The law of conservation of energy, which states that the amount of energy in a system is constant. For questions about Earth's environment, see the climate-science tag instead.

learn more… | top users | synonyms

1
vote
0answers
58 views

First law of thermodynamics with additional term

I read in a paper that a "known expression for the heat received by a body" is $$dQ=dU+pdV-\mathbf{v}\cdot d\mathbf{P}$$ where $\mathbf{P}$ is the linear momentum of the body, $p$ is the pressure, ...
1
vote
3answers
138 views

General Definition of Steady State

According to many sources (including Wikipedia, Stephani&Kluge, D.J. Acheson) a steady state ist: In systems theory, a system in a steady state has numerous properties that are unchanging in ...
2
votes
1answer
58 views

Why do tidal forces not violate conservation of energy? [duplicate]

Europa is an example of a satellite which is heated by tidal forces. The orbit is constant, so how is energy conserved on Europa?
0
votes
0answers
55 views

Why on a frictionless incline, a rolling object reaches the bottom slower than an non-rolling object?

I am really sure if what my physics teacher told me was correct. But he said, rolling objects has rotational kinetic energy, so not all potential energy they have at the start is converted into ...
-3
votes
1answer
67 views

Do you know the principle which says that connecting two sources of similar kind produces a waste and destruction? [closed]

There is a great article, called commutation cells, which states that you cannot transfer kinetic energy from one container to another immediately, bypassing the potential energy storage. Otherwise, ...
1
vote
1answer
97 views

How much work can the human body do before dying of exhaustion [closed]

If we could assume: We don't increase our energy from absorbing food. Our human example in scope isn't starving or suffering from malnutrition. I mean how much work can we do until the body would ...
1
vote
1answer
85 views

I m just try to make Free energy using buoyancy [duplicate]

Can I make power (electricity ) using buoyancy see diagram. if this diagram is possible then how much power i get . I just need formula for upwards speed.
1
vote
1answer
49 views

Minimum energy required to remove the satellite from its orbit to infinity?

My book says that minimum energy required to remove the satellite from its orbit is equal to its total energy (K.E+P.E). But shouldn't it equal to only the potential energy difference of satellite in ...
1
vote
1answer
57 views

Energy paradox in fluid mechanics

In a fluid, the specific mechanical energy $$e_{mech}= \frac{P}{\rho} + \frac{v^2}{2} + gz$$. Where $P$ is the static pressure, $\rho$ is the density, $v$ is the velocity, $g$ is the gravitational ...
-2
votes
1answer
121 views

Explain this contradiction of violation of “ energy conservation ” using classical mechanics

Consider a rocket moves upward with some acceleration for a very small time say '$dt$' then the kinetic energy increases (for acceleration). as well as as the potential energy increases (due to height ...
1
vote
0answers
34 views

Turning an engine over with engine compression [closed]

When you compress a bicycle pump and seal the opening, the pump will automatically return to it's initial position when you release it. I suppose this is how air suspension works as well? if you ...
2
votes
1answer
82 views

When are energy, mechanical energy, momentum, and angular momentum conserved?

I am in AP Physics and my only real hangup is knowing when the said quantities are conserved. Please define what is the SYSTEM in your answer. I kind of have the basic idea. For example, if there ...
0
votes
2answers
82 views

Given force as function of position, find the total energy as function of time [closed]

Given that the force for a non-linear spring connected to a mass $m$ sitting on a table is $$f(x) = -kx -ax^3,$$ Find the total energy as a function of time $E(t)$. I have no clue where to ...
2
votes
1answer
99 views

Is the Hamiltonian conserved or not?

The question is the very last sentence at the end of this post. In this post, I'll first show that the Hamiltonian is conserved since it does not have explicit dependence on time and then show that ...
1
vote
2answers
364 views

Max extension of spring mass system

While attempting problems of simple harmonic motion I came across this problem, which has gotten me confused. A fixed horizontal spring is stretched by a constant force $F$. I am required to obtain ...
0
votes
1answer
47 views

Applying conservation of energy to a railgun problem?

When a projectile is lunched due to the Lorentz force($F_L$), how can I apply the conservation of energy that the electrical energy inputted to generate the Lorentz force & magnetic field equals ...
2
votes
1answer
50 views

Simple frame of reference problem (conservation of momentum?)

