# Tag Info

0

I have had an idea but I do not know whether or not my analysis is flawed. Rather than starting by looking at a motor I want to start with a consideration of a generator. A conducting coil $WXYZ$ with a small gap in it is in the plane of the screen rotating as shown in the diagram with side $XY$ coming out of the screen and side $WZ$ going into the ...

1

Definitions First, let's start by defining some parameters: $\mu_{o}$ is the permeability of free space $\varepsilon_{o}$ is the permittivity of free space $\mathbf{E}$ is the 3-vector electric field $\mathbf{B}$ is the 3-vector magnetic field $\mathbf{S}$ is the 3-vector Poynting flux (also called the Poynting vector) $\mathbf{j}$ is the 3-vector ...

0

It didn't go into anything. Energy is not conserved "globally," it is conserved in "local" Lorentz frames. If you like the idea of the continuum, you might say that energy is conserved "precisely at each point in space," but only approximately as you increase the size of the region. Of course our models of physics in local Minkowski frames assume ...

2

Well, if you want an answer at the 9-grader level, it's probably this: We don't know, and it's mostly irrelevant to how the universe behaves now. In particular, the Big Bang Theory doesn't care about what happened before the Big Bang. According to many interpretations of different branches of physics, the question doesn't even make sense, e.g. what happened ...

2

The simplest way to look at this is that energy can also reveal itself in negative forms. Don't think of it as something only positive, but also there's a negative part of it in the universe that's not directly visible. For example, we have good reasons to believe that the total energy in the universe adds up to zero. We also have experiments that show ...

0

Heat energy and thermal energy are pretty much the same thing. My science teacher taught me, that because potential energy is related to height, it would be the kinetic energy that is converted into th

1

It is a method that is generally used for conservative unidimensional problems (problems with only one degree of freedom, here your angle $\theta$ or cartesian coordinate $x$). You'll notice that it is equivalent to using Newton's second law in this case : let us write the total energy $E = \frac{1}{2} m v^2 + V(x)$, $V$ being potential energy. The problem ...

0

Magnetic fields is created by the low atomic magnets inside the piece of metal, piece of iron aligning together in a line. The actual magnetism in a piece of iron or in a permanent magnet is actually caused essentially by electrons orbiting in one direction more than the other, and the electrons are going to keep on orbiting forever until something ...

0

If A would gain kinetic energy, it would move far from B. As A would move more far, Potential Energy of B won't increase as distance had increased proportionally.

1

There is no conflict here. Let the two charged particles ($M,Q$) be the system with no external forces acting. Momentum is conserved and so for all time $M_BV = M_A V_{Af} + M_BV_{Bf}$ Energy is also conserved and so for all time $\frac 12 M_B v_B^2 + \dfrac{kQ^2}{R_i} = \frac 12 M_B v_{Bf}^2 + \frac 12 M_A v_{Af}^2 + \dfrac{kQ^2}{R_f}$ The ...

6

Potential and potential energy are defined for pairs of objects, not individual objects. It's meaningless to say "the potential energy of A". One must say "the potential energy of the system consisting of A and B". There is only one potential and potential energy in your problem. Perhaps the confusion comes from the way potential is introduced in ...

0

You know that the centripetal force is given by $\vec F_z = m\omega^2r \, \vec e_r$ ,where $\vec e_r = \cos \theta \, \vec e_x + \sin \theta \, \vec e_y$ is the unit vector in radial direction. We want to calculate the work given by the line integral $$\int_C \vec F_z \cdot \mathrm d \vec r$$ where the position of the point mass $\vec r = r\, \vec e_r$ ...

1

I came up with a solution seeing John Rennie's comment. The centripetal force, $\vec F= -F \hat r$ so infinitesimal work done by centripetal force, $$dW=\vec F.d \vec r= -F \hat r.d\vec r$$ but, $\hat r⊥d \vec r$ so $$dW=0$$ is this correct ?

0

This is very similar to how plants capture CO2 and form "fuels" (sugars) to feed themselves. In the natural case, the energy comes from sunlight captured by the chlorophylls in the plant cells, and the chemical reaction is carried out by a group of enzymes (Photosystem I and Photosystem II). A lot of scientists are trying to replicate this process ...

