force = mass x acceleration

[CPL.Luke]

spunnery you essentially just stated newton's laws except with the word momentum replaced by force, whilt also keeping the word force in the original definition of force.

[spunnery]

spunnery, sorry if this seems like piling on, but the exact usage of terms that are defined unambigously demand preciseness. It is not like the regular English language (or other spoken word), where there are subtleties, and slight changes of meaning, and words that mean one thing in one context and mean another thing in another context.

 

Physics and mathematics demand very precise and correct use of the terms. You want to talk with other physicists and people who understand this material, right? It is just like learning a language, but a language with very little use for ambiguity. A force is defined exactly how it is, you cannot just change what it means. So, defining F1 as you have, and calling it a force is, quite simply, meaningless. [math]Force \ne mv[/math].

 

So, in order to convey your ideas with other people who are knowledgeable, you need to learn the correct terminology. Yes, force is a vector quantity, but so is momentum. Just because two quantities are both vector quantities does not imply anything special, like equality. Why not use the position vector then? By that same logic, position and force should be equal. As should acceleration, and rotation, and the derivative of acceleration, etc.

 

To respond to your "logic behind my explanation," quite simply in light of what I and the others have said above, there is no logic at all. What you have written is pretty close to having zero meaning. Since the very first equation your attempt to redefine force, is flawed, everything you dervied from that equation is wrong. It's like building a home on a sinkhole. It doesn't matter how well-built the first floor is, the ground the house is sitting on is sinking and everything will fall down.

 

p.s. As an aside, even mathematics and physcs aren't immune from some language-ambiguity creeping in, there are two different meanings of the word homogeneous in mathematics, for example. I am sure there are others. That said, both definitions of homogeneous are very exactly defined, and it is unlikely to confuse one with the other. Unlike your attempt to redefine force and then use the correct formula later, where confusion is rampant.

I appologise for my bad habits(to explain something not precisely)

 

So i will start from zero again.

The term force and it's defenition(formula also)s has to be redifined.

The term momentum and its defenition(formula also) has to be redifined.

 

A moving body have a force acting on it and it is equal to mass of body multiplied by velocity of the body.( earlier momentum)

 

To change the magnitude or direction of this force in a given time't',you have to apply an say an EXTRA force /time to achieve the required result.

 

Wait ! I will explain it more precisely.

 

Consider a body of mass 'M' at a certain height above earth(not too far).

The body was dropped from there.The gravity as per our new defenition will is acting on the body as a downward pulling force = M x 9.8 kg.m/sec. (Mass is multiplied because gravity is irrespective of mass-Also see denominator is only second instead of second square).

 

So,because of the gravity pull (ignore other forces) after 1 second the body will be at 9.8 meter below the drop point,and as per our new defenition of force, a force of M x 9.8 meter /sec is acting on it(because of displacement).

Now at that moment ,gravity is pulling the body again at a force 9.8meter/sec.

So the total force vector will be M x 2 x 9.8 meter/sec.Now the total velocity at the end of 2 second will be 19.6meter/sec.This means the body is accelerating and this is because of the addition of existing force in the first second and the pull exerted by gravity in the second second.

 

I hope, now my perspective is clear(correct or not is the second question)?

[swansont]

So i will start from zero again.

The term force and it's defenition(formula also)s has to be redifined.

The term momentum and its defenition(formula also) has to be redifined.

 

 

No, they don't. You need to use the terms as they have been defined for hundreds of years.

[insane_alien]

why would you need to redefine the basic definitions in kinematics to describe why a force perpendicular to motion will produce no change in speed.

 

it will change its velocity as that is a vector. but it only changes direction, not magnitude(the magnitude is speed). this is not hard to understand. infact, i taught it to some kids in 3rd year (13year olds) physics when i helped out in some physics classes. they actually understood it, even though before that class they had never even heard of a vector.

 

it takes force to change direction and since momentum is m*v this is also a vector quantity so it takes force to change the direction of momentum.

 

m is a scalar quantity so its not the important part. as long as the force is perpendiculat to motion there will be no change in speed. even though there is an acceleration.

[spunnery]

why would you need to redefine the basic definitions in kinematics to describe why a force perpendicular to motion will produce no change in speed.

 

it will change its velocity as that is a vector. but it only changes direction, not magnitude(the magnitude is speed). this is not hard to understand. infact, i taught it to some kids in 3rd year (13year olds) physics when i helped out in some physics classes. they actually understood it, even though before that class they had never even heard of a vector.

