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.

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Aircraft lift theory vs energy conservation [closed]

I spent years trying to find out that when an aircraft flies or anything works it consumes energy more than it delivers back, means no perpetual motion exists. My query is that when an aircraft is at ...
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4answers
161 views

Why current loses its energy?

Can someone explain or give a link to explanation why current looses its energy? For example in simple circuit with lamp. I understand that the energy is spent for heating and lighting. But how ...
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What is the energy source if a tall water tank is used to transfer floating objects upwards instead of cables with motors?

Suppose I want to transport some logs from the ground to the roof of a tower. Originally I can use a lift, or some cables, or even move the logs upwards manually; then the energy is converted to the ...
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1answer
82 views

Change of internal energy to kinetic energy

Why do we feel tired while running as during running we are increasing our kinetic energy. I understand that the energy inside us(from food or something else) is being converted to KE while running ...
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1answer
31 views

Can Charged Virtual Particle Interactions Propagate Electromagnetic Energy?

Since virtual particles have charge and motion, their fields should interact with each other to produce Lorentz forces, even in a perfect vacuum. Can these interactions propagate energy that is ...
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120 views

Dilemma About Energy : Can You EXPLAIN? [closed]

PROBLEM 1 : A 2.14 kg block is dropped from a height of 43.6 cm onto a spring of force constant k = 18.6 N/cm as shown in fig:12-19.find the maximum distance the spring will be compressed. solution ...
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1answer
69 views

When a photon escapes a black hole, why is it red shifted? [duplicate]

I think that is how astronomers hunt for these elusive objects using radio telescope and also gravitational lensing, I'm wondering how these photons lose their energy while encountering black hole or ...
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5answers
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Can we create and destroy energy simultaneously at different points in a space?

Can we create an amount of energy at a point in space and destroy an equal amount of energy at another point in space, with both the processes occurring simultaneously? This will not violate energy ...
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2answers
117 views

Why is the object's maximum speed at $x=0$ for spring?

My book derives velocity of the hanging object of a horizontal spring (on frictionless surface) as a function position: $$v=\pm \sqrt{\frac{k}{m}(A^2-x^2)}$$ and shows the maximum speed is at when x ...
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1answer
100 views

Conservation of energy during the flight of a fire cracker [closed]

We say that energy is neither created or destroyed. It can only be transformed. I hope this principle is applied in the flight of a fire cracker. The chemical energy is