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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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Below (in the picture) is my attempt to work the Atwood's machine via conservation of energy.

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In an inelastic collision, some of the energy is absorbed by the colliding bodies - this is why you cannot use conservation of energy to calculate the resultant velocities of the bodies involved - you don't know how much is absorbed. But you do know that momentum is conserved, and assuming that the bodies remain intact (no pieces are separated from the ...

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Expanding on what Sofia said, the mass above the Earth isn't an isolated system because gravity is acting on it. As she said only approximated isolated systems exit, imagine a lump of iron in a room. There is a magnetic field set up in the room, but because you are inside it you don't know it. The lump begins to move and you measure KE. You would conclude ...

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Suppose someone suggests that following a perfectly elastic collision, two billiard balls are each traveling twice as fast as they were before (and opposite to their original directions). You can't prove him wrong using conservation of momentum, but you can prove him wrong using conservation of energy. Therefore conservation of energy has implications that ...

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Your $E$ is potential energy in the rubber, which transforms to kinetic $K$. So your starting velocity $v$ will be: $E=1/2 mv^2$ From conservation of energy: $0-1/2 mv^2=0-mgh$ $h=v^2/2g$ and $v^2=2E/m$ Confirmed Interestingly enough the rubber does not obey Hook's law, and you need a lot more work if you want to find out what really ...

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A better question in this case is to ask if we drop a feather from a height, we see that the feather settles on the ground quietly. I you can under this which is a lot easier to explain and much mor intuitive. So as any object falls in a fluid (in this case air) it firstly accelerates and finally reaches constant velocity termed as terminal velocity, at ...

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Just before the ball reaches the ground, all of its molecules are coming down with almost an equal speed that is the speed of the ball.(Although, due to the non-zero temperature of the ball, the molecules are also vibrating about their mean position wrt COM frame of the ball).And thus the ball possesses a systematic macroscopic kinetic energy. Now when ...

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If you're dropping a projectile into sand, the potential energy that you began with ends up being converted into kinetic energy (from the sand thrown out from the collision), sound energy, and thermal energy. Ultimately, the thermal energy is the only surviving energy after any appreciable time though.

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Typically, the Friction force will be proportional to the velocity of the object it affects (or at least it is usually assumed to be proportional). The Force you describe is constant and pointing in negative x-direction. The situation you are describing resembles an object on a Hookean spring in a gravity field. At first, F1 pulls it upward (positive x) far ...

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Based on work that I've done in the past, automobiles moving at "normal" highway speeds of 50-60 mph experience total friction forces of approximately 50% wind drag and 50% rolling resistance. Two identical and separate cars driving at 50 mph could reasonably be expected to get the same gas mileage. If one of those cars was tied to the rear bumper of the ...

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The math is almost trivial for someone beyond algebra 1. Write the kinetic energy of each particle as $p_n^2/2m_n$. Then converse momentum and kinetic energy in the center-of-momentum. You will see that the magnitude of the momentum each particle does not change.

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It is not that easy. Now one engine is delivering about twice as much torque and was probably not designed for that. An engine specifically designed to deliver more torque would like be more efficient than the two combined. Lets look torque alone. Ignore the tow rope and assume the second is far enough back to not get any draft. In this case wind ...

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You can read the abstract of the Tajmar paper here: http://arc.aiaa.org/doi/abs/10.2514/6.2015-4083. Important quote: We identified the magnetic interaction of the power feeding lines going to and from the liquid metal contacts as the most important possible side-effect that is not fully characterized yet. Our test campaign can not confirm or refute the ...

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Assuming that the angle theta is measured relative to the vertical (e.g., the position of the string when the pendulum is at rest), a careful free body analysis indicates that the acceleration of the pendulum is g * sin(theta). This means that the acceleration of the pendulum continuously varies as it swings. This is relevant because the kinematic ...

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Heat and sound, which then also is converted into heat. The total energy of the system is thus conserved.

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The energy gets converted into the form of heat and sound. In this way the energy is conserved.