 

it takes force to change direction and since momentum is m*v this is also a vector quantity so it takes force to change the direction of momentum.

 

m is a scalar quantity so its not the important part. as long as the force is perpendiculat to motion there will be no change in speed. even though there is an acceleration.

Sorry,the problem for me to understand this is because I am not a thirteen year old kid. Could you please explain me how in kinematics,the speed of body will not change if the force is acting perpendicular to the motion.

Imagine Somebody is riding a bike at a speed of 10 km /sec. A huge truck at a speed of 100 km/sec come perpendicular to the bike and hit it.shall i beleive that only the direction of the bike will be changed? not the magnitude?

what if the bike hit perpendicular to the truck?

[insane_alien]

thats not really a good case, see, the force will only be perpendicular for a tiny tiny fraction of a second and then its parallel.

 

a better example is a ball on a string and spinning it round, you can spin it at a constant speed but you still need to provide a force to keep it going in a circle. if you release this force(let go of the string) it flies away. this is an example of providing a force without a resulting change in speed. the velocity however changes direction all the time which is what the force is causing. this is an acceleration.

[spunnery]

thats not really a good case, see, the force will only be perpendicular for a tiny tiny fraction of a second and then its parallel.

 

a better example is a ball on a string and spinning it round, you can spin it at a constant speed but you still need to provide a force to keep it going in a circle. if you release this force(let go of the string) it flies away. this is an example of providing a force without a resulting change in speed. the velocity however changes direction all the time which is what the force is causing. this is an acceleration.

what is the meaning of not really good case?.you are not sure? And please I am not looking for an example for change in direction due to the action of two forces.

[spunnery]

It's inside the moving body, spunnery. If you let the handbrake off a car and push it, you're exerting force on it to get it going. If you push it for say five seconds you're giving it some amount of "momentum". Then you stop pushing, and the force has gone into the car. There's no force acting on it any more, but it keeps on going because it's got that momentum. If you run round and get in front of it, the force it hits you with depends on how fast you stop it. Ummm. Don't try this at home.

 

The easiest way to think about what's going on here is to imagine that every atom of the car is tracing a circular path. When you pushed the car you bent these little circles into spirals, and every atom of the car moves forward, and keeps on moving forward. You have to push the spirals back into circles to stop the car moving.

 

Like the other guys said, do pay attention to the terminology.

The force has gone into the car? Admit ,force is still acting on the car and keeps on mooving the car untill another force acts on it.

[insane_alien]

what is the meaning of not really good case?.you are not sure? And please I am not looking for an example for change in direction due to the action of two forces.

 

The example of a truck hitting a cyclist, that cannot be used as an example of perpendicular force. it doesn't stay perpendicular.

 

and there was only one force in the example i gave.

[Sisyphus]

It's the vector component in the original direction which doesn't change. The bike is still going at 10km/s (wow! fast bike!) in the direction it was to begin with, and ALSO has the speed of the truck in the perpendicular direction.

[Bignose]

spunnery, may I just ask in the search for common ground. What year of school are you in? How much math and physics study have you had? Has it been in a formal setting at school with homeowrk and exams or has it been self-taught?

 

The reason I ask -- and please don't take this as an insult because I and I suspect most of the rest of us on the forum want to help you as much as we can -- is that there seem to be some very fundamental issues that are not being understood or expressed correctly. The definition of force is pretty much the very first thing taught in a physics class. The independence of vector components is rather fundamental also.

 

So, answer those questions about your background and experience, and I think that we could probably provide much more informative and helpful answers. Thanks.

[spunnery]

spunnery, may I just ask in the search for common ground. What year of school are you in? How much math and physics study have you had? Has it been in a formal setting at school with homeowrk and exams or has it been self-taught?

 

The reason I ask -- and please don't take this as an insult because I and I suspect most of the rest of us on the forum want to help you as much as we can -- is that there seem to be some very fundamental issues that are not being understood or expressed correctly. The definition of force is pretty much the very first thing taught in a physics class. The independence of vector components is rather fundamental also.

 

So, answer those questions about your background and experience, and I think that we could probably provide much more informative and helpful answers. Thanks.

