# Tag Info

### Internal work in system made up of a ball and the earth

Work of a force is defined as that force times (vector dot product) with displacement of the material object it acts on: $\Delta W = \mathbf F \cdot \Delta \mathbf r$. Sign of this quantity is ...
1 vote

### Thought experiment: Where does potential energy come from if matter is created from energy?

I think the OP could basically be describing a Kugelblitz$^†$ formed by light rays coming from nearly all directions, focused on the point in question, which is a physical scenario. My attempt at ...

### Thought experiment: Where does potential energy come from if matter is created from energy?

There are many things wrong with this question. Unfortunately, the only way to answer it is to correct the problems: Assume that I have a slightly magic machine that can create any amount of matter ...

### Force on Dielectric on pulling it out from capacitor

Well, let's try and recreate the equation. We know that the standard, or at least, most accessible way to obtain the force on a dielectric as it is being inserted into/removed from a capacitor is to ...

### Is it possible to generate electricity perpetually using only permanent magnets?

12.01.23 think outside the box. the "law of conservation of energy" is a lie. why? well look around you. obviously the universe which - is made of matter and every was created. so energy ...

### Do virtual particles actually physically exist?

Under the context and physical definition that theoretically these particles cannot be ever detected directly because their unstable nature and very tiny lifetime which is within the Heisenberg ...

### A Jet of Steam passed into a Block of Ice

Just before all the ice had melted, the temperature of the mixture of water and ice was 0 C. So, when the final bit of ice melts, the temperature will be 0 C.

### During fusion, how does mass turn into energy?

There is no reason to call mass-energy conversion as merely as popular science Experimental measurements of masses: ...

### How can the energy of a system increase even if net work done on it is zero?

This will result in increased kinetic energy of the blocks, thus result in an increase in the total energy of the system. is a correct statement but must include an extra word, $\dots$ increase in the ...
1 vote
Accepted

### How can the energy of a system increase even if net work done on it is zero?

In $W=\vec F \cdot \vec s$ the $\vec F$ is a force acting on the system and $\vec s$ is the displacement of the material of the system where the force is acting. So in your example both forces are ...

### How can the energy of a system increase even if net work done on it is zero?

Either the pair of blocks are one thing, in which case the one thing's kinetic energy is the kinetic energy associated with the translation of the center of mass of the pair of blocks, which doesn't ...
Accepted

### During fusion, how does mass turn into energy?

Your explanation vis a vis the strong force and the Coulomb barrier is spot-on conceptually, and you've discovered that there is no reason to invoke "mass energy conversion." Indeed, I ...

### Total energy of a rocket launch

For a chemical rocket, the energy source is chemical energy. This energy becomes thermal and kinetic energy of the ejected propellant and of the rocket itself. As the rocket moves upward from the pad, ...

### Total energy of a rocket launch

It then launches, and both KE and PE start to increase. How does this obey conservation of energy? You forgot thermal energy and chemical potential energy, etc. Thermal energy also increases, but ...

### How is energy conserved in formation of chemical bonds?

You are basically correct. The kinetic energy of the newly formed water molecules is by definition heat. The radiation observed is emitted after the reaction as the product ($H_{2}O$) cools. Here's ...
Accepted

### Energy conservation in dipole capacitor interactions

they still have the velocity gained by the two additional capacitors but none of the three capacitors lose their charge. The dipole gains some kinetic energy so where does the energy come from? ...

### How is energy conserved in formation of chemical bonds?

As you know, the formation of chemical bonds comes with a spontaneous release of energy. This is is in the form of electromagnetic radiation of wavelength matching the energy gap between the lowest-...
Accepted

### How does the excess GPE of a mountain cause its base to melt?

However, does there exist a physical explanation of how this occurs, not just one based on the conservation of energy From Weisskopf's response to comments: I have used the melting heat...as a ...

### Parallel plate capacitor infinite energy

A system's energy, which is conserved when the system is closed, is the sum of the kinetic and potential energy. You've forgot to take the potential energy, namely $\Delta x Eq$, into account.

### Parallel plate capacitor infinite energy

Let's say the capacitor has voltage $V$ and charge $Q = CV$. Let's assume that a positive charge $+q$ and a negative charge $-q$ are created halfway between the plates, with $q\ll Q$ (and equal mass, ...
Accepted

### Is total energy conserved in a reversed Hooke's law $F=+k x$ problem?

The following case is similar to the harmonic motion differential equation, however, the minus sign changes the problem \begin{align} m \frac{d^2x}{d t^2}-k x =0 \end{align} Now, the question is ...
1 vote
Accepted

### With regard to Mechanical Energy what forms of Potential energy are included?

I've seen the mechanical energy of a system defined as the sum of its kinetic and potential energies. What forms of potential energy are included in this definition? Gravitational and elastic ...

### Three masses connected by a string (momentum conservation)

Note sure why you think A will collide with B, or what "collide without contact" means. My interpretation of the scenario is that B moves in the positive $y$ direction, A and C are pulled ...
Accepted

### Three masses connected by a string (momentum conservation)

Firstly, the net external force acting on the system (all 3 bodies) is zero, which means that you are free to use the laws of conservation of energy and momentum. You need to understand that the ...
1 vote

### What distance to use when calculating work?

For the calculation of work done by a Constant Force, we generally use $W = \vec{F} . \vec{S}$, Where $\vec{S}$ being the The amount of displacement of the object while the force is/was being applied, ...
1 vote
Accepted

### What distance to use when calculating work?

It is never the source (the "applier") that we consider. We only consider the properties of the object that is being influenced. In all laws and relationships (just think Newton's laws of ...
1 vote

### What distance to use when calculating work?

In the equation $W = \vec{F}.\vec{s}$, the term $s$ refers to the displacement of the object on which the force is applied. Then when climbing up stairs, I would be moving relative to the stairs and ...

### Is it possible to generate electricity perpetually using only permanent magnets?

When you add a (theoretical) 100% SHUNT material thin enough between two magnets in a series, you can split the magnetic field in half and redirect it so that the other magnets can push beyond the ...
1 vote

### Work done by a moving normal force

The easiest formula to use is typically $$P=\vec F \cdot \vec v$$ where $P$ (power) is the rate of work done by force $\vec F$ acting on the system at a point where the material of the system is ...
1 vote

### Work done by a moving normal force

To calculate the work done by a person (or a $100\%$ efficient machine) climbing a moving escalator, replace $mgh$ by $mgh'$ where $h'$ is the vertical distance that they have climbed relative to the ...
Given the Lagrangian \begin{equation} L(q,\dot{q},t)= \frac{\dot{q}^2}{q}-V(q) + \dot{q} t + q \end{equation} depending on the generalized coordinate $q(t)$, its total time derivative $\dot{q}(t)$ and ...