I know that this is a total novice question. When I push a book from point A to point B, a force is applied by me. The book has mass and some acceleration was also achieved in this example. I recently read about the fundamental forces of nature. They included Gravitation, Electromagnetism, Strong interaction, and weak interaction.  I have no deep knowledge regarding any of the 4 forces. A simple explanation would be appreciated. My question is :     In the act of pushing a book, which of the 4 fundamental forces of nature come in the picture? Which one force could I relate to this event?
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If you've ever been annoyingly poked by a geek, you might be familiar with the semi-nerdy obnoxious response of      "I'm not actually touching you! The electrons in the atoms of my   skin are just getting really close to yours!"   Expanding on this a little bit, it seems the obnoxious geek is right. After all, consider Zeno's paradox. Every time you try to touch two objects together, you have to get them halfway there, then quarter-way, etc. In other words, there's always a infinitesimal distance in between the two objects.   Atoms don't "touch" each other; even the protons and neutrons in the nucleus of an atom aren't "touching" each other.  So what does it mean for two objects to touch each other?   Are atoms that join to form a molecule "touching"? I suppose the atoms are touching, because their is some overlap, but the subatomic particles are just whizzing around avoiding each other. If this is the case, should "touching" just be defined relative to some context? I.e, if I touch your hand, our hands are touching, but unless you pick up some of my DNA, the molecules in our hands aren't touching? And since the molecules aren't changing, the atoms aren't touching either?  Is there really no such thing as "touching"?
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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.
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There are several conditions that must be met in order for a force to be . One of them is that the curl of that force must be equal to zero? What is the physical intuition behind this? If you can, please explain it to me via the magnetic force fields because i have read that time-varying magnetic fields are not conservative because they do not meet that condition.I do not understand this.
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I apologize if this seems like a quack question, but I need some insights by those who know much more than me in Physics.  Anyway, the gravitational "force" (not really a force) is a manifestation of the curvature of space-time, caused due to presence of mass. Suppose I conjecture that ANY force (electroweak, strong...) is also a manifestation of some property of space-time effected by "something" (as in mass in the case of gravity, and different for different types of forces).  So is there any blatant fault with this line of thought? (I'm asking for blatant faults, since it's a wild supposition anyway)
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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 $0$.
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Is it a coincidence that there are four fundamental forces and four spacetime dimensions ? Does a universe with three spacetime dimension contain four fundamental forces? Can magnetism  be realized in three dimensional spacetime?  Edit 1: Thanks alot for the answer. I'm a first year undergrad student so this may seem naive. If there is a symmetry that mixes spacetime symmetries and internal symmetries of the theory (e.g. gauge symmetry) then there might be ways that spacetime geometry have effects on the particle spectrum and interactions of the theory so you can describe things in geometrical manner . The mechanisms that lead to the structure of spacetime may explain why there are four forces.
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Possible Duplicate:          I am an engineer who loves to read science fiction books especially when there's more science than fiction but usually I see that I lack the knowledge behind many of the relativity concepts in the novels. I've always felt curiosity in relativity so I decided that it was the time to buy an introductory book. I went to amazon and checked that there are dozens of "Introduction to general relativity" books in there. So here's my question: What book would you recommend to someone not matematician nor physicist but with (some) mathematical background as an introduction to relativity?
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You can have two electrons that experience each other's force by the exchange of photons (i.e. the electromagnetic force). Yet if you compress them really strongly, the electromagnetic interaction will no longer be the main force pushing them apart to balance the force that pushes them towards each other. Instead, you get a a repulsive force as a consequence of the Pauli exclusion principle. As I have read so far, this seems like a "force" that is completely separate from the other well known forces like the strong, electroweak and gravitational interaction (even though the graviton hasn't been observed so far).   So my question is: is Pauli-repulsion a phenomenon that has also not yet been explained in terms of any of the three other forces that we know of?  Note: does this apply to degenerate pressure too (which was explained to me as $\Delta p$ increasing because $\Delta x$ became smaller because the particles are confined to a smaller space (Heisenberg u.p.), as is what happens when stars collapse)?
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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?
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My friend and I were arguing about this and I was wondering if someone out there could settle this for us.    Basically, he and I were walking to buy some stamps. When we were on our return trip he made the assertion that when I returned to my desk, which is where our trip began, I would have accomplished zero "net work". That is, utilizing our admittedly simple understanding of work from Wikipedia:       In physics, a force is said to do work when it acts on a body, and there is a displacement of the point of application in the direction of the force.   when I return to my departure point, that is my desk, the total displacement would be zero and using the definition from Wikipedia that $W = Fd$ and $d$ is displacement, no work was done. Intuitively, I suggested that there were two quantities of work done, one quantity of work from my desk to the shop and one quantity of work from the shop to my desk, but when I look at some decriptions of a displacement vector, I feel like the two displacements may also cancel each other out. Can someone help us sort this out?    Thanks in advance for the help!
