# Tagged Questions

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.

0answers
34 views

### When should gravitational potential energy be included in the law of conservation of energy

I have a problem that says: A block of mass 0.249 kg is placed on top of a light, vertical spring of force constant 4 975 N/m and pushed downward so that the spring is compressed by 0.090 m. ...
0answers
22 views

### Compare a normal spring and a torsion spring

Consider a torsion spring with a known spring constant $K_c$. I would like to calculate the required $K_l$ for an equivalent linear spring, which would store the same amount of energy when compressed. ...
1answer
122 views

### Do we have a better understanding of what energy is since Feynman's time?

When lecturing about conservation of energy in the 1960s, Richard Feynman remarked: It is important to realize that in physics today, we have no knowledge of what energy is. We do not have a ...
2answers
90 views

### Which coordinate is to be considered for the energy of simple pendulum?

For an simple harmonic oscillator energy can be represented as in picture. Consider in particular picture (b) with the energy as a function of the coordinate $x$. Consider now a simple pendulum. The ...
2answers
59 views

### How does conservation of energy work?

I understand that the law of conservation of energy states that energy cannot be created or destroyed, it can only change from one form to another. This means that the total energy before a certain ...
3answers
80 views

### Zero Potential Energy Change in Raising a Mass

Suppose I am able to lift a body of mass $m$ up using a constant force $F=mg$ so that net acceleration is zero on it. I want to find the potential energy and the total energy of the body when I have ...
2answers
204 views

### Climbing Stairs and Calories Burnt

I climb stairs to work (20 floors) every day . The least amount of work my body is doing by gaining potential energy (P.E) = mgh where m is mass , g is acc. due to gravity and h is height . Assuming ...
1answer
27 views

### The highest photon energy ever measured and transplanckian energies

What is the highest energy of we have measured of a photon by any physical experiment? Has a transplanckian energy photon been measured? Can we study them -if they exist- with special relativity?
1answer
78 views

3answers
61 views

### Using thermal expansion for mechanical work

Assume I could heat up a bar with zero heat loss to the environment. I could then use the thermal expansion to do some work, for example compress a gas. Where does the energy needed for the ...
1answer
50 views

### Lower bound on energy is potential minimum

Suppose we have a particle of mass $m$ that is in an eigenstate $|\psi\rangle$ of the Hamiltonian $\hat{H}=\hat{T}+\hat{V}$, where $\hat{T}$ is the kinetic energy operator and $\hat{V}=V(\hat{r})$ is ...
1answer
21 views

### Kinetic Energy in the Center of Mass Frame

Given two bodies moving along a line, I can find the velocity of the center of mass frame. Taking the time derivative of the Galilean transformation I get $v'=v-v_{cm}$ By definition, the total ...
1answer
49 views

### Why blasts/explosions hurt people

This seems a stupid question i know but can't really understand the physics behind it. Let's imagine i'm 5 meters away from a bomb and it explodes. Putting apart the high speed projectiles behaving as ...
2answers
176 views

### Do all forms of energy fall under kinetic and potential energy?

I know that energy is recognized through motion. Even in the mass-energy equivalence a velocity is present even though it is a rest-energy (Not really sure if this would count as a potential energy ...
1answer
52 views

### How was the concept of work-energy developed? [duplicate]

I doubt that the concept of work-energy was actually discovered this way. However in the algebra based physics book I am reading, work done by a constant net force is defined as $W = fcos \theta s$ ...
1answer
62 views

### what is the energy required to change only direction of a vector? [closed]

Does change in velocity vector change Kinetic energy of a system? Does any energy change when we change direction of a vector of a system?
1answer
21 views

### Calculate the height reached when 1/3 of original Kinetic Energy is lost [closed]

I am sorry for asking this low level question but there is a confusion, I am not overcoming from hours. My book asks me to solve the following problem: When an object is thrown upward, it rises ...
1answer
92 views

### What came before quantum theory?

My professor explained today that the idea behind quantum theory is that particles have quantized energy states. To an undergrad like me, this is kind of strange. Wouldn't it always make sense that a ...
1answer
30 views

### Heat capacity at constant volume and internal energy

I read that heat supplied at constant volume to a system containing ideal gas changes the internal energy of system, i.e $q=nC_v\Delta T=\delta U$ But what happens if I heat a system and change its ...
1answer
22 views

### Rydberg and electrical energy

I am a high school student. This year I learned the Rydberg constant and its use of finding energy of an electron in chemistry, besides in physics I learned to calculate the energies of two loaded ...
1answer
67 views

### What is more important, energy or entropy? [closed]

What decides if something will change or remain the same? Energy or entropy considerations?
1answer
43 views

### Particle in infinite square well with $\langle E \rangle = (1/4) E_1 + (3/4) E_4$

Suppose we have a particle in an infinite square well with $\langle E \rangle = (1/4) E_1 + (3/4) E_4$. I know that I can calculate the uncertainty in the particle's position by \$\sqrt{\langle E^2 \...
2answers
44 views

### What is the sign of the energy exerted by a man sitting in the back of a boat pulling a canoe?

A man sits on the back of a boat pulling a canoe while the boat travels at a constant velocity a certain distance in the positive X direction. The man feels a constant tension in the rope during this ...
1answer
279 views

### What happened to this folded paper in a hydraulic press?

The video below apparently shows a man folding an A3 size piece of paper 7 times, putting it under the hydraulic press each time. After 7 folds, on the last press, the paper sort of explodes. What's ...