If a magnet exerts force on a iron block (opposite and EQUAL), does a iron block also exerts force on magnet (via Newton's third law)? If yes then what magnetic property does it has to produce equal and opposite force on magnet considering that its not a ideal environment? If no then is it not the violation of newton's third law?
23124
Consider a system of the two identical positive point charges situated in free space (isolated from the influence of any other external fields) as shown in the attached diagram. Particle $1$ is at $(a,a,0)$ and particle $2$ is at $(0,a,0)$. Their velocities, at the considered instant of time, are as shown in the diagram ($\mathbf{v}_1$ along the $+x$ axis, $\mathbf{v}_2$ along the $+z$ axis).    Now, by applying the Biot-Savart law, we find that the magnetic field due to particle $2$ at the position of particle $1$ is along $+y$ axis, which means that the force acting on particle $1$ is along $+z$ axis according to Fleming’s left-hand rule. A similar analysis shows that there is no magnetic force on particle $2$ as the magnetic field of particle $1$ should vanish at positions (relative to particle $1$) located along its velocity vector.  Now, if we observe the net torque on the system of two particles about the $y$ axis then it is non-zero and is directed along the $-y$ axis. Here, there are no external forces or torques acting on the isolated two-particle system, and yet the net torque, as well as the net force on the particles, are nonzero. Why? Also, Newton's third law of motion seems to be broken in this scenario. Why?    Edit $1$  I have come to know from the responses that the electromagnetic field itself takes away some momentum and angular momentum about the considered axis. However, I think that if I consider only two charged particles as my system then the Abraham-Lorentz force can be assumed to be acting upon the system, and that is sufficient to make sure that we have considered the momentum being carried away by the electromagnetic field itself.   Even after considering the action of the Abraham-Lorentz force for the two-particle system, the scenario breaks both Newton's third law and the conservation of linear and angular momentum. This is because the Abraham Lorentz forces do not exactly counterbalance the force and the torques, on the two-particle system under consideration, due to the magnetic field.    Edit $2$  The previous edit was a result of confusion and misunderstanding on my part. The force associated with the momentum carried away by the electromagnetic field as a result of the electromagnetic interaction described in the question is the Lorentz force itself which simply doesn't obey the third law of motion. The Abraham-Lorentz force is a different story. It is associated with the momentum carried away by the radiation emitted by the accelerated charged particles. This is an additional force apart from the Lorentz force and corresponds to an additional carriage of momentum by the electromagnetic field. The momentum carried away by the electromagnetic field in correspondence with the Lorentz force doesn't correspond to radiation.
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?
31590
When a ball is thrown onto a wall, the ball exerts a force onto the wall. According to Newton's Third Law, the wall will exert an equal and opposite force to the ball. Thus, how would the ball be able to bounce back? Shouldn't it just slide down the wall?
72686
Working a problem with 2 pulleys and masses in class this week the professor at one point assumed that the tension on the two sides of a pulley would be different.  Every other time we've done a similar problem, we just assumed that the tension would be the same on both sides.  And I didn't understand his explanation of why we had to do it that way this time.  My question is when can we assume the tension on both sides of a rope are the same and when do we need to assume different tensions?
123462
For a long time I have wondered if there is a way to show that the rotational analogs of Newton's Laws are a direct consequence of just those laws, or are we adding more to them?  I understand mathematically that we take Newton's second law and do "r cross both sides," but that has always struck me as using more than just the 2nd law.  Here it matters where forces on the body are applied, but I don't see where Newton's Laws talk about points where forces are applied to a body. For translational motion it doesn't matter.  So are we adding a sort of "extra law" when we do this for rotation?  The only thing I can think of would be to "disassemble" an extended body into differential point masses and work with internal constraint forces that make the body rigid. If every mass is just a point mass it would get around the issue I'm having.  I've never seen any discussion along those lines, though.
81011
if i have a block of cotton and a block of iron each containing a weight of 100 kg when measured on a weighing machine, in reality which one is heaver than the other, which one is heavier and why?  This question was in my physics worksheet. The teacher gave the following answer: the apparent weight of both of them is the same, but the buoyant force of cotton is high since the volume of cotton is more than iron. Therefore, true weight of cotton is more. Does this answer make sense? What is the right answer?
17853
Recently, I  was pondering over the thought that is most of the elementary particles have intrinsic magnetism, then can gravity be just a weaker form of electromagnetic attraction? But decided the idea was silly.    But I then googled it and found  article. Is this idea really compatible with other theories as the article mentions? Is there any chance of this proposition being true?
29610
I know plus pushes another plus away, but why, really, do they do that? On the other hand, molecules of the same type are attracted to each other. I find that weird.  I do know some stuff about four universal forces. But why in general the general "rule" is that opposite charges pull each other?   Yes, I do realize this could be connected to very basic stuff that science is still trying to figure out, and can be traced to the Higgs,  but still, there must be something to tell.
37082
I haven't touched Physics and Math (especially continuous Math) for a long time, so please bear with me.  In essence, I'm going over a few Physics lectures, one which tries to calculate the Force exerted by uniform magnetic field on a semi circular current carrying wire.  The mathematics that puzzles me is this, that:  $$ \sin(d \phi) \thickapprox d\phi $$  where $d\phi$ is very small. .
