# Questions tagged [energy]

Energy is the conserved quantity associated to time-translation invariance and represents the work a system is capable of doing. Use this tag for questions about energy, and consider adding [tag:energy-conservation] if it is specifically about its conservation.

3,982 questions
1k views

### How much energy is wasted by a noisy refrigerator?

I recently bought a new refrigerator for my kitchen. The feet are adjustable but I've been lazy. Whenever the motor runs and the feet aren't all touching the floor there is a loud buzzing noise. As ...
99 views

### Meaning of $E$ in time-independent Schrödinger's Equation (high school)

I've just learned the time-independent Schrödinger's equation as $$-\frac{\hbar^2}{2m}\cfrac{d^2\psi(x)}{dx^2}+V(x)\psi(x)=E\psi(x).$$ Does $E\psi(x)$ mean that $E$ is a constant (that the kinetic ...
37 views

### Potential energy of the oscillator

Is there a difference between the potential energy of an oscillator and the potential energy of the spring which is associated with? When we compress a spring horizontally without any object ...
75 views

### Finding an energy of a particle in an infinite potential well

This question arises from a discussion I recently had with my friend. We were talking about a particle in an infinite potential well. The particle is in an arbitrary wavefunction $\Psi$. When one ...
81 views

### Does a non-spherical black hole have distribution of mass like an empty body, solid body or pointed object?

Suppose a non-spherical (say, rotating or under distortion of another gravity source) black hole. Does it have its mass distributed as if all the mass was on its surface, or as if the mass were ...
27 views

### Which direction will this object move in at the end of this process?

1) Consider an object with no net force acting on it moving with a constant velocity v. It has a momentum mv. 2) Now let a force F1 act on the object. Let the direction of this force be opposite (to ...
29 views

### Gravity in classical energy

It's well understood that matter has mass, and more importantly gravity. I believe I am correct to say that gravity is more like an affect of matter. And not actually part of it. Ie mass bends space ...
38 views

### Energy of bound states in gauge theories

In gauge theories such as QED or QCD, are the rest energies, and therefore the invariant masses, of various bound states, such as those of positronium or charmonium, gauge-invariant observable ...
65 views

### In what context is enthalpy a convenient concept?

Internal energy $U$ is clearly an important concept; the first law of thermodynamics states that for an isolated system internal energy is constant $(\Delta U=0)$ and that for a closed system the ...
44 views

### Will Vacuum Energy persist at the Heat Death of the Universe?

By "vacuum energy" I mean the underlying background energy that exists in space throughout the entire Universe, codified in Heisenberg's energy–time uncertainty principle, a special case of zero-point ...
40 views

34 views

### Utility of work and energy

Why do we study the scalars such as work and energy if we know how to solve daily classical mechanics problem with standard mathematics? My second query is about the main motive of defining ...
151 views

### Newton's laws vs energy for solving a problem

I have a problem I solved using kinematics/Newton's 2nd law. It gives the mass of a walker as 55kg. It then says she starts from rest and walks 20m is 7s. It wants to know the horizontal force ...
79 views

### Is system boundary part of the system or the environment or neither?

The book says: As an example, imagine a force applied to an object in empty space. We can define the object as the system and its surface as the system boundary. Okay, if the surface of that ...
66 views

118 views

### Is it possible to create a limitless power by firing rocks from the moon to Earth? [closed]

Here is my idea for a limitless* power. A gun on the moon fires moon rocks towards the Earth. The moon rocks fall in Earths gravity picking up speed and smash into Earth's atmosphere generating huge ...
71 views

### Do empty orbitals have energy?

Suppose we have the Na (Sodium) atom. It has half-filled the 3s orbital and unfilled 3p orbital. Does the empty 3p orbital have energy? also does the energy of 3p change if an electron occupy it?
52 views

### Using coil gun make two mass of lithium deuteride collide and start nuclear fusion

We already have hydrogen bomb, why controllable nuclear fusion so difficult? And why controllable necessary? If we can detonate a tiny hydrogen bomb， we can collect the energy, like laser nuclear ...
18 views

### volume of liquid in a boiler based heating system

We're trying to improve energy efficiency for my dad's hothouse. The setup includes a gas boiler and a pump running the heated water thru special pipes to heat the grow space. My question is, leaving ...