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.

learn more… | top users | synonyms

0
votes
0answers
3 views

Capturing kinetic energy of air molecules

How small a hole we can make on a 1mm thick metal plate? Can we make a hole slightly bigger than the diameter of the air molecule? If possible, can we make a small one way 'turnstile' inside the hole ...
2
votes
2answers
357 views

Why does a wind turbine have only three blades? [duplicate]

Why not four or five or even more? Intuitively, the more leaves the more power. So, what is the reason?
1
vote
3answers
48 views

How does an inductor store magnetic energy?

I am trying to figure out what the potential energy of an inductor with a current really means. In a capacitor, the energy stored works like this: if you let the plates attract each other, before ...
0
votes
0answers
28 views

What is the kinetic energy of a proton as it is falling towards the core of the star?

Given: Star's mass = $1.99e10^{30}kg$ Type II supernova occurs (in a simple form: the outer layers of the star fall into the now inactive core at speeds of 126000km/s) $10^{44}$ joules of energy is ...
-1
votes
0answers
26 views

Can the Betz limit be overcome?

The Betz Limit states that the energy extracted from a turbine can be no more than $\frac{16}{27}^{th}$ of the energy present in the wind flowing through it. Extracting more energy would make make the ...
-2
votes
0answers
67 views

Understanding sine waveform [on hold]

I want to study the basics of propagating a periodic signal, i.e. sine waveform, which is a power signal. Let us consider an alternating current and write its expression as $$I(t) = I_m \sin(2\pi f ...
0
votes
1answer
25 views

Work done by friction on a body?

I know that when a body slides over a surface, the work done by friction is not stored as potential energy in the body. It is dissipated in the form of heat. But why is it not stored as potential ...
0
votes
0answers
39 views

Kinetic Energy and reference frame

Two space ships A and B moving through space in the same direction. Space ship A moves 2m/s faster than B, its weight is 1kg and it has a 2 Watt engine. It is accelerating with full power for one ...
0
votes
1answer
32 views

Energy and momentum of a relativistic electron

The question is to find the magnitude, $p$ of the electron's momentum in the unit of MeV/$c$, given that the kinetic energy of the electron is 2.53 MeV. The answer provided by the book says, ...
1
vote
1answer
33 views

Will my induction hob be powerful enough? [on hold]

I'm looking to buy an induction hob to heat some water and I would like to know if its going to be powerful enough. If so, can it be done in, say, 1 hour? Additionally, what power rating could I go ...
1
vote
1answer
32 views

Preventing Heat Escape

Is is possible to completely prevent heat from escaping from a closed container? Here is a diagram of vacuum flask, which tries to implement the design - Vacuum Flask prevents heat from escaping ...
0
votes
0answers
50 views

What fills the space between the galaxies, stars and planets? [duplicate]

What fills the space between the galaxies, stars and planets with the exception of gas clouds, dust, atoms, elementary particles and electromagnetic radiation? What the authoritative opinions exist on ...
0
votes
4answers
103 views

Can a photon have little to no energy and/or speed?

Can a photon move more slowly than the speed of light and behave 'non-relativistically,' so to speak. Perhaps another way to express my thought is: could we stop a photon from moving?
-3
votes
3answers
74 views

Derivative of kinetic energy [closed]

I read that the derivative of kinetic energy=$F\cdot v$. I tried to differentiate (1/2) mv^2 with respect to time but each time I am getting $m*v$ and not $m*a*v$ which solves to $F*v$. My efforts are ...
0
votes
0answers
39 views

What time of day to run the air conditioner? [closed]

I live in the Rocky Mountain West, where the summer temperature fluctuation from low to high is typically 30-40 degree F. We have a seldom used house on the market. We would like the temperature to ...
-1
votes
1answer
34 views

Why is work done $F$ applied over a distance energy? [closed]

Why is $E=(1/2)mv^2$ named energy? It doesn't seem intuitive to me to call it such.
1
vote
2answers
25 views

Relationship between Fermi Energy and Average Energy

Electrons are in a one dimensional box of length 2L. What is the relationship between Ef, the fermi energy and E, the average energy? The answer is Ef/3 I looked up the formula for the relationship: ...
1
vote
2answers
43 views

Is possible to synthesize diamond at relatively lower pressures (6 to 7 GPa vs 12 GPa)?