I'm having trouble wrapping my head around a particular concept. Suppose we have a machine that fires balls of speed $u$ at some mass rate $\sigma$ (of units $\frac{kg}{s}$) directly at a car of mass ...
0
votes
0answers
17 views

energy conservation ballistic pendulum appartus

In a ballistic pendulum apparatus, a ball of mass .0659 kg was shot into the pendulum bob, mass .2489kg and .3489m long from the axis of rotation by a spring with constant of 613 +/- 13 N/m^2 that ...
0
votes
4answers
65 views

Must one include friction and gravitational force in the work term?

Example problem: "A sled has an initial velocity up a ramp of 5 m/s, the ramp has an angle of 20 degrees to the horizontal, and the coefficient of dynamic friction between the sled and the plane ...
0
votes
2answers
104 views

Conservation of Mechanical Energy Before and After Impact of a Hammer

If a hammer does work by driving a nail into a wooden board, how does the mechanical energy from right before the hammer hits the nail compare to the mechanical energy after the nail has been driven ...
1
vote
1answer
32 views

Simplified rolling tire problem - hollow shell vs solid?

First off, I don't understand the math formatting thing on here, but none of these formulae are too complicated. Take a tire rolling down a hill with angle t and distance d. Modeling it as a hollow ...
1
vote
2answers
172 views

Conservation of energy and Killing-field

In general relativity we have no general conservation of energy and momentum. But if there exists a Killing-field we can show that this leads to a symmetry in spacetime and so to a conserved quantity. ...
-1
votes
4answers
36 views

Can matter-energy be conserved in an isolated city system?

Assume we have built a city which has no communication with its surroundings. The city is given an initial energy sufficient to sustain itself for an initial time, t. Nothing escapes, even a single ...
1
vote
3answers
124 views

If heat is energy, then why does cooling take energy when it should actually give energy?

Since everything around us isn't absolute zero temperature, and it has heat/energy, then we should be able to use that energy (without temp' difference I mean) and by using that energy (for example ...
0
votes
2answers
66 views

How do gravity anomalies on Earth comply with conservation of energy?

Gravitational acceleration varies from place to place on Earth in a range of about 0.02 percent and is caused by density distributions within the Earth. Imagine an experiment where you move around the ...
1
vote
2answers
61 views

Magnet and needle

When I place a needle near a clamped magnet and let it go, it moves towards the magnet. Since magnetic field cannot work on individual charge particles, we must conclude that the needle loses its ...
0
votes
2answers
40 views

Phsyics Energy Problem + Concept

A simple problem really. Part 1 Suppose a ball ($20. ~kg$) was shot straight up with an initial velocity of $+50~m/s$. a. Assuming that all of the ball's initial $E_k$ was transformed into ...
0
votes
1answer
81 views

How does the tension force of a massless string affect the speed of a mass on its end?

i,j, and k are the unit vectors in the following question, and $\omega$ is the angular velocity. Lets say you have a mass m attached to a mass-less string of length $L$ tied to a peg with no ...
3
votes
1answer
127 views

Orbital equations of motion with respect to energy

Consider the equations of motion of an object in an orbit around a central body. We use an inertial frame originating at centre of mass of the central body: $$ \frac{d\mathbf{r}}{dt} = \mathbf{V} ...
1
vote
0answers
75 views

Uranus, the Physical model to change it's rotation axle

Uranus rotates pretty wierd, it's 90-degrees tilted; Why is Uranus's axis of rotation tilted? The best answer for this is; that at a distant point in its past, Uranus was struck by a very ...
1
vote
1answer
47 views

Effect of redshift on energy conservation [duplicate]

Light coming from galaxies that are going away from us is redshifted. Since the energy of a photon is purely dependent on its frequency one may conclude that the energy of these photons decreases. The ...
0
votes
1answer
116 views

Conservation of energy or conservation of momentum- which one is applicable in this problem?