Many fundamental thinking have been changed by human being from the very begining of their evolution.Once they thought earth was flat. and so on.... So please read the whole thing carefully ,thoroughly and understand it(if you can) and reply.And please Talk for yourself,not for others

[Sisyphus]

Once they thought earth was flat.

 

Yes, and the ones who figured it out knew the difference between "flat" and "round."

[spunnery]

Yes, and the ones who figured it out knew the difference between "flat" and "round."

thats a fine answer.i am flattened .appreciate your humour sense.But iam not going to close the chapter

[spunnery]

The example of a truck hitting a cyclist, that cannot be used as an example of perpendicular force. it doesn't stay perpendicular.

 

and there was only one force in the example i gave.

It is an example.At any point of time until it hit,both the forces are perpendicular to each other.change in direction & speed is the result of two forces.

[Bignose]

spunnery, are you trying to tell me that your "revelation" that force and momentum are the same thing is akin to the revelation that the earth is not flat?

 

Or, are you trying to tell me that my saying that the members of this board want to help you is wrong, and that my ignorance is comparable to the people who once thought that the earth was flat?

 

Either way, I can prove you wrong. For the first, read a basic introduction to physics book. Force and momentum are different quantities. They are defined differently, and they describe different behavior. The onus is on you to prove to us that force and momentum are the same (best of luck).

 

For the second, when I started writing this, this thread is up to 37 posts, with 9 different forum members helping you. Please don't take this as condescending, it is not how I mean it, but this is a pretty basic physics topic. This probably goes back to the first part -- read a basic physics book -- but this thread's question was answered in post #2. over the next several posts, we gave several examples how the question was answered in post #2.

 

If you don't want our help -- if we are the human beings who have not changed our fundamental thinking -- then, frankly, you are free to leave. Or you are free to create your own entire system of physics where force and momentum are the same thing. But don't expect people to start converting over and shouting your praises unless your system of physics proves to be as easy and clear and consistent and as good at predicting phenomena as the current system is. In fact, it better be a lot better than the current system, because the current system does an awfully darn good job. I suspect it is almost incalculable how often the current system is used to make predictions today -- from lauching satellites to transmitting TV signals to building bridges -- and an almost innumerable number of other successful applications of the current system of physics -- quite a system you wish to buck here.

 

Also, don't expect me to spend my time trying to poke holes in your system by pointing out the inconsistencies (like making force and momentum the same.) So, whatever you choose to do, Good luck.

 

Perhaps the biggest point here is, every other person that replied in your thread has tried to show you one point of view, and you either don't understand it or just rejected it. Perhaps you are on to something new and grand here, or perhaps you should accept ours and the many thousands of exceptionally intelligent people who developed the system as we have it today expertise. And learn why the system is as it is today. Learn why momentum and force are defined the way they are. Learn why force and momentum as separate quantities.

 

At the very least, you need to learn the current system so you can show all of us non-thinking humans specifically why your system is better. So, you need to know all the details in-and-out of the current state, so you can give us loads of examples why your system is soooooo much better. Either you learn the current system to understand the replies you got in this thread or you learn the current system so you can demonstrate exactly where your system is going to be better. You have to study and learn the current system in both scenarios -- so pick up a introduction to physics book and start reading.

[spunnery]

spunnery, are you trying to tell me that your "revelation" that force and momentum are the same thing is akin to the revelation that the earth is not flat?

 

Or, are you trying to tell me that my saying that the members of this board want to help you is wrong, and that my ignorance is comparable to the people who once thought that the earth was flat?

 

Either way, I can prove you wrong. For the first, read a basic introduction to physics book. Force and momentum are different quantities. They are defined differently, and they describe different behavior. The onus is on you to prove to us that force and momentum are the same (best of luck).

 

For the second, when I started writing this, this thread is up to 37 posts, with 9 different forum members helping you. Please don't take this as condescending, it is not how I mean it, but this is a pretty basic physics topic. This probably goes back to the first part -- read a basic physics book -- but this thread's question was answered in post #2. over the next several posts, we gave several examples how the question was answered in post #2.

 

If you don't want our help -- if we are the human beings who have not changed our fundamental thinking -- then, frankly, you are free to leave. Or you are free to create your own entire system of physics where force and momentum are the same thing. But don't expect people to start converting over and shouting your praises unless your system of physics proves to be as easy and clear and consistent and as good at predicting phenomena as the current system is. In fact, it better be a lot better than the current system, because the current system does an awfully darn good job. I suspect it is almost incalculable how often the current system is used to make predictions today -- from lauching satellites to transmitting TV signals to building bridges -- and an almost innumerable number of other successful applications of the current system of physics -- quite a system you wish to buck here.