Pure binderless nanopolycrystalline diamond can be produced from graphite when the graphite is treated with more than 12 GPa pressure and at least 2100°C temperature . If we treated graphite or ...
0
votes
0answers
48 views

Equipartition theorem and virial theorem differences?

The classical virial theorem and the classical equipartition theorem are clearly related. A version of the virial theorem is, \begin{equation} \bigg\langle \sum ^{3N}_{i=1} x_i\frac{\partial ...
0
votes
3answers
78 views

If you double the mass of a moving object - is its kinetic energy quadrupled?

My colleagues and I were having a layman conversation about fuel consumption of boats vs planes etc. I was pointing out that according to the formula $$ E_k = \frac{1}{2}mv^2 $$ if you double the ...
2
votes
1answer
44 views

Cylinder inside a cylinder - moment of inertia

A homogeneous cylinder with radius a and mass m rolls in a hollow cylinder with radius R. Determine the kinetic energy of the cylinder as function of $\dot{\theta}$. I'm sorry for ...
0
votes
0answers
18 views

Cylinder rotating inside another cylinder. [duplicate]

A homogeneous cylinder with radius a and mass m rolls in a hollow cylinder with radius R. Determine the kinetic energy of the cylinder as function of $\dot{\theta}$. I'm sorry for ...
-1
votes
0answers
23 views

Cylinderception. Rotation [duplicate]

A homogeneous cylinder with radius a and mass m rolls in a hollow cylinder with radius R. Determine the kinetic energy of the cylinder as function of $\dot{\theta}$. Alright, I found this ...
3
votes
1answer
101 views

Coin rolling, but not sliding. Kinetic energy

A homogeneous coin of mass M rolls, without sliding, along the x-axis with the axis of rotation being parallel to the z-axis. Let $\Theta$ be moment of inertia regarding that axis and $\vec{V}$ be ...
0
votes
1answer
45 views

Relationship between gravitational time dilation and energy?

The rate that a stationary clock slows down near a massive object, relative to one far away, can be read off from the Schwartzschild metric: ...
0
votes
2answers
62 views

Question about kinetic energy

I have a question about kinetic energy: Imagine two vehicles with velocities $v_1$ going at $30 \frac{\text{m}}{\text{s}}$ and $v_2$ at $50\frac{\text{m}}{\text{s}}$. If they hit each other, will ...
0
votes
1answer
23 views

Interaction Energy vs Force

I'm having a hard time determining the relationship/differences between interaction energy and forces. Say we have a system of two charged particles. Each particle will exert a force on each other ...
0
votes
0answers
28 views

Reactor for electrical energy design base assumption inefficient?

Im no physicist or engineer but as I observe our methods to obtain electrical energy I noticed a pattern where we cause a exothermic reaction, the resulting energy heats water, that turns into vapor, ...
0
votes
1answer
26 views

Plot of fusion energy output growth? [closed]

What would a chart of energy output of elements of mass X fused with hydrogen look like? What about X fused with X?
1
vote
0answers
38 views

question regarding work energy theorem [closed]

The question says A smooth track in the for of a quarter circle of radius 6 lies in the vertical plane. A ring of weight 4N moves from $P_1$ to $P_2$ under forces $F_1$,$F_2$ and $F_3$. $F_1$ is ...
0
votes
3answers
107 views

Is it possible for man to break Earth into 2 parts? [closed]

Many countries have extreme devastating nuclear weapons. Also they have weapons in very large numbers. I want to ask that Is it possible for man to break earth into 2 parts with the help ...
3
votes
1answer
148 views

Feynman Lectures: Why a non-reversible weight lifting machine cannot lift higher that a reversible one?

Consider weight-lifting machines—machines which have the property that they lift one weight by lowering another. Let us also make a hypothesis: that there is no such thing as perpetual motion ...
2
votes
1answer
41 views

Mathematical expression of energy storage

I don't know if anyone can help out there, but I guess it won't hurt to ask!! I'm trying to develop an idea which is as follows. Put simply, imagine a flat sheet of material which, when distorted ...
1
vote
1answer
51 views

Total energy of neutrons and protons

In a stable nucleus, are the total energies of neutrons and protons same?
0
votes
1answer
94 views

Why is wave energy zero at maximum deviation?

