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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.

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A question on Work and energy in which a body is taken up a hill by a tangential force

The height of the hill is h and length of it's base is l.A force F which is always tangential is pulling the body up the hill. The friction coefficient between hill and body is $\mu$.The body is being ...
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2answers
54 views

Basics of energy

I am not able to understand the second paragraph well. Please elaborate me anybody
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34 views

Does the energy of the mass of the universe equal it's gravitational potential energy? [duplicate]

Does the positive energy equivalent of the mass of the universe derived from E= mc^2 equal the universe's negative gravitational potential energy, if Omega equals 1? It seems that converting matter ...
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6answers
103 views

If Work=0 for a force along a path, does that mean the force cannot move an object along that path?

Suppose we are given a 2D force vector field $F(x,y)$ (position dependent only, no time dependency) and we're given a path C in the plane, and we compute $\int_C F \cdot ds$ and get zero. I was told (...
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1answer
54 views

Does the First law of thermodynamics hold if the final state is NOT in equilibrium?

So we know the first low of thermodynamics holds for isolated systems $$\Delta E = W+Q\tag{1}$$ Now assuming we are in a thermally isolated system such that $(Q=0)$ we obtain $$\Delta E= W\tag{2}$$...
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Where does the universe gets its energy from? [duplicate]

Well let's just end everything like this. All the laws made are just theories. We don't even know how the 'big bang' happen. If space has a limited space but it keeps expanding what's outside the ...
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0answers
47 views

Is the work function a function? [closed]

The work function is the energy an electron needs to leave the metal. Why is it called a function? Its value is different for different metals, but that doesn't make it a function; density and melting ...
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23 views

Energy Density Calculation Formula?

What I wish to know is how does one calculate the energy density of materials such as silicon. I was told that a way of finding energy density is through the calculation of stress-Strain Curve. ...
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6answers
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How can an object with zero potential and kinetic energy ever move?

I am not sure how to ask this question but I am learning about potential energy in my high school physics class. From the definition of potential energy, (energy stored in an object with the potential ...
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2answers
76 views

Can magnitude be negative?

My teacher told that magnitude is the positive value of that quantity or the modulus of that quantity. he also told that vector quantities have both magnitude and direction and scalar quantities have ...
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0answers
14 views

impulse in inelastic collision in two dimensions

I'm trying to find the impulse in an inelastic collision of two particles.At the end of this page there is formula for that.But I cant reach it bu my own.Here is what I think is the way to find the ...
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0answers
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How is elastic hysteresis effected by time?

Here's how I understand the phenomenon: let's take the example of weights and rubber band, when a weight is put it does work on the band to stretch it, and heats it up, some of the heat gets ...
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1answer
25 views

How does one calculate the energy used depending on the velocity and air resistance of an object [closed]

I'm in need of a equation that can tell me how much energy/work I need to move an object inside a low air-pressure tube. The equation should (if possible) include drag, object velocity and mass. If ...
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2answers
64 views

Energy Expectation Value = 0 - Meaning?

I've solved an exercise of a given quantum system with 3 given states. We had to find the energy expectation value, when we put the system in the "second starting quantum state". So I did the ...
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1answer
28 views

Question about solution to Morin Leaky Bucket problem

In Morin’s Mechanics book, a problem called leaky bucket goes: 5.17. Leaky bucket ** At $t = 0$, a massless bucket contains a mass $M$ of sand. It is connected to a wall by a massless spring with ...
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4answers
90 views

How did we come up with the formula of the work done by a force? [duplicate]

I don't understand why the work represent the change in energy of a system. I understand the work energy theorem but where did we get the formula of the work from in the first place. Also when I ...
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1answer
25 views

Higher frequency waves

Can we artificially create extremely high frequency waves in the ( order of 10^60 )? how hard is it to create high frequency waves, and what limits are potential in doing so...
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2answers
44 views

Is (DC/battery) voltage a result of charge? or energy? or both?