 

Also, don't expect me to spend my time trying to poke holes in your system by pointing out the inconsistencies (like making force and momentum the same.) So, whatever you choose to do, Good luck.

 

Perhaps the biggest point here is, every other person that replied in your thread has tried to show you one point of view, and you either don't understand it or just rejected it. Perhaps you are on to something new and grand here, or perhaps you should accept ours and the many thousands of exceptionally intelligent people who developed the system as we have it today expertise. And learn why the system is as it is today. Learn why momentum and force are defined the way they are. Learn why force and momentum as separate quantities.

 

At the very least, you need to learn the current system so you can show all of us non-thinking humans specifically why your system is better. So, you need to know all the details in-and-out of the current state, so you can give us loads of examples why your system is soooooo much better. Either you learn the current system to understand the replies you got in this thread or you learn the current system so you can demonstrate exactly where your system is going to be better. You have to study and learn the current system in both scenarios -- so pick up a introduction to physics book and start reading.

I still hope you are a single person(please don't use plural-and don't think always the rest of world is supporting you).

Let me discuss with you some fundamentals.

Force = mass x acceleration .

Does it means if there is no acceleration means no force?

[Bignose]

spunnery, regarding the 10 ton block: There has to be some force resisting you. Static friction immediately comes to mind. If there is no force resisting you at all, then you will move it. You or I can move a 10 ton block in deep space (where I assume no other forces act on the block). You may not move it very fast, but you will move it.

 

Edit: In case spunnery didn't put it back with his edits, he asked what if I pushed against a 10 ton block sitting on the ground. and I don't move it, didn't I apply a force?

 

But, if the 10 ton block is sitting on the ground on earth, there will be a static friction force resisting any force you put on it. The static friction force will be proportional to the normal force. The normal force is the force the block applies on the ground, in this case due to gravity. The gravitational force on a 10 ton block is obviously huge. The coefficient of friction would have to be measured but it would be a percentage of the normal force. Even a tiny percent of the normal force of a 10 ton block is huge. Unless the force you apply is larger than that frictional force, the net forces will sum to zero, hence, zero force, zero acceleration, zero work.

 

Here is the best example of this: You toss a ball in the air, and watch as it falls to the ground. The earth's gravity has applied a force to the ball, and moved the ball towards the earth. But, forces have to be equal and opposite. That ball has moved the earth closer to the ball. You can calculate this using Newton's law of gravity. It is going to be a very, very, very tiny amount. Like 10^-20 m. But, it has done it. This is a case of a small force -- the gravitational force of a ball -- moving a very large object, albiet an extraordinarily small amount.

 

Also, I don't think that the whole world is supporting me, but I do know the current state of Newtonian physics today. I am talking about the phsyics that has been developed for quite some time -- since before it was readily accepted that the world is round. And I know that anyone else who knows Newtonian physics is going to give you the same answers the other people who posted in this thread, and I, have given you. So, I am very comfortable speaking for everyone who knows how to do Newtonian physics properly.

[spunnery]

spunnery, regarding the 10 ton block: There has to be some force resisting you. Static friction immediately comes to mind. If there is no force resisting you at all, then you will move it. You or I can move a 10 ton block in deep space (where I assume no other forces act on the block). You may not move it very fast, but you will move it.

 

But, if the 10 ton block is sitting on the ground on earth, there will be a static friction force resisting any force you put on it. The static friction force will be proportional to the normal force. The normal force is the force the block applies on the ground, in this case due to gravity. The gravitational force on a 10 ton block is obviously huge. The coefficient of friction would have to be measured but it would be a percentage of the normal force. Even a tiny percent of the normal force of a 10 ton block is huge. Unless the force you apply is larger than that frictional force, the net forces will sum to zero, hence, zero force, zero acceleration, zero work.

 

Also, I don't think that the whole world is supporting me, but I do know the current state of Newtonian physics today. I am talking about the phsyics that has been developed for quite some time -- since before it was readily accepted that the world is round. And I know that anyone else who knows Newtonian physics is going to give you the same answers the other people who posted in this thread, and I, have given you. So, I am very comfortable speaking for everyone who knows how to do Newtonian physics properly.