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The solution has to have with the 'surface tension' of the exterior surface. Google for 'surface tension' satin water repellent synthetic tissue and find: 'Liquid water is prevented by surface tension from penetrating' on Polyester Microfilament Woven Fabrics Conclusion : the exterior surface of the duvet (and not the interior material) is blocking the ...

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Energy kinematics I have this question, because typically problems that can be solve using conservation of energy or just energy-related principles, can usually be solved sing kinematic equations. Yep. In fact, there are two profound pieces of math, Hamiltonian and Lagrangian dynamics, which say that you can use energies to derive the actual kinematic ...

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As noted in the comments, weight must be evenly distributed or the washing machine will spin off center and shut down. Clothes are a lot of small pieces. When spinning starts, they fly to the outside. Usually they are uniformly distributed. A duvet is a single large piece. It is easy for it to be off center. For example, if you wrap it around the ...

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Fans make air molecules move, and the energy is in a such case converted to kinetic energy. TV:s, and everything else with screens, are also giving off photons, which carries energy. All electronics also produce heat, which is a form of energy. In the end almost all energy is in some way or an other converted into heat, due to Thermodynamics – or more ...

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When thinking about converting into another form, it does not have to be usable energy again for example when fan spins it makes sound due to it hitting other air molecules and thus giving them energy and so causes noise and heats up air every so slightly(after all noise is air vibrating). Next, the energy is converted into heat due to the friction between ...

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The fan increases the kinetic energy of the air molecules in the room. From there the energy usually dissipates uselessly (molecules bouncing off of each other, different objects, and you) but if you tried holding up a pinwheel, it would rotate proving that the energy has just been converted to a new type. The net result of the fan is a rise in temperature, ...

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A simple solution can be like this- At first you find the rate of change of Kinetic Energy. The process is as follows. $$d/dt(1/2 mv^2)$$ =$$F.v$$ Now imagine this case of a constant force acts on the body which equals to -mg(minus indicates downward direction). So, the equation is -mgv.Now the velocity is the rate of change of vertical position of the ...

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We may construct a system with Hamiltonian not $T+V$ but energy still conserved from any system where energy is conserved by making the phase space description generally covaraint: Starting from an unconstrained Hamiltonian $H_0(p,q)$ with Hamiltonian action $$S_0 = \int \left(p_i \frac{q^i}{\mathrm{d}t} - H_0(p,q)\right)\mathrm{d}t$$ we may turn it into a ...

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These to me sound like they're two sides of the same coin. If you lose locality of interaction, then you lose locality of energy conservation, and you therefore have, among other things, combinations of energy transfer which simply push the energy out to $\infty$ instantaneously, creating a pathological global violation. I am not sure that I buy your ...

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It's just a way of saying that the S-matrix only connects initial states to final states that have the same energy and momentum. With finitely many states the S-matrix is a finite matrix, and the $m$:th element in the $n$:th row is non-zero if the time evolution of the $n$:th initial state has an $m$:th state component. In an energy conserving theory, it is ...

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You're right that the kinetic energy of the spacecraft is the same both before and after the planetary encounter—in the reference frame of the planet (or, technically, the frame of the planet-spacecraft CM.) But the fact that the kinetic energy is the same before & after in one frame does not mean that the kinetic energy will be the same before & ...

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Feynman's trajectory The trajectory discussed by Feynman is shown below in red for the blue path, which is a hyperbolic deflection of a small particle around a large star centered at $(0, 0)$. Discussion Feynman's trajectory here trying to answer the question: how much has the speed increased between A and B. He is answering that by saying that there is ...

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One should always remember that quantum mechanics predicts probabilities and not energy distributions . The energy a particle will have is an eigenvalue of the energy operator operating on the wavefunction, but the probability of finding a particle at (x,y,z) at time t is given by the complex conjugate square of the wavefunction which is the solution of the ...

