# Tag Info

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Firstly its the potential energy of the earth-object system as the two answers have said. "Potential energy of the object" is a loosely spoken phrase for the same for things happening on the surface of the earth where $g$ is taken to be a constant.Secondly work is not done by a person. Work is done by a force.There is an important thing you need to know. ...

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Yes so-called pseudo forces do work and if they were to be describable as a conservative force, then yes the corresponding mechanical energy would be conserved. The best example I can find is the gravitational pull we feel at the surface of the Earth. It is in fact the sum of the "true" gravitational force owing to Newton's law of gravitation and the, ...

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My suspicion is that the output of your first capacitor still has a 2.8 V peak-to-peak 60 Hz ripple on it. There is always some level of ripple out of the usual rectifier + capacitor DC power supply. Putting a diode between the first and second capacitors creates a "peak detector" that samples the highest points of this ripple at +1.4 V above your 160 V ...

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To change the velocity of the ball a force must be applied against it. In your example the force is applied by the wall on the ball and this force does work. And this work which is not same in all frames of reference, according to your example, gets completely converted to heat.To explain it simply, lets say that the ball is deformed and becomes completely ...

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Timaeus has given the full technical answer: the kinetic energy of the wall itself changes a tiny bit. Since kinetic energy scales as $v^2$, this is totally negligible in the first case (where the wall starts with $v = 0$) but actually significant in the second case (where the wall starts with $v = 2$), and that's where the missing energy goes. Luckily, in ...

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Imagine a ball ($mass= 1kg$) moving at a velocity $2 m/s$ towards a wall. When it hits the wall, it suddenly stops, thereby liberating all its KE as heat. Here, $Initial K.E. = (1/2)*m*v^2 = 2J$, and final KE is obviously zero. So heat liberated ($Final KE - Initial KE$) equals $2J$. Now, suppose I hop on to a car moving at $2 m/s$ towards the oncoming ball ...

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Initially your ball has some energy ($2J$) and some momentum ($2Ns$). And the wall has some energy ($0J$) and some momentum ($0Ns$). And there is some internal energy, $U=U_0,$ the thing that heat increases. Afterwards the ball has some energy ($0J$) and some momentum ($0Ns$). And the wall has some energy ($0J$) and some momentum ($2Ns$). And there is some ...

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In the car frame the ball initially has 8J of kinetic energy relative to you, however it has only 2J of kinetic energy relative to the wall which is also moving in the cars frame.

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Part of your problem comes from thinking that the potential energy is somehow located in or a property of the person alone. And the way the subject is usually introduced could easily lead you to think that, but it's not right. The potential energy is a property of the person-Earth system. In fact all potential energies are properties of systems of ...

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Before explosion the bomb is at rest. Its total momentum is zero. As it explodes, it breaks into many parts of masses $m_1,m_2,m_3$ etc which fly of in different directions with velocities $v_1,v_2, v_3$ etc. these diff parts have different momenta $m_1v_1,m_2v_2, m_3v_3$,etc. For eg,- If the bomb explodes in two parts then both of them fly into opposite ...

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Connecting two perfect capacitors like that would be like connecting two perfect but different voltage sources; you would get a hypothetical explosion. In real life, every capacitor has inductance and resistance. So, as the current built up between the two capacitors, you'd heat up the wire between the capacitors as well as the capacitors themselves. If the ...

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There's no work done for a person climbing upstairs because the energy is converted to PE within system only. The person is the system. How true is the above statement? I think it's true enough. You do work on a brick when you lift it up. You add energy to it, and we call this energy gravitational potential energy. Then when you drop the brick this ...

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The above statement is not correct. First of all, you need to work against the force of friction while climbing stairs.So the energy is not entirely converted to PE.Rather a portion of it is dissipated. Secondly, even if we leave out friction, the basic flaw of the statement lies in the part: " the energy is converted to PE within system only. The person ...

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To find the minimum velocity at the bottom-most point, we find the minimum velocity at the uppermost point. This minimum velocity is the one such that the centripetal force is equal to the force of gravity. Any lower and gravity will pull the object down and out of the loop, any higher and a faster velocity would be required to generate it (thus, not a ...

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A tension less than zero isn't really physical; this is the point where the string stops being taught and the object doesn't make a complete circle. Therefore, when finding the minimum velocity for an object to make it around a loop, we solve for when the tension at the top is zero as it is the minimum possible tension for the object to keep going in a ...

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Considering 'space-time', rather than space and time, time is essentially just a 4th axis along which we can move (generally at a rate of one second per second in the positive direction); the other three being the familiar x, y and z Sending something backwards through time (if possible) would not involve destroying energy in the present and creating it ...

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Conservation of energy/mass is the result of a symmetry called time shift symmetry, and if this symmetry is broken energy/mass will no longer be conserved. It is far from obvious that time shift symmetry would be preserved if closed timelike curves were possible, so you can't use conservation of energy as an argument that time travel is impossible.