68853
I am a student of class 9. When I was going through magnetism and read that an earth is a magnet I got some doubts. My question is: is earth really a magnet? Doesn anyone have any proof that earth is a magnet? Is there a magnetic core at the center of the earth? Has anyone reached the core of the earth?
49748
Is Newton's third law valid at the General Relativity?  Newton's second law, the force exerted by body 2 on body 1 is: $$F_{12}$$ The force exerted by body 1 on body 2 is: $$F_{21}$$  According to Newton's third law, the force that body 2 exerts on body 1 is equal and opposite to the force that body 1 exerts on body 2: $$F_{12}=-F_{21}$$
70064
I'm having trouble understand the concepts for this problem. Here's the problem:     A block is placed on a plane inclined at angle $\theta$. The coefficient of friction between the block and the plane is $\mu = \tan \theta$. The block is given a kick so that it initially moves with speed $V $horizontally along the plane (that is, in the direction perpendicular to the direction pointing straight down the plane). What is the speed of the block after a very long time?   We can see that $F_x = mg\sin \theta - mg\cos (\theta )\mu = 0$, if we gave the block an initial velocity along the plane, it should be subjected to a friction force opposite its velocity, where $f = mg \cos \theta \tan \theta = mg\sin \theta$   This however, is the answer my book gave:     The normal force from the plane is $N = mg \cos \mu$. Therefore, the friction force on   the block is $N = (\tan \mu)N = mg \sin \mu$. This force acts in the direction opposite to   the motion. The block also feels the gravitational force of $mg \sin \theta$ pointing down the   plane.   Because the magnitudes of the friction force and the gravitational force along the   plane are equal, the acceleration along the direction of motion equals the negative   of the acceleration in the direction down the plane. Therefore, in a small increment   of time, the speed that the block loses along its direction of motion exactly equals   the speed that it gains in the direction down the plane. Letting v be the speed of   the block, and letting vy be the component of the velocity in the direction down the   plane, we therefore have $$v + vy = C$$   where $C$ is a constant. $C$ is given by its initial value, which is $V + 0 = V$ . The final value of $C$ is $V_f + V_f = 2V_f$ (where $V_f$ is the final speed of the block), because the   block is essentially moving straight down the plane after a very long time. Therefore,   $2V_f = V \rightarrow V_f = \frac{V}{2}$   I don't really understand what this is trying to say. The bolded part is what's giving me problems. I think it just may be poorly written, I think I need a clearer explanation.
8993
Need help in understanding the direction of magnetic force in the magnetic field!Totally confused by directions.  Why is it that magnetic force is perpendicular to the direction of magnetic field and velocity of charged particle. Why is it(force) not in the same direction as the magnetuc field
118144
From what I understand of the idea behind , they use .  I also understand that it uses Lenz's law and eddy currents. And that the hendo-hoverboards only work in non-ferromagnetic material.   From what I re-call, Lenz's law states that eddy currents are created when magnets are moved relative to conductive materials. In particular, lenz's law states that eddy currents are formed when there is a change in magnetic flux. So they used magnetic field architecture.   Magnetic Field Architecture (MFA) is a design where there are 4 electromagnets on the base of the board that propels on non-ferromagnetic material.   However, I don't understand how that works? How do they calculate the gravitational pull such that the MFA exerts more force to over come that gravitational pull?
122090
I recently bought some , considered to be the world's best selling desk toy. Essentially, they are little, spherical magnets that can form interesting shapes when a bunch of them are used together.  After playing around with these buckyballs for a while, I wondered: "Can these guys ever lose their magnetism?" Then I went a step further and thought, "How are magnets affected by the 2nd law of thermodynamics?"  So, how are magnets affected by the 2nd law of thermodynamics? Do they break down and lose their magnetism over time (like iron rusts over time)?
14270
Question: Find the mass M of the hanging block in the following figure which will prevent the smaller block from slipping over the triangular block. All the surfaces are frictionless and the strings and the pulleys are light.    What I did: Considering that M-mass block is moving downwards, I assumed that the string would transmit force $Mg$ to the inclined plane. Thus the inclined plane would move forward with acceleration $\frac{Mg}{M^-}$ towards the right, while the m-mass block would move backward, in a horizontal direction, with the same acceleration. Calculating components, the acceleration up the incline would be $\frac{Mg}{M^-}\cos \alpha$. The acceleration of the block on its own would be $g\sin \alpha$. Equating the two, I got $M = M^-\tan \alpha$  New approach (considering horizontal component of normal force exerted by small block) Considering the fact that the normal force exerted by the wedge on the block to be $mg\cos \alpha$, the block exerts an equal force on the wedge. The horizontal component of this normal force will be $mg\cos \alpha\sin \alpha$. Thus the acceleration of the wedge will be $$\frac{Mg - m\cos \alpha\sin \alpha}{M^-+m}$$ This should be equal to the downward acceleration of the small block: $g\sin \alpha$. Equation the two and solving for $M$, I got: $$M = \sin \alpha(M^- + m) + m\cos \alpha\sin \alpha$$ Still not the correct answer: $\frac{M^- + m}{\cot \alpha -1}$
22128
Does a charged rod or a shell have a magnetic potential energy when it is kept in a uniform magnetic field?  Also, can anyone quantitatively explain why a wire loop carrying current would tend to be circular?