New answers tagged

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Yes, there are lots of potential energies, one for each different force you can imagine. Magnetic force is a good example, if you hold two magnets apart from each other with the north pole of one magnet directed toward the south pole of the other magnet, they will feel an attractive force (but it is not an inverse-square law force like gravity). You can ...


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What you have here could be described as a subset sum problem. Given $n$ can take any integer value (not including zero), you have the set of squares up to $36$, $S = \{1,4,9,16,25,36\}$ and you wish to find subsets of three which sum to $41$. Looking at the subset sum problem this can not be solved analytically but algorithms can be employed. To do this ...


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In special relativity the transition from one frame to another is given by the Lorentz boosts. This is not quite the same as an acceleration, but a transformation that relates observations on one frame with another. We can think of an acceleration as being a succession of infinitesimal Lorentz boosts that map one frame to another. The infinitesimal distance ...


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All three are "correct", and all three refer to mass-energy equivalence discovered by Einstein. Equations (2) and (3) are algebraically identical, and are generalizations of (1). Equation (1) only takes into account an object's rest mass, whereas equation (2) also takes into account the momentum $p$ of the object, and (3) takes into account velocity $v$. ...


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The photons released are individually massless, but all of them together have an effective mass equal to the original masses of the particle and antiparticle; see my answer here. This isn't some mathematical abstraction either -- you can put the photons in a reflective box and weigh it, and it'll have extra weight. It's safe to say that the phrase ...


4

Notice that in the finite approximation the vector PR is not perpendicular to the radius, so work is done on it. By the drawing, this work is of the opposite sign that that in QR, so they both compensate to zero. I'll leave to you to compute both if you are really interested. Another way to see it, the gravity force is derived from a conservative field, so ...


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Work done by a central force is Zero. At every moment the force is perpendicular to the displacement of the test particle. If you see your diagram it's very easy to see that at the final and initial position of the particle the force is not in the same direction. What he actually does is to assume that P and Q are actually arbitrarily close. So now the ...


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There are already good answers here, but I'm afraid that to the best of my knowledge, Diracology's (and indeed Halliday-Resnik-Krane's) expression of the potential energy is not correct. I would like to point to this paper by Lior M. Burko which focusses on the subtleties of the derivation of the kinetic and potential energy of the string as a whole and ...


1

But the acceleration is not a partial derivative! Its a total derivative, $\frac{\mathrm dp}{\mathrm dt}$, with a $\mathrm d$ instead of a $\partial$. Anyway, I guess you might want to read about the Hamilton-Jacobi equation.


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Almost everything from the wikipedia page you link is just false, or at best very misleading. IMHO, that page was written by someone that doesn't know anything about quantum mechanics beyond what one could find in TV documentaries. "Not even wrong" came into my mind many times as I was reading the article. In quantum physics, a quantum fluctuation (or ...


1

This is an every day term, with no meaning for physics. In the Oxford dictionary for "energy" one gets: Physics The property of matter and radiation which is manifest as a capacity to perform work (such as causing motion or the interaction of molecules) In science fiction one might separate zero mass particles, like the photon and the graviton ( ...


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The work done onto the spring is $dE/dt=F(t) \dot x(t)$. You should not look at the direction of $F$ alone, but at the the direction of the motion as well.


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Let say the power produced by a transmission company is 50 Giga_Watt(we can take any value really). What happens is, they convert this to very high voltage.When you use a 1 kilo_ohm resistor, the current draw should be 22 amps, but the power generated(50Kw) must be kept in mind! You cannot have a power source of 10 W and expect it to provide 10 Volts at 2 ...


1

Your question seems to be about heat transfer through convection. The formula that describes this phenomenon is: $dQ/dt=h*A*(To-Tenv)$ where $dQ/dt$ is the heat transferred per unit time, $A$ is the area of the object, $h$ is the heat transfer coefficient, $Ta$ is the object's surface temperature and $Tenv$ is the fluid temperature (temperature of air ...


2

Your scenario is actually a classic transient conduction problem tackled in undergraduate engineering heat transfer, so we can handle this scenario easily. I took the figure below and adapted a derivation from a popular heat transfer textbook by Incropera and DeWitt: In this figure a warm object is placed in a tank filled with a known liquid (the ...


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The second derivation is correct, as explained by Diracology. However, the first derivation is 'sort of' correct, in the sense that the location of potential energy can be ambiguous. For example, consider the three following systems. A mass on a stretched spring. A mass sitting on a table. A charged mass next to another charge. These three systems have ...