0

Generators often have two sets of windings - one arranged on the stator (fixed) and the other on the rotor (spinning). One is chosen/designed to be the excitor (could be either the rotor or the stator); the excitor is fed a small amount of electrical power to maintain a magnetic field. The other winding generates the output as it moves through the field ...

2

Momentum, energy, angular momentum, and charge are conserved locally, globally, and universally. One must remember that conservation locally (within a defined system) does not mean constancy. Constancy occurs only when the system is closed/isolated from the rest of the universe. Conservation means that these quantities cannot spontaneously change. Let's ...

2

In a collision momentum is conserved if there are no external forces. enefgy is also cionserved but in the examples kinetic energy is an important parameter. Elastic collisions are ones when kinetic energy is conserved. In non-elastic or inelastic collisions kinetic energy is not conserved and some kinetic energy can be converted into heat, sound and in ...

0

"velocity would stay constant, mass would decrease and so the momentum of the trolley decreases" , is a correct argument , but if this is a system where gravitational forces are present , you have neglected the pressure on water flowing through the hole in the trolley .The pressure on water flowing through the hole will produce a velocity(1) in it ...

1

This equation holds whenever there is constant acceleration. Here are 2 ways of deriving that equation, which I hope help you understand it. Energy conservation The change in kinetic energy must be equal to the work done on the particle. $$\frac{1}{2}m v_A^2 - \frac{1}{2}mv_B^2 = \int F\cdot dx$$ For a constant force and mass $\int F\cdot dx = F (x_A - ... 0 Pseudoforce are real forces, i.e., they do everything a normal force would do. The problem with conservative nature is that if the observer is moving in a bizzare fashion so that somehow the curl of its acceleration becomes non zero, then the pseudoforce will be non conservative. For observer moving in one direction, force will be conservative and if you ... 0 It is possible for a capacitor to have a net charge. However, most components have a small capacitance with respect to infinity. Unless you're dealing with a huge metal ball, it will take a large voltage in order to get any appreciable charge there. 0 Perhaps a better way to put this question is how is energy concentrated within a resonant system? As others have already stated energy is always conserved if one considers the universe in tallying where energy comes and goes. But if you are considering a system, defined within spatial boundaries, the system can lose or gain energy through its boundaries. In ... 3 The answer you cite is somewhat simplified to suit the level of the question. The vacuum does not consist of pairs of particles and anti-particles popping into existence and then disappearing again. When calculating the properties of the vacuum it's true that we use Feynman diagrams showing the creation of particle/antiparticle pairs, but these are virtual ... 1 Lift is approximately proportional to velocity squared of the aircraft, not the thrust. That is why runways are required. So the thrust is used the accelerate the aircraft to take-off velocity, which will produce enough lift to overcome gravity. Also, the fact that the thrust is less than the gravity in Antonov implies that it can't do this: ... 1 Just think about how you might push a child's swing. You apply a push once every oscillation of the swing and thus build up the amplitude of the swing. This is a resonance condition whereas if you pushes the swing at a slightly lower frequency you would not be able to increase the amplitude of the swing as much. Once the swing is at a constant amplitude ... 0 I also had hard time to picture what Feynman wanted to explain. It feels like my confusion arose from lack of proper definitions of system state, perpetual motion, and reversible machine. The examples he used are also not quite clear of the mechanical apparatus used, not sure if by design he wanted to abstract away that from the reader, but if so, I would ... -1 Lets say you take the theoretical function multiverse and use eulrtivic manifold distribution of stellar parallax (EMDSP equations) to find the conserved mass/energy of the two variables (energy, mass/consequence of gravitational flux) then one should find a percentage of mass being quite content and conserved. 0 The majority of the energy is dissipated as mechanical deformation (as Jon Custer has stated). Visualizing the situation can help a lot. All matter is somewhat elastic - there's no such thing as infinite elasticity. When an object collides with something, the force of the collision takes time to spread out across the object. Imagine a slow-motion view of ... 