I have seen  on the site, but that was kind of different in its essence — it was aimed at asking the solution of a particular problem, while I am having trouble conceptualizing the idea of Work. Here's my understanding —  If I push a wall, it doesn't move. There is no displacement; but I DO lose some energy — a force will be applied. The wall does not move because the force that is applied is not sufficient to overcome the 'adhesive' or 'structural' forces there are at the edges of the wall and keep the wall joined to the house. Had they (and friction) not been there, the wall would have moved (though slightly). Does it not then follow that I am indeed doing work on the wall, but it simply doesn't move because other forces are doing work on it too, and my work is not enough to overcome them? It would then be reasonable to say that no net work is being done on the wall, but I see everyone saying that I, for myself, will not be doing any work at all because I will not be displacing the wall, in such a scenario.  What's wrong with my understanding?
12097
I read the definition of  as  $$W ~=~ \vec{F} \cdot \vec{d}$$  $$\text{ Work  =  (Force) $\cdot$ (Distance)}.$$ If a book is there on the table, no work is done as no distance is covered. If I hold up a book in my hand and my arm is stretched, if no work is being done, where is my energy going?
13179
I'm having some trouble understanding the concept of negative work. For example, my book says that if I lower a box to the ground, the box does positive work on my hands and my hands do negative work on the box. So, if work occurs when a force causes displacement, how does negative work happen? Are my hands displacing anything?
28738
I was just wondering... I believe that if a car travelling 50 miles per hour crashes into a wall, the result should be the same as crashing to another car also travelling 50 miles per hour (but in the other direction of course)  Is this true? Why is that?
22713
We want to knock the kitchen and dining room into 1 room and I am hoping someone can help tell me if the highlighted wall is non load bearing:
11750
What exactly is ? My book confuses me:     a force can lift an object to a height h, or it can accelerate an object through gravity. In all these cases, a force displaces an object and change the object's total energy.   The examples it gives confuse me. On one hand, there is lifting and on, accelerating through gravity.   I can imagine how lifting will change total energy (kinetic + potential). It essentially gives it more potential energy, and does not take from it any kinetic energy. But just dropping an object and let gravity do the work does not seem to me to increase total energy. Because the total amounts of kinetic and potential energy should be equal.  If just let drop, the object will gain kinetic and lose some potential. Not really anything added to the total energy.
47188
I did lot of searching but couldn't find any textbook nor any webpage which could clarify my doubt. Maybe my doubt is insanely stupid and I was dumb for not realizing it at the first place.  The negative of the work done by the electrostatic field in bringing a charge from infinity to a point is called electric potential.   Let us assume that there is a positive charge at the origin. Let work done by the external force to bring a positive from infinity to a point P close to the origin be W. And hence work done by the field to bring a positive charge from infinity to the point P will be -W.  If I did work W to bring the charge from infinity or if the field brought the charge from infinity, either way the change in potential energy will be same.  In case of work done by the field, we say that the work done is stored in the form of electrostatic potential energy.  In case of work done by the external force, we say that the work done was positive and the energy was taken by some external source.  In the above case, I did work W in bringing it &amp; the field did work -W on the charge trying to push it away so I did positive work of W &amp; the field did negative work of W. We can say that the work done by the field was stored as potential energy.   Where did the work done by the external force (me) go?  I can summarize the whole doubt in the following line: I did work W to bring an charge towards another unlike charge, and therefore the field also did work -W, the net work done on the charge is 0. But there is still a change in potential energy. Why did the potential energy change? Isn't conservation of energy being violated here?  Please clarify my doubt (I do understand that there is a horrible conceptual error in one of my arguments but I do not know which one it is). If I am not wrong this has nothing to do with electrostatics rather has to deal with field theory/inverse square law. I believe I will be encountering the same problem again when I would be studying another force, maybe gravitational, which obeys inverse square law.  Thank You
115118
If using the surface of the earth as a reference point how much work is needed for gravity to pull me to the center. Is it negative infinity or am I wrong? Also is a single value of potential meaningless. Does it represent anything? Do you at least need a potential difference for it to represent work done? I'm extremely confused about potential and potential energy.
98721
Just a clarification question based on an example I read about.      Can normal force do work on an object?   The answer is yes, with an example being a person jumping. The normal force causes work to be done.  However, I'm wondering, is that actually normal force, or is that the reaction force from applying force to the ground? There is a difference between the reaction force and normal force. I'm not sure if technically that example is correct. If it isn't, can someone provide a different one where normal force does do work?
10731
I have asked a question on I  pushing the wall,where the force of me is not zero but as per the formula F=m.a,the force is zero and then I got the answer , it is because here the net force is acting on the body.But I a doubt that then a body of mass 5kg and moving with an acceleration 2m/s^2 will experience a force = 10N,Is in this case also the net force acting? Or  the net force is acting only when the body doesn't move? If this is correct then my question why?
59889
I am something of a dilettante in physics, so please forgive me if the answer to this question is painfully obvious. The question is simple, can something that theoretically has no mass exert a force. I have been tossing around this and other similar questions in my head for a while now and have not really found any concrete answers to my inquiry. I am thinking about how light seems to be able to push objects but yet has no mass, however I expanded the question to be more encompassing in hopes of further learning.