There was this question from Kleppner and Kolenkow's Classical Mechanics: PROBLEM: And I found its solution from this Link: It is quite an extended solution and I am not drawing you into the ...
-1
votes
1answer
54 views

Graphing $E_p = E_k + E_{rot}$

I am measuring the moment of inertia of a flywheel and using conservation of energy to work out the value (I am ignoring friction). So for the experiment I have to roll the flywheel down a slope (I ...
0
votes
2answers
145 views

What happens to the kinetic energy of a system in a non-elastic collision? [duplicate]

I know that the kinetic energy of a system is NOT conserved in a non-elastic collision. But energy is supposed to be conserved, so where does all that energy go? Is it transformed into other forms ...
1
vote
1answer
252 views

Two bodies connected by a spring

I came across of a problem. It is about two bodies with equal masses connected by a spring with the coefficient $k$ and the length of $l_0$. Suddenly, a constant force $F$ is applied to the first ...
0
votes
1answer
39 views

Counter intuitive temperature readings in my HRV unit (heat transfer)

Based on temperature alone, it appears that I'm gaining more heat than losing in my HRV. What I'm seeing is the warm air leaving my house dropping by 10C, and the cold air coming in rising by 12C. It ...
7
votes
4answers
465 views

Earth's Kinetic energy change

Earth's rotational speed varies. I have checked the data an found following Peaks; Year 1998, 23.May, the Earth rotated in 86400.0023738 seconds. At 9.July the rotation time of the Earth was ...
1
vote
1answer
42 views

About superconductivity

If I take a magnet and a superconductor than it will expel the magnetic field lines of the magnet. now if there is a coil of wire on the other side of the superconductor and i start to warm up the ...
1
vote
1answer
98 views

Why is this nuclear reaction $p\to n+e^++\nu$ forbidden for a free proton? [closed]

Why is this nuclear reaction forbiden for a free proton? $$p\to n+e^++\nu$$ Where $p$ is the proton, $n$ is a neutron, $e^+$ is a positron, and $\nu$ is a neutrino. What i´ve been thinking is because ...
0
votes
1answer
38 views

Non-linear pendulum (Whittaker's treatise on analytical dynamics of particles)

Reading through Whittaker's "treatise on the analytical dynamics of particles and rigid bodies" I have a question regarding his analysis of the simple nonlinear pendulum at chapter IV. At some point ...
1
vote
0answers
22 views

energy conservation in an electric circuit

Define a reactive (lossless) and reciprocal two-port by its impedance matrix $[Z]$, so that $[Z]+[\bar Z] = [0]$ and let the source impedance and open circuit source voltage be $Z_s$ and $V_s$ at ...
4
votes
3answers
2k views

Where does the energy go in a rocket when no work is done?

While playing Kerbal Space Program, I wondered where my chemical energy would go when fired at 90° to the motion. It would do no work on the rocket, but all that energy has to go somewhere, right? ...
-4
votes
1answer
41 views

Simple harmonic motion, maximum kinetic energy [closed]

Why kinetic energy is maximum at mean position?
1
vote
1answer
39 views

Heat, Work and Internal energy in closed systems

This has been troubling me for a while now. I know that the performed work equals $P\Delta V$ for isobaric systems and I know that in isochoric systems no work is done, but how do I find the heat $Q$? ...
-1
votes
1answer
76 views

Work done by gravitational force!

Suppose a ball is $10m$ high from the ground. It will have $E_p = 10mg$. Now, if the ball falls freely then we know $E_k$ will be $0.5mv^2 = E_p$. But it is said that the work done by a force will ...
-2
votes
3answers
98 views

Using Gravity for Infinite energy?

Can gravity be used as an infinite energy source? What if you throw objects down, say a hill, and had a panel on the bottom that would use the force of the fall and convert it to energy? Would this ...
0
votes
2answers
51 views

Why can we find forces like this using energy methods?

Often to calculate forces in complex situations (usually involving complicated mathematics), I have seen various people employ energy methods. The answer comes out correct, but I can't understand why ...
0
votes
1answer
16 views

Solving a first order non linear differential equation in the specific case of the orbit of a particle moving under a central conservative force

Hello it's my first time posting in here and I hope someone in here can help me as my teachers quite dislike questions that aren't specifically in the curriculum. I'm reading About classical mechanics ...
2
votes
3answers
71 views

How to evaluate energy conservation for magnetization?

A permanent magnet can attract a certain magnetic material mass, giving a certain amount of energy $U_{mag}$. If we first use this magnet to magnetize $n$ ferromagnetic pieces, we would have $n$ ...
2
votes
1answer
48 views

Potential Energy in a System and its Relation to the Total Energy

In this answer it was stated that potential energy is a property of a system and not an individual particle. If we have two particles (1 and 2) interacting via a conservative force, we can write an ...