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The energy of an element of a traveling wave is not constant. Halliday-Resnick-Krane is right. For a string of density $\mu$ and tension $T$ the kinetic energy of an element $dx$ is $$dK=\frac 12\mu dx\left(\frac{\partial \xi}{\partial t}\right)^2.$$ For the potential energy we have $$dU=Tdl,$$ where $dl$ is the stretched amount of the string. A small ...


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If before putting the mass $m$ on the piston, in absence of external constraints, the piston is in equilibrium; since it is not mentioned in the problem description that gas has received some amount of heat; thus it is impossible that the piston moves upwards after putting the mass $m$ on it due to gas pressure. So, this question violates physics laws and we ...


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Work, by its definition, is by mechanical. Potential energy and kinetic energy can be converted from work. We also talk, for example, heat using energy, which seems has nothing to do with either potential energy or kinetic energy. But later, you will find in statistic mechanics, heat is related to the kinetic energy of particles. But it is too expensive to ...


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In a simple DC circuits the charge carriers will drift through the bulk volume of the wire and resistor. Collisions in the resistor (and also wires) will be converted in heat and effectively transferring battery energy to the resistor and less so to the wire. There will be net charge accumulation on the surface of the wire and resistor maintaining the ...


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As knzhou mentioned, this is true even for progressive waves in a string. Your mistake might be to think about simple harmonic motion instead of harmonic waves. I will show it for a progressive transverse wave in a string. It is easier to visualize. At the end I will give you a sketch for longitudinal waves. For a string of density $\mu$ and tension $T$ ...


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Yes Energy can be defined without reference to work. In the context of more advanced physics like Lagrangian mechanics, There's Noether's theorem; It states that for every symmetry that's present in our laws of physics, there exists a conserved quantity(does not change with time) that is associated with this symmetry. For example, if the laws of physics does ...


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Joule, in his famous experiments, demonstrated the one-to-one relationship between mechanical work and internal energy change. Later, others demonstrated the equivalence between these and electrical work (and other forms of energy).


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In kinematics one describes and analyzes trajectories, but not their connection to other physical processes. There is no force in kinematics. The concept of work uses the concept of force, so it does not belong to kinematics. It belongs to dynamics, a study of origins of changes in the motion. if it is then why is it used to define energy? can energy be ...


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Force The tendency to make something accelerate. Newton's 2nd law: $$\sum \vec F=m\vec a$$ Physical strength Can be different things. E.g. hardness $H$: a materials resistance against "bumbs" and indentations in the surface, yield stress $\sigma_y$: the stress a material can withstand before starting to deform ultimate tensile stress ...


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Well the difficulty is when the ball in contact with wall. Few things you can consider. elastic impact. In this case, you can treat the ball as an elastic spring. When it impacts the wall with a speed, the kinetic energy will be converted to the spring's potential energy. And then, after it reaches the maximum deformation, the ball will spring back into ...


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Force, energy, and work are all just different ways for us to describe motion. Energy (more specifically kinetic energy) is a measure of how fast an object's motion is. If an object has non-zero velocity, it has energy by definition. Force is a measure of how fast an object's rate of motion is changing. If an object's velocity changes, it's experiencing a ...


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Visual Solutions (Now Altair) makes VisSim Software. Here is a demo block diagram that they have used to simulate a bouncing ball: The $1/s$ blocks are integrator blocks from the VisSim library. The plot of the bouncing ball with these parameters is shown below. If you are interested in running this, the demo comes with the install and you can download ...


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We have to talk about Physical Strength last, for two reasons: (1) we have to clearly define the other physics terms first, and (2) Physical Strength gets us into biophysics so we'll have to talk about how muscles generate force, etc. "Force" is a push or a pull or a twist (if a twist, then it is also called "torque"). Force is what is required to ...


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I have been wandering that same question for 40 years...I have asked all kinds of doctors and researchers, only to see a glaze form over their eyes. The question, I think, is not whether it exists, but how do you measure it. The problem is figuring out the machine that can measure it. And then, where to measure, because I think there will be not only an ...


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Energy is proportional to amplitude squared. The energy in the wave is spread out over the surface of a sphere. The area of this surface increases as the wave propagates outwards from the source and is proportional to $r^2$. So the intensity of the wave (power/area) decreases in proportion to $1/r^2$.


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The PE of the particle is converted into the KE of the particle $\frac12mv^2$ plus the KE of the disc $\frac12I\omega^2$ which is also moving.


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The $\frac m 2 v^2$ term is the kinetic energy of the "small particle". The $\frac {I}{2}\omega^2$ is rotational kinetic energy of the disc of mass $M$. You are just counting the kinetic energy of each mass once.