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As mentioned in the link you provided, it is due to Heisenberg's uncertainty relation $-$ during the short-lasting tunneling, the particle may temporarily borrow some energy from the potential of the barrier, so sometimes it can jump over it. Well, the energy and time may be depicted as a sort of Fourier transform pair (see Fourier transform) because the ...

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The particle doesn't borrow energy. Your idea that it gains energy is a guess about what is happening during the experiment, and it is wrong. You are thinking of a particle in a tunnelling experiment as being like a ball rolling up a hill that is too high for the ball to get over the top with the amount of energy you have given it. The ball rolls part way ...

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On a quantum level, particles don't really have "momentum". They're waves. The way the Schrodinger equation works, they move faster if they have a shorter wavelength. So we defined momentum based on the wavelength. Kinetic energy also is part of the whole conservation of energy thing, so we have a very good reason to define it how we did, but again, it's ...

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You mean quantum tunneling? The particle doesn't really "borrow" energy, actually a particle will have a higher probability of tunneling through a barrier if it has a high kinetic energy. A naive analogy would be that the more energetic the bullet is, the higher the probability it has of piercing through a wall, that is, tunneling. What makes quantum ...

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Here is what I think he means: first we have a planet going around the sun in some orbit, then we change the direction of the velocity to go radially outwards, for example by letting the planet go inside some pipe we put in it's path (notice that a normal planet would never do this, because there are no big pipes in space and also there would be quite a lot ...

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SECTION A : The example in Feynman's Lectures Let a body P (Planet or Particle or whatever) moving in orbit around a center of attraction called $\:\rm{SUN}$, as in above Figure. Suppose that the attractive force $\:\mathbf{f}\left(r\right)\:$ depends continuously only on the distance $\:r\:$ of the body P from the center $\:\rm{SUN}$. Here it's not ...

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The point is that if $\frac{1}{2} mv^2 - GMm/r$ is constant, then $v$ only depends on $r$! This is surprising and very useful; it means that $v$ will be the same no matter what path a planet takes from some $r_1$ to $r_2$. In this case, the two paths he's using are the planet's usual elliptical orbit, and a path that goes straight toward the sun. You don't ...

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You seem to be asking two questions: why is the current on either side the same, and what happens to the energy. To clarify where the energy goes, the kinetic energy is transferred entirely into electrical potential energy of the capacitor. This is the energy stored as a result of all the similar charges being close together on either capacitor plate. There ...

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I think the first law of thermodynamics could be restated as $$\Delta U_S + \Delta U_{\Omega\setminus S} = 0$$ i.e. $$U_S+U_{\Omega\setminus S}=\text{constant}$$ and this would clarify (to me) the relationship between the two concepts. What you describe is a general law of conservation of ...

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The experiment you link is Joule's classic paddle-wheel experiment. Specifically, Joule determined that applying 772.24 foot pound force via the weight produced a rise of 1 degree F in one pound of water, although later, more precise experiments gave slightly higher numbers. The experiment is described in exhaustive detail in Joule's paper, a copy of ...

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The experiment was designed to show that a mechanical process (a paddle wheel stirring water) could cause the water temperature to rise by a predictable amount. The equivalence was tested by using a system in which the mechanical work could be easily measured, a mass falling in a gravitational field. It turns out that there are several linear relationships ...

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When a rocket is fired from Earth with a sudden impulse, its total energy is given by: $$E_k \text{ (kinetic energy)} + E_p \text{ (potential energy)}= \frac{1}{2}mv^2 - \frac{GMm}{r} = constant$$ The potential energy here is taken to be negative because the reference point chosen for potential energy to be zero is when the rocket is unbound in Earth's ...

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The easiest way to calculate escape velocity, is neglicting Earths rotation and assuming the object takes of in a radial direction. Then, indeed, you start from $$E = K_1 + U_1 = K_2 + U_2$$ where $K_1=\frac{mv^2}{2}$ and $U_1=- \frac{GMm}{r}$. Since the range of gravitional forces is infinity, you say (theoretically, not practically) that an object has ...

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