be conserved. If there were no 3rd law, momentum would not be conserved in a closed system and energy also would not be conserved.
I'll go now, but tomorrow I'll see any answers

Answer 45

when you're mentioning "law of conservation of energy", remember it does not always work, try finding out when it doesn't.

Answer 46

I couldn't think of any situation, some might seem wrong but when I look at a bigger picture there is always conservation, what was the situation you were thinking of?

Answer 47

"There would be internal friction. " this seems over-reactive

Answer 48

"I couldn't think of any situation, some might seem wrong but when I look at a bigger picture there is always conservation, what was the situation you were thinking of?"

find it

Answer 49

" http://www.eftaylor.com/pub/newton_mechanics.html "

this has to be banned for using inappropriate language of describing mentioned physical phenomena

Answer 50

All kinds of friction increase temperature, wich is the kinectic energy of the particles that make the solid, so the energy is transfered not lost. The situations we usually think are situations like friction, chemical energy, like on a bomb. The bomb explodes and it seem that energy was created, but it was already there.

Answer 51

"wich is the kinectic energy of the particles that make the solid" this is freevolous statement, i don't like it

Answer 52

newton's vision of mechanics does not apply to atom-level or description of behavior of particles; it may relate to thermodynamics, however i would rather conside Kelvin instead of Newton here.

Answer 53

* Calvin

Answer 54

I'm sorr, but I do not understand if 'inappropriate language' refers to the standard of english used in the material or that it uses calculus to derive it?
It may seem counter intuitive that a force produces an acceleration instead of the other way around, and that force is something that changes an object's momentum wrt time, but something that is accelerating does not create a force until it collides with something else, and that something has its momentum changed wrt time. However, that is the case of conservation of momentum.
Force can be something that is not caused by accelerating mass. Take gravity for example.

Answer 55

well, depending on what you mean by "particles", again, it would rather be appropriate for thermodynamics

Answer 56

"but I do not understand if 'inappropriate language' refers to the standard of english used in the material or that it uses calculus to derive it?"

no, but rather approach to explaining physical phenomenon

Answer 57

"It may seem counter intuitive that a force produces an acceleration instead of the other way around"

force can only produce that due to described inertia, no more or less than object's mass.

Answer 58

"However, that is the case of conservation of momentum" can you refer to any literature describing that?

Answer 59

"Force can be something that is not caused by accelerating mass. Take gravity for example."

how does that relate to newton?

Answer 60

That statement was not frivolous, I meant it, the random movement and vibration of the particles that belong to a solid is what we feel as temperature, so friction does conserve energy. In this case newtonian mechanics still apply, because the particles that make a solid move acording to newtonian mechanics, and vibrate as such, some phenomena might not be described by newtonian mechanics but this is. Even the vibration of the particles (by particles I mean combination of atoms) is well described as if they were connected by a string in newtonian mechanics.
What he said about inapropriate language doesn't matter, since it is all names, not something related to physics.
Secondly, you all seem to be confusing what newtons second law is. It says that F=ma, but what force is that? Its the total force acting on a body, so gravity does cause an aceleration but it is perfectly balanced with another force, called normal force, that is the force that the floor makes on us to stop us from falling into it. That is again newton's third law. Now imagine this law is wrong, how would you explain that we don't fall into the earth?

Answer 61

Ok, before you answer, what is exactly you think is wrong, or inapropriate on newton's laws and mechanics? Please keep the english simple if possible, and be clear because I think we are running is circles on this discussion now.

Answer 62

1. newton provided description of laws; actual "laws" exist in reality beside newton. i hope this is clear.
2. newton's vision of "force" and thus "energy" seems improper at certain points, especially when it comes to description of different frames of reference and closed-balance systems

big question is how "force" becomes physical
as well, how energy exist in physical world, rules of its propagation and transformation

It seems I become hater of Newton's vision of world, I will try as much as I can to define same physical phenomena avoiding Newton and his laws.

Answer 63

You are correct that newton's laws do not apply to accelerated frames of reference without the need to consider forces that are not there (inertial forces), but even this approach describes the world perfectly (I'm not talking about relativistic situations or subatomic physics).
Can you give an example of a closed-balance system, I don't understand what you mean by that.
Force does not becomes physical, it was defined to describe something that we feel and that we see acting, so it is based on the physical world, already being a part of it even without newton. As to energy, it is something that we don't actually "see", like force, but something that we noticed its conserved on the world. This comes directly from the simetry of time, two instants must be equivalent always if the other aspects of the system remain the same. From that we see that the total energy cannot change with time, because then two arbitrary instants would not be equivalent anymore, and that is not something that its already on the world but a concept that was created to describe the world.

Answer 64

right now I'll hold to this formula:

dE/dT=(constant)m/(constant)L

where

dE/dT is difference of energy happened over difference in time
m is mass
L is location

Answer 65

consider energy as temperature at this point

Answer 66

Yes, mathematics are very reliable and solid tools to approach and explain physical phenomenon. Newton was the first to use calculus to describe physics though, so he's quite famous.

I'm sorry, but I don't quite follow the 'inertia' line. Inertia is a virtual property at best, its a easy-to-grasp concept for students that has just entered Newtonian mechanics.Inertia is "resistance to change in motion", didn't you realise you can't count it and you only know that it is directly proportional to mass? It's virtual, that means it's for easy understanding of the relation between Force and Momentum.

I'm sorry, but:
1) Force is something that changes an object's momentum wrt time. Producing an acceleration is a consequence of it. That is what Newton first derived. Please understand this.

2) Any reliable college textbook on physics or Wikipedia will show you that conservation of momentum is a consequence of Newton's laws.
Here's a good place to start, if you don't mind the maths,
http://en.wikipedia.org/wiki/Newton's_laws_of_motion
http://en.wikipedia.org/wiki/Conservation_of_linear_momentum
There's also Serways Physics for Scientists and Engineers, a textbook.

3)Newton did not ascribe energy to force. What he did was to give mathematical laws to describe motion, even though it's only sufficient at speeds very low compared to light speed. You can say he almost divorced force from energy, the only link between them left is momentum.

Essentially F=ma is a dumbed-down version of F=dP/dt if the students of the level are not familiar with vector differentials. My school taught this before high school level, before we learnt differentiation.

Answer 67

But then again, by looking at your answer to Ivan, I suggest this:
1)Consolidate your understanding of Newtonian mechanics. What's its about and how does it work. Refer to textbooks and try their questions that are related to the concepts. Understand why it doesn't work and how RELATIVITY comes to play.

2) I'll not comment on your equation. You'll understand how it's, um, peculiar, after you get to know Newton and Einstein's work.

3)Now, you can go and get the answers you're looking. It's in quantum mechanics. It's even more mind boggling and counter intuitive than Newtonian mechanics and I strongly suggest that a firm understanding of general physics, especially, Newtonian mechanics, relativity, and electromagnetism before you start or you might find yourself going down a stray path that might be wrong. I've been there and it's quite difficult to turn back.
You will find that force...um, doesn't exist and there exists simply "transfer" of momentum between mediatory particles. For example, the electromagnetic force is mediated by photons by using them to "transfer" momentum between electrons.