The equation for the energy density of a longitudinal wave in a thin rod is $$w = \rho\cdot \left(\frac{\partial \xi}{\partial t}\right)^2$$ So the energy density seems to be 0 when the deviation ...
0
votes
0answers
14 views

What is the equation to calculate the strength and radius of an electromagnetic pulse?

With this interesting answer on the blast force of a uniformly charged electron sphere, came another interesting question. What would be the strength and blast radius of an EMP launched from such a ...
1
vote
1answer
29 views

How much energy is saved when using luggage with wheels? [closed]

How much energy is saved when using luggage with wheels as opposed to carrying the luggage? Thanks.
0
votes
1answer
27 views

relation between potential energy, kinetic energy and sound energy of water

When water flows its PE gets converted into KE so what causes its KE to get converted into sound energy and what the difference will occur in its sound if it is provided with a parallel surface?
0
votes
2answers
29 views

Kinetic energy dissipation in braking a vehicle

Let's say a vehicle that weighs 20t is hauling along at 50m/s and we want to brake it down to a full stop. The kinetic energy we need to dissipate into heating up the brakes is ...
1
vote
1answer
30 views

Definition of internal energy

I have read some thermodynamical and statistical physics books but it feels like they always gloss over the definition of internal energy. In wikipedia they included terms like Kinetic energy. But ...
0
votes
2answers
44 views

Energy loss without work or heat?

Suppose we have a mass-spring system in equilibrium as in the above part of the picture(it's a frictionless surface). Then I attached a weightless rope to the mass from one end and a car from the ...
1
vote
2answers
33 views

Why the electric potential energy the charges carry in a electric circuit does not vary with its distance to the opposite terminal?

I understand that with wires assumed to be ideal, there is no resistance and subsequently no force acting on electrons, hence no work done and p.d. across any segment of wire. However, as the ...
2
votes
2answers
52 views

According to calculations why the current of a battery of a mobile is high?

If you pay attention to the features of your mobile's battery the voltage would be around 3-4V and power is 4-5 Wh (14400-18000 Ws) and with calculating the current you can find a very high ...
1
vote
1answer
41 views

Interpretation for negative energy of curves

Let $(M,g)$ be a Lorentz manifold and $\gamma :[a,b] \to M$ a differentiable curve. I understand we define the energy of $\gamma $ as: $$E[\gamma] = \frac{1}{2} \int_a^b ...
4
votes
2answers
113 views

Is the Einstein Energy-Momentum equation $E^2 = p^2c^2 + m_0^2c^4$ valid only for Free Particles?

Is the energy -momentum relation $$E^2 = p^2c^2 + m_0^2c^4$$ satisfied only by free particles or even bound particles? Does the Energy refer to total Energy(including potential) or only (kinetic ...
19
votes
3answers
5k views

What did Tesla mean by “there is no energy in matter”?

I was reading "THE ETERNAL SOURCE OF ENERGY OF THE UNIVERSE, ORIGIN AND INTENSITY OF COSMIC RAYS" by Nikola Tesla, and he states: "There is no energy in matter except that absorbed from the ...
-1
votes
2answers
70 views

If energy can't be created and can't destroyed [duplicate]

Then wouldn't be logical that all the energy in the big-bang-created-universe will equal to the energy that was released by the Big Bang? The sum is zero? Edit The cited dup is asking "Did the law ...
11
votes
3answers
2k views

When an atom is split, what form of energy is released?

When an atom is split, what form of energy is released? All of the websites I have looked at say there is a lot of energy released when an atom is split, but it never says what form of energy it is ...
1
vote
0answers
28 views

Internal heating effects of a circuit element?

The heat-up of a solid circuit component in an electric circuit (for which no chemical reactions, phase changes reactions or other stuctural changes take place) may include: Joule heating $\dot ...
0
votes
0answers
29 views

Determine the amount of energy used for baking a cake

Let's suppose we have a room of temperature $T_0$ with an oven of volume $V$, both filled with air of density $\rho$ and specific heat $c$. We need to bake a cake in the temperature $T_1$. Thus we ...