Backstory: I’m a software engineer just getting into electronics and it seems that everything I’ve ever been told about electricity my whole life is a candy-coated lie. I can’t find consistent logical ...
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3answers
58 views

Lennard-Jones potential

For the Lennard-Jones interatomic potential, the portion of the graph between r = sigma and r = equilibrium has a negative potential energy (attraction) and a negative force (repulsion). I am trying ...
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0answers
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Relationship between work and kinetic energy?

Lab Question: What is the relationship between the work done on a car as it rolls down a ramp and its kinetic energy at the bottom of the ramp? We have a 30 gram car that starts above a table and ...
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2answers
51 views

how can internal energy do work?

how can internal energy do work? As far as i know, internal energy is the sum of KE and PE. But how can this, in turn, do work? It would be great if you can give me some scenarios. Thank you.
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1answer
17 views

Feeling sound; frequency and volume

How loud and "low" must a sound be in order for one to feel some physical sensation in response? I've read that below certain frequencies humans can be expected to "feel" sounds in their chests, and I ...
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1answer
38 views

How does thermal energy in a system do mechanical work? [closed]

Explain that a system with thermal energy has the capacity to do mechanical work. Also, in addition to this what are the differences between work and mechanical work?
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2answers
27 views

Relative energy [duplicate]

Suppose a ball is travelling at 5km/h, person A is travelling at 2km/h and person B is travelling at 5km/h in the opposite direction. The ball is travelling at 3km/h relative to A and at 10km/h ...
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1answer
12 views

Does superconducting magnet prevents energy loss when hadron is being accelerated?

I read up on how synchrotron works and electron will heats up by emitting photon when it is steering(accelerating) around a bend, so more bends more heat loss. By heat I mean energy not necessarily ...
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0answers
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Can the internal energy of an ideal gas ever be zero? Help me understand HW feedback

HW Q: Can the internal energy of an ideal gas ever be zero? Explain. My Response: (implied Yes) wrote ΔU=0 describes a system where *Case a: |Q|= |W|, Q= -W * means heat added to system is ...
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1answer
67 views

Explain how a golf ball and a football can have the same kinetic energy even if their masses are different [closed]

I know that this is possible, but I just don't know how to explain for a question on my assignment the formula for kinetic energy is $E_{k}=\frac{1}{2}mv^{2}$.
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4answers
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What does the 'cosmological constant' represent?

Newtons theory of gravity involves a gravitational constant $G$, however one does not refer to it directly, we speak instead of gravity or the force of gravity. Now Einsteins introduced a ...
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0answers
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Why are there no excitations by collision for the visible transitions in the Franck-Hertz experiment?

The minima of the I(V) graph for a Neon Franck-Hertz tube are approximately 20V apart from each other, this is usually explained by the fact that excitation by inelastic collision happens at about 20 ...
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2answers
81 views

Is there a connection between the energy distribution and time dilation?

Can anyone please help me understand what is descibed bellow? Scenario 1. We have a pair of atomic clocks. Let's call them clock A and clock B. We switch both of them on at the same time. Clock A ...
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1answer
35 views

Kinetic energy of disk rotating around axis parallel to the one through its center [duplicate]

Given the situation shown in the figure below. A thin disk with mass m and radius r is rigidly connected to one end of a massless rod with length l at its centre, with the other end of the rod ...
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4answers
46 views

Why does the GPE of an object always equal the work done?

I had a question that said, "If you do 100 J of work to lift an object over your head, what is the gravitational potential energy relative to its starting position? What would be its gravitational ...
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3answers
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Does potential energy get transferred from my body to a wall when I push a wall and fail to move it?