82301
Intro:  In completing , he presents an experiment (go to 42:44) which leaves me baffled.    Experiment:  (I recommend watching the video; see link above.)   There is a $2$ kg block with 2 identical strings attached to it: one at the top, the other at the bottom. The top string is attached to a "ceiling", and the bottom to a "floor". Professor Lewin "stretches" the system (by pulling on the bottom string) with the block not accelerating. One string snaps.     Prediction:   Initially, the top string has a tension of approximately $20$ N, to counter the force of gravity. The bottom string has no tension at all. Then, when Lewin pulls the bottom string, it gains some tension $n$ N. To counter act the force exerted by the bottom string, the top string exerts now $20 + n$ N. I assume that the string with more force will give out sooner, leading me to conclude that the top string will break.     Results:  (This was conducted by Lewin, not me; see link above.)   Trial 1: Bottom string breaks. Trial 2: Top string breaks. Trial 3: Bottom string breaks.     Additional Notes:  The results don't seem consistent. If I was right, I'd expect all 3 experiments to be right; conversely, if I was wrong, I'd expect all 3 experiments wrong, with one exception: the results are more-less random and one result isn't preferred over the other.    Question:        Why was my prediction incorrect?   Was there a flaw in my logic?   Why were the results inconsistent?
41160
As I am seeing this,  the man and boat will have different displacement from ground frame,  so there should be a net work done by friction .  The books says,  total work done by friction is zero when friction is static and internal to system. Please explain..
5872
I am trying to teach myself some basic physics, here is something I do not really understand about the definition of :  When moving from $a$ to $b$ (in one dimension), the work done is defined to be   $$ W = \int_{a}^{b} F dx $$  Now, say, I lift something up from the floor to a table covering a distance $h$. The work done is supposed to be $mgh$. This result is obtained by setting $F = mg$ in the equation above, which is the force exerted by gravity on the object. However, gravity is not the only force acting upon the object. What about the force used by me to lift the object, why does it not enter the equation?
33453
For a constant force, $P=Fv$. I understand the mathematical derivation of this, but this seems to me, intuitively, to be nonsense. I feel that my discomfort with this comes from a fundamental misunderstanding of force and Newton's Second Law, so I'm not really looking for any mathematical explanation. So, to begin:  How is it that a constant force does not add energy to a system at a fixed rate? Consider a rocket burning a fuel at a constant rate. The chemical potential energy should be converted to kinetic energy at a constant rate, that is, $(1/2)mv^2$ should be increase linearly. The magnitude of the velocity of the rocket would then increase at a less than linear rate, implying a nonconstant acceleration and therefore, a nonconstant force/thrust (F=ma).  If force is indeed a "push or a pull," shouldn't that constant rate of burning of fuel yield a constant "push or pull" as well? Clearly not, so I would have to think that, somehow, a given force applied to a certain object at rest would in some way be different than that a force of the same magnitude being applied to that same object in motion. In this sense, is force merely a mathematical construct? What does it tangibly mean, in physical terms? Would a given force acting upon me "feel" differently to me (in terms of tug) as I am moving at differing velocities?  Force being defined as a "push or pull," which is how it has been taught in my high school class, seems rather "handwavy," and maybe that's the issue. It's been troubling me for a couple of weeks and my teacher hasn't really been able to help, so thanks!
50056
As a child, I imagined this device, which may seem to rotate indefinitely. I have two questions.   Is this perpetual motion machine already known? If it is, could you please give some references? What is the exact mechanism that makes it stop? By this, I mean an explanation, not simply "because it would break law of energy conservation". Of course energy conservation is true and this machine cannot work indefinitely. But for any known (presumed) perpetual mobile, there was an explanation, usually based on showing that the force generating the motion is . For example, Stevin obtained the laws of the inclined plane from the perpetual motion device     I would like to make some observations.   I don't try to convince anyone that it will move forever because I don't believe in breaking the energy conservation. It is true that , and nowadays some who think that there may be  in MWI believe, but I don't. But I don't consider an enough explanation simply to refer to the energy conservation. I am interested in an explanation showing exactly how the magnetic forces making it rotate, are balanced.  If the forces are balanced, only then friction will make it slow down and stop. I don't think that we can explain only by referring to friction, which in principle can be made as small as needed. There has to be a balance of forces. Why spending time trying to understand or explain something that admittedly can't work? Well, even though perpetual motion machines cannot actually work, I think they may be interesting as puzzles.
79130
Can anybody please tell me if magnetism is a conservative force or if there is a field associated with it? How to reason? One thing I know is that the work done by a magnetic force is equal to $0$.
35933
My questions might seem naive as I haven't plunged into the mathematical descriptions, but wormholes are interesting even if I don't actually know them :)  First of all, is wormhole making two possible paths betwwen points (like the tunnel in most visualisations) or is it just making two points beside each other like in the game Portal? Of course, second case can be bent into a tunnel, but there would be nothing special about tunnel part and no preferred way to divide into "normal" and "tunnel" part of spacetime.  My main questions are these:   Is momentum conserved? Is kinetic energy conserved? How does potential energy work?   To elaborate... In the game Portal you can fall into floor and fly out of the wall or floor elsewhere with the same speed, but another direction (normal to the portal). So momentum is not conserved, but kinetic energy is. Is that how it would actually work? Where does the momentum go then?  And does it really allow you to increase your potential energy while retaining kinetic? It would seem fair to take away some kinetic energy if you are put in a region where you have more potential energy.  Either way is the change in energy non-continuous like in the game and discussion that's linked below? Or are there just more than one way to move through but the change in potential energy is smooth in any of those? That would mean more potential equilibrium points though...  Similar questions has been discussed , is it correct about how the falling guys gets a lot of energy (in form of a potential one) by draining it from the mouths?