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Firstly I think shades of this question have appeared elsewhere (like , or ).  Hopefully mine is a slightly different take on it.  If I'm just being thick please correct me.  We always hear about the force of gravity being the odd-one-out of the four forces.  And this argument, whenever it's presented in popular science at least, always hinges on the relative strength of the forces.  Or for a more in depth picture .  But, having had a single, brief semester studying general relativity, I'm struggling to see how it is viewed as a force at all.  A force, as I understand it, involves the interaction of matter particles with each other via a field.  An energy quantisation of the field is the force carrying particle of the field.  In the case of gravity though, particles don't interact with one another in this way.  General relativity describes how space-time is distorted by energy.  So what looked to everyone before Einstein like two orbiting celestial bodies, bound by some long distance force was actually two lumps of energy distorting space-time enough to make their paths through 3D space elliptical.   Yet theorists are still very concerned with "uniting the 4 forces".  Even though that pesky 4th force has been well described by distortions in space time.  Is there a reason for this that is understandable to a recent physics graduate like myself?     My main points of confusion:   Why is gravity still viewed as a force? Is the interaction of particles with space time the force-like interaction? Is space-time the force field? If particles not experiencing EM/weak/strong forces merely follow straight lines in higher-dimensional space (what I understand geodesics to be) then how can there be a 4th force acting on them?     Thanks to anyone who can help shed some light on this for me!
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From Wikipedia: The work done by a constant force of magnitude F on a point that moves a displacement d in the direction of the force is the product: $$W = Fd.$$  If I lift some object from a ground, the force to be put in above equation is the gravitational force $mg$.   But while I am moving the object upwards, against the gravity, I must pull the object with greater force than $mg$, right? So the net force is $F_{myforce}-mg$ which results in object being lifted. But this is not the case. Why? Does it matter how strongly I pull the object?  What work will I do if I move this object in absence of gravity (in space)? Will work done be zero or not?
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My understanding about  is a force that its work is independent of path such that we can construct another form of the work called potential to make our life easier.  For friction, if I start from microscopic point of view, it should be the macroscopic effect of the electric force or gravity which are both conservative force.  Why do we initially have description by conservative forces (electric/gravity force) but end up with a macroscopic description of nonconservative force(friction)?
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I'm interested in learning physics. I do realize that the subject is large and that it would be easier if I had a specific area of interest. However, I do not. I suppose I want to learn about the fundamentals of it all; the axioms that combine all physics fields. Or, in other words, a high school physics class.   Specifically, a book or series of videos would be helpful. I looked over MIT and unfortunately the material wasn't for me. I don't mean to be "picky" so I am not completely ruling out any resource just yet.   Thanks in advance.
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As a 8th grader I am still a newbie at science and I have problems understanding the forces that I can not imagine and one of these "forces" is the moment.  We are told that,  $$\text{moment}= Nm$$ but how can a certain force (i.e. $N$) be applied when there is $m$? How does it depend on the length of the considered object?  And how can 1 moment be defined on the basis of that representation?  And what would be the effect if the moment value is increased by the newton part as opposed to the effect when the value is increased by the length part.  Or is the result the same in both cases?
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I know this has been asked around, my question is a bit more specialized towards my personal problem.  If I have an object the magnitude of the weight is usually equal to the normal force, right?   I could be mistaken but from what I have read the normal force is the force the object is feeling opposite to the $(mass*gravity)$. If that is the case, and I put my hand on the object does my Force get added to the object's weight and thus the normal force of that object increases? Therefore if I keep adding hands to the object will the normal force keep compensating?   Also is the normal force the negative charged electrons repelling each other (electromagnetism)?
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A problem related to an interesting  Casimir configuration.   I have the following configuration, related to a modified Casimir experiment.  We have two parallel metal plates and an  orthogonal  metal plate connecting the two parallel plates. Note that this is very close to the experimental setup of the original Casimir experiment,  except for the orthogonal plate (connecting the two parallel plates at one end).   I would like to know all the Casimir  forces that exist in this configuration.  For clarification, you can see the following picture:    My naive intuition could be incorrect, but my impression is that the asymmetric radiation  pressure due to quantum fluctuations would lead to the emergence of a certain force (parallel to the parallel plates), but I don't know if the QFT / QED calculations justify my intuition (where in fact  these virtual particles are just an intuitive representation of links in Feynman diagrams, linked to terms in infinite perturbation series).       Closely following the arguments in these two papers, that force mentioned above does indeed exist (for the three plate system mentioned above).  I hope somebody here can quickly settle this problem, so I don't spend a long time digging for an answer. Thanks.