0 The energy has several options to get dissipated into: Major part of it is turned into heat as a result of friction. Some part gets transmitted into sound energy, causing the sound we hear when the object falls. A very feeble amount gets transformed into light energy. Another miniscule portion is utilised in deforming the object and thereby increasing the ... 0 But cooling does release heat. If you heat a chunk of iron to 200 Fahrenheit and place it in a closed insulated room as the iron cools it will heat the room. You could say something contains a certain amount of heat as in the heat required to take it from absolute zero to its current state (including temperature). But that does not mean much as the ... 2 All friction can be ignored. In that case Conservation of Energy applies: $$U+K=mgh$$ So that when the mass reaches the bottom of the ramp: $$K=\frac{mv^2}{2}=mgh$$ My question is: The mechanical energy of which system is conserved in the progress? The one formed by m and M, or the one formed by m, M and the Earth? The system here is mass, ... 0 The values presented in the bar chart aren't really energies, they are changes in energy. Using the frame of reference shown ($y$-axis) the kinetic ($K$) and potential ($U$) energies at point 1 are: $$K_1=0$$ $$U_1=mgy$$ Assuming no friction or air-drag acts on the car, then Conservation of Energy applies, so: $$K+U=\text{constant}=mgy$$ When the car ... 1 Let's make things a little more fun. How can we use the conservation of energy equation to derive Schrödinger equation in QM? Let's say we know the system's Hilbert space$\mathcal H$and we know how to define a Hamiltonian$H:\mathcal H \rightarrow \mathcal H$whose average value$\langle \psi | H | \psi\rangle$provides the average energy in state ... 3 The Schrödinger equation cannot be derived from classical physics. There are various consistency checks and motivations, such as its consistency with conservation of energy, but it is not derived from those considerations. However, that the Schrödinger equation conserves energy is built in when one knows that the Hamiltonian is the energy operator since $$... 2 Quantum mechanics is not derived from classical mechanics or energy conservation, but there are "jumping off points" in classical mechanics that may serve to answer your question. If you study classical mechanics at a sufficiently advanced level you will discover the Hamiltonian formalism. The Hamiltonian for an isolated system with only conservative ... 2 When studying physics, it is often necessary to make simplifying assumptions in order to keep the math manageable. In the case of an elastic collision between two balls, the textbook example ends with the kinetic energy of the two balls being conserved through the collision. As you've noted, this ignores the energy lost to sound - it also ignores the ... 0 No collision is perfectly elastic. Everything loses energy in the form of heat. Some processes (like aspects of photosynthesis and LEDs producing light) are nearly 100% but never exactly 100%. In quantum mechanics, there are reversible events (which may be the same as being in superposition) that are 100% efficient. As soon as the probability of reversal ... 2 Considering the way how v^2=v_0 ^2-2g\Delta y is derived, It is derived through energy conservation, that is$$\frac{1}{2}mv^2-\frac{GMm}{r+\Delta y}=\frac{1}{2}mv_0^2-\frac{GMm}{r} \tag{1}v^2=v_0^2-2\frac{GM}{r}\bigg(1-\frac{1}{1+\frac{\Delta y}{r}}\bigg)$$Using Taylors series$$v^2=v_0^2-2GM\bigg(\frac{\Delta y}{r^2}-\frac{\Delta ... 2 Your first part was correct; but for the second part, you have to equate the energy of A plus the stored energy in the spring to the energy of B (because you start with no energy in the spring, and all the energy as kinetic energy in B). So the expression for the stored energy is$E_\mathrm{spring}=\frac12 k x^2 = \frac12 m_b v_b^2 - \frac12 m_a v_a^2$. ... 2 In a static spacetime, there is (by definition) a timelike Killing vector field$\xi^\mu$, which implies that geodesics with four-velocity$u^\nu$have a conserved quantity$\epsilon = -g_{\mu\nu}\xi^\mu u^\nu\$. For example, in Schwarzschild spacetime, this is $$\epsilon = \left(1-\frac{2M}{r}\right)\frac{\mathrm{d}t}{\mathrm{d}\lambda}\text{,}$$ where ...

0

I send a blue photon up to my friend, who is x meters above me in some tower (we are both at rest relative to each other). He measures the photon and finds out it is red. We both conclude that a gravitational redshift occurred. However, where did the energy go? It didn't go anywhere. The ascending photon didn't lose any energy. There is no magical ...

Top 50 recent answers are included