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Most time machines seem to require having exotic matter which has negative energy density, so perhaps you can send back some negative energy and some positive energy. Creating mass isn't an issue, mass isn't conserved and really that's because the mass of a system isn't the sum of the masses of the parts. And there are other options. For instance, if you ...

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then the created pions will be at rest correct? Well, they will be at rest in the Center of Momentum frame. But that is not the frame of reference that your problem is stated in. Momentum is conserved, which tells you that you have written the pion four-vectors incorrectly.

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Technically, the energy of a system is conserved. This is a subtle, but important, distinction from the energy being constant. Conservation is different from constancy in that energy can move in and out of a system and can change forms, but it is neither created nor destroyed. An expanded formula would look like this: ...

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There is a reason physics starts with kinematics, description of motion and evolution is what it is about and once you throw in the causes you get dynamics, which is everything. It is not obvious that energy is secondary at all. And I dispute it. How can you tell you have something? Because it interacts in certain ways (dynamics) or it has the capacity to ...

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You are correct that global energy isn't conserved. But it is actually worse than that. Since energy is frame dependent and there isn't necessarily a global frame, then there isn't even an objective number called total energy that can change from moment to moment. So there just isn't a thing called total energy. And energy isn't free, to get some energy ...

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Energy is not conserved in basic general relativity because there is no energy associated to the gravitational field. If you associate some energy to it (via for instance the Einstein pseudotensor), you can recover energy conservation, the lost energy just being stored in the form of the GR equivalent of gravitational potential energy.

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Energy is conserved, but if you ignore some kinds of energy then it will look like it isn't conserved. You can imagine a really big disk with some radial pointing two by fours attached at the one o'clock, two o'clock etcetera positions then attach springs to each two by four with the spring pointing in the clockwise/counter-clockwise directions. Add a nice ...

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As one of the comments mentions, it is simpler to consider a linear case. Dropping a body of mass $m$ on one moving with mass $M$ and velocity $v$ is essentially considered the instantaneous transformation $M \to M + m$. Momentum must be conserved in the collision, but the mass of the system effectively increases, producing a smaller kinetic energy:  ...

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Following from the comments... We've established that the upper fluid is moving, suggesting that heat transfer into it is convective in nature. We've also got that the lower fluid is being used to convectively heat the sheet. So that fluid is moving as well (convection being heat transfer by motion of a fluid). So you've got basically identical boundary ...

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Is it correctly understood that energy is continuously put into the system, in order to maintain the orbit? And that gravity is thus an infinite source of energy? Consider the general case of one particle orbiting another in an ellipse (this is general because we can a always reduce the two body problem to an effective one body problem, and the general ...

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I think you need to read up a bit on vectors and scalars, how we define things like acceleration. Vectors are physical quantities that have a magnitude and a direction. Velocity is a vector (speed is its magnitude). Acceleration is also a vector. Acceleration is defined as the rate of change of velocity, basically it measures how velocity changes with ...

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As pointed out in some comment, electrons are being accelerated in the process of charge. This generates electromagnetic radiation. Try doing the calculation using Poynting vector, the way Maxwell defined electromagnetic energy.

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Because in the second scenario you described, the exhaust gases from the rocket fly off at high speed into space. This is where the extra energy goes. A better alternative to get circular motion of the satellite with the earth removed, would be a second satellite, connected to the first satellite with a long cable. If, for example, both satelittes have the ...

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Historically, conservation of energy may have been discovered by Julius Robert Mayer in 1842. When he was a youngster he tried to build a water wheel that drove an Archimedean screw to lift water back up to the top of the wheel and keep it turning. He found this to be impossible. The lesson stayed with him 'til later in life he became a doctor and studied ...

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Can I attribute the conservation of mechanical energy to the power of maths, especially vector calculus? No. Is this the true story behind the process during which people discover conservation of mechanical energy? No, energy conservation was historically a long debate over centuries. Is there a better way of arriving at the conclusion? For ...

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I was not able to convince him that this propulsion drive cannot work due to conservation of momentum. Am I wrong about that? No, you are not wrong. It's clear that the engine cannot work because of momentum conservation. It's basically just a fixed double pendulum. Why should there be any positive momentum in any direction after one full circle? ...

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Given the persistence of this kind of thing, maybe determining the misconceptions underlying it are not so easy to determine and resolve. [Given that we're talking about physics students, I guess it's fair to them to sort this out rather than ignore as one might otherwise.] For my money, I'd ask whether within each part of the mechanism Newton's Third Law ...

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The answer is simply yes. As long as conservation laws are satisfied. Nothing is to be regarded as $0$ energy, $0$ mass, $0$ charge, and so on. Keep in mind that mass is a positive form of energy, while interacting energy (like gravity) is a negative form of energy. You can see the link for more details ...

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Can matter be created in a pure vacuum (with no energy)? It's a subtle question. Firstly, how do we know whether there is energy? But even if there were energy if it was a minimum of energy then you wouldn't be able to use it to make things, and the energy minimum would be considered a good vacuum. But can you make particles? If they just appeared ...

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