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The energy conservation equation can be written as below. I guess Cengel was making comments on each items. $$\delta U = Q -W + m_1(h_1+\frac 12 v_1^2 + gz_1)-m_2(h_2+\frac 12 v_2^2 + gz_2)$$ For steady state, we know $\delta U =0$, $m_1=m_2$ So reading the book, we can translate that to, q=0: $Q=0$ w=0: $W=0$ pe=0: $m_1gz_1 \approx m_2gz_2$ ke=0: ...


0

By E=−Z^2RE/n2 where RE is the Rydberg energy As n increase, EPE becomes less -ve(i.e. more +ve) , indicating higher energy level< Or EPE = 1/4πε( Qproton Qe-) /r, As r increase, EPE becomes less -ve(i.e. more +ve) , indicating higher energy level< Thanks to everyone that helped !< I beg to differ on the above explanation provided by ...


1

By E=−Z^2RE/n2 where RE is the Rydberg energy As n increase, EPE becomes less -ve(i.e. more +ve) , indicating higher energy level Or EPE = 1/4πε( Qproton Qe-) /r, As r increase, EPE becomes less -ve(i.e. more +ve) , indicating higher energy level Thanks to everyone that helped !


5

The potential energy stored in a two like charge system will increase with decrease in distance between them. While for a two unlike charge system, the potential energy decreases with decrease in distance (means potential energy gets liberated if they come close), accounting for increase in attraction. In the equation, you provided, the potential energy ...


8

The energy in a level $n$ is given by $$E = - \frac{Z^2 R_E}{n^2} $$ where $R_E$ is the Rydberg energy ($R_E = 13.6\mathrm{eV}$). Therefore, greater $n$ means lower energy (in absolute value), i.e., the electron is less bounded.


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If you have studied the open system version of the first law, you are aware that, for this mathematical representation of the energy balance, work is divided into two parts: shaft work and work to push fluid into and out of the control volume. The work to push material into and out of the control volume is combined mathematically into the energy of the ...


2

Hyportnex is right: you can be sure that the energy of the ground state (i.e. the energy of the state with least energy) is $E=\hbar^2\frac{a-\sqrt{a^2+2\omega^2}}{2}$, by simply comparing the values that you got. Furthermore, if what you want now is to find out the representation of the ground state itself, you just solve the linear system \begin{equation} ...


0

If the propane in the tanks are under pressure,then on connecting them, both tanks will be full of propane as it is a gas. Had it been water, or in a liquid form, then both the tanks will have the same level no matter how you arrange them.


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My guess is that it would be impractical. Your reasoning is basically correct: a longer right arm will grant you a larger $\Delta h$, increasing the speed of the projectile. But there would be some issues: The structure would have to be higher, otherwise the weight would smash into the ground. Hence, it will be heavier and more difficult to carry. The ...


3

If I understand your notation right, then by $h_L$ you mean the height of the left weight? In that case your formula doesn't make sense: To account for energy conservation, you would have to take the heights before and afterwards of the right weight. Then you get \begin{align} m_R*g*h_{before} = m_R*g*h_{after} + \frac{1}{2} m_L * v^2 \end{align} You ...


1

This is one of those three part dynamics questions. For the first part you need to use energy conservation to work out the horizontal speed of the person just before hitting the pole. The second part is the application of the conservation of angular momentum about the pole's pivot point when the person grabs hole of the pole. Note that the collision between ...


4

Actually, as someone pointed out in the comments, potential/kinetic classification is the only meaningful classification in physics. Potential energy is the energy which comes from interaction, and kinetic energy is the energy which comes from motion. Maybe you stumbled upon terms like chemical energy, thermal energy and so on. But chemical energy is just ...


1

Entropy has various uses in Physics. It was first used as a state variable for thermodynamics, connected to energy and heat. Later, it was revealed that entropy is a measure of the disorder of a system. By extension, it is a measure of the observer's ignorance or lack of expectation about the precise, microscopic state of a system. This in turn is related to ...


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In relativity, gravity is the word we use to describe curved space. Don't think of curved space as simply 'no longer flat', also consider that it includes a gravitational gradient that will cause matter to move across that gradient. As an example, Earth bends the space around where you are right now, with a vertical gravitational gradient, causing you and ...


1

Why can't there be any continuous energy band in an atom? This is the basic reason quantum mechanics had to be invented. Once the existence of positive and negative charges was discovered, Maxwell's equations when solved for a planetary model of a central positive charge and an orbiting negative one, are completely unstable, in contrast to the ...


0

An electron in an atom is in a bound state. Since it is a bounded particle, can analyse the problem with particle in a one dimensional potential box. Consider a one-dimensional crystal lattice with lattice constant $L$. We assume that the particle is free to move within this distance and cannot go outside. So we have two potential barriers that tend to ...



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