Static frictional force is there! but where is acceleration due to that force?if no acceleration ,no force isn't it?

So please try to understand.There is forces acting on a body at rest or at uniform motion.

What we call force is actually ,the extra amount of force required to create an acceleration.

[Bignose]

Static friction resists whatever pushing force you apply. If you do not push with more than the static friction force, the total force on the block will be zero. You pushing + static friction = zero. No net force, no acceleration.

[spunnery]

Static friction resists whatever pushing force you apply. If you do not push with more than the static friction force, the total force on the block will be zero. You pushing + static friction = zero. No net force, no acceleration.

If Net force is zero,in both case.

case1.

You are not pushing.

case2.

You are pushing the stone.

 

Then the force to be exerted by a third person in both cases (imagine he is herculese-Strong),to move the stone would have been same.Isn't it?

 

So your effort in case 2 is not going to help him?

[Bignose]

So please try to understand.There is forces acting on a body at rest or at uniform motion.

 

 

At rest, the block sitting on the ground has two forces acting on it. The gravitional force pulling the block to the middle of the ground. And the force of the ground pushing back up on the block. These two forces are equal and opposite and sum to zero net force, that is why the block has no movement.

 

What happens if you start pushing on it? You apply a force to the side, but then static friction resists that force. Static friction is not always there -- you don't see block just slide about on their own. Friction is a resistance when a force is applied. So, the instant you apply a sideways force, friction attempts to neutralize that force. Friction can neutralize any sideways force up to a certain amount -- that amount is determined by the normal force and the coefficient of gravity. If you apply more sideways force than the maximum frictional force, then you will not have the forces balance to zero, and some net movement. But, if you do not apply more sideways pushing force than the frictional force, then the net forces again sum to zero. Zero force = zero acceleration.

 

However, a block in uniform motion in the absence of any other force, will continue indefinately. Again, we go all the way back to some of the first examples in this thread. A comet flying through deep space is assumed to have no forces acting on it. We assume no gravity, no drag from the few particles in space, etc. There is no force on that comet to ever slow it down -- it will have the same velocity forever. The same velocity, means the time derivative of velocity is zero, or in other words the acceleration is zero. No acceleration, no force. The equation works both ways.

 

Finally, back to the example of the car on a straight flat peice of highway with its cruise control on. This case is exactly like the comet. The only difference is that the comet has no forces on it at all, but this car example has the sum of the forces on it sum to zero. The drag from the air and the force the engine applies to keep the car moving and the friction in the tires and all the other forces sum to zero. That is what the cruise control is designed to do -- keep a constant speed indefinately. Again, constant velocity means that acceleration is zero. No acceleration, no net force.

 

Maybe the misunderstanding here is that nature is completely indifferent between the two situations. The first where there are no force or the second where forces are present, but they sum to zero. Nature does not differentiate between these two scenarios. They are the same, and the equations reflect that.

 

p.s. I am little tired of the "please try to understand" and "understand it (if you can)" I have tried not to insult your intelligence (and if I have I apologize) and would greatly appreciate it if you would stop insulting mine.

[Bignose]

If Net force is zero,in both case.

case1.

You are not pushing.

case2.

You are pushing the stone.

 

Then the force to be exerted by a third person in both cases (imagine he is herculese-Strong),to move the stone would have been same.Isn't it?

 

So your effort in case 2 is not going to help him?

 

If Hercules overcomes the static friction, then in case two, you will help him, even if it is a little tiny bit. Again, you can accelerate this 10 ton block in space. It may not be by a lot, just like your help compared to Hercules' will not be a lot, but it will help.

 

Let me create a small example then.

 

Let's say the maximum friction force is 1 million N. You can push with a force of 50 N. Hercules can push with a force of 1.5 million N.

 

You push the block yourself. 50 is not greater than the maximum friction force, so the friction force in this case is 50 N back. Zero net force.

 

Hercules pushs the block himself. 1.5 million is greater than the maximum friction, friction can only counteract with 1 million N. The net result? 0.5 million N in the direction Hercules is pushing.

 

You both push together at the same time. 1,500,050 N is greater than the maximum friction. The net result? 500,050 N in the direction you both are pushing.

 

Your meager contribution compared to Hercules is small, but it is there. And the net force that results is different than just Hercules himself.

[spunnery]

sorry I appologise

[Bignose]

Sorry i appologise

 

thank you.