When I push a rock (and fail to move it), I do not do any work and therefore there should be no energy transfer. But my teacher says that, when one pushes a rock, energy is transferred to the rock ...
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3answers
167 views

What's the point of momentum? [closed]

I know this may sound like a strange question but I have always wondered what exactly the mathematical point of momentum is. I have understood energy to be an attempt to reformulate Newton's 2nd law ...
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1answer
30 views

Total energy, total momentum of two different balls [closed]

I have a ball out of plasticine thrown horizontally with speed $v$ on a steel ball that is attached from top to the ground on flexible straps in the middle (see picture). The mass of plasticine is $m$,...
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2answers
80 views

Electrons Getting mass from energy

According to relation $E=mc^2$ energy and mass are equivalent. So, when an electron in its orbit gets energy from out, does its mass increase? If not, where is the energy stored? I am not ...
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2answers
43 views

Calculating initial average energy of a thermal state

We are given a system with the Hamiltionian $$H = \sum_i \omega_i a^{\dagger}_ia_i \tag{1}$$ where $a^{\dagger}_i, a_i$ are creation and anihilation operators. I did the calculations and got the ...
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1answer
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Can fire create pressure if it released it energy as fast as an explosion [closed]

Since fire release energy, I wanna know if it can create a shockwave if it release it energy as fast as an explosion
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1answer
19 views

Energy recovery from refinery cooling tower

Is there any possibility of recovering exhaust energy from a cooling tower by putting a wind turbine above it? Would this affect the performance of the cooling tower?
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4answers
96 views

Why do we use heat engines if they are so inefficient?

Let's say I wish to build an engine which will launch a box vertically upwards. I propose two such engine designs: Engine 1 (finger, spring, box) Step 1: Orient uncompressed spring vertically. ...
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2answers
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Conceptual understanding of Schrödinger equation

So I followed this lecture: https://www.youtube.com/watch?v=qu-jyrwW6hw which starts of with the statement: If you have a Schrödinger equation for an energy eigenstate you have $$-\frac{\hbar}{2m}...
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0answers
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Magnitude of mass polarization

When solving many-body atomic Hamiltonians, (such as Helium), there exists a term in the Hamiltonian which looks something like: $$ \begin{equation} \frac{1}{M}\vec{\nabla}_i\cdot\vec{\nabla}_j \end{...
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1answer
198 views

To what extent is the heat in the focal point due to visible light?

When focusing sunlight on a piece of paper, e.g. with magnifying glass, the paper will be charred and might eventually even burn (assuming low cloudiness). To what extent is the heat a result of the ...
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2answers
59 views

How is a capacitor implemented in Kirchoff's Loop Rule?

I'm real stumped here. I may be missing something, but I'm genuinely perplexed as to how one would add a capacitor to the list of elements being added to an equation through Kirchoff's Loop Rule (KVL)...
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1answer
91 views

number density of photons and the total energy of the universe

I was reading over some assignment solutions that my lecturer put up and one of them said that instead of calculating the number of photons in the universe with the familiar method of $\int^{\infty}_0(...
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1answer
55 views

How to analyse the LHC signal for Higgs?

With increasing energy the collision decreases in the plot for signal in LHC. why is that? and at an energy 125GeV the no of events suddenly increases. How this proves that higgs has a mass of 125GeV?
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3answers
56 views

water pipes break when temperature goes down, how to estimate the energy involved?

Normally low temperature is associated with lower energy state and high temperature with higher energy state. There is an apparent paradox when a water pipe breaks due to low temperature: when ...
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2answers
51 views

I am having trouble understanding work and the factor of time

Consider this: 1 kg object vs 1000 kg object No friction applies in my example and the machine I am using is 100% efficient. Some machine using a fuel applies 1 N of force over 1 meter to each object ...
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13answers
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If visible light has more energy than microwaves, why isn't visible light dangerous?

Light waves are a type of electromagnetic wave and they fall between 400-700 nm long. Microwaves are less energetic but seem to be more dangerous than visible light. Is visible light dangerous at all ...
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2answers
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In a masses inelastic collision, K energy convert to heat but velocity remain same. we receive heat without losing velocity? how?

I have read the answer about the energy and momentum conservation question but I have a great question now! Imagine we have two masses which one of them is at rest and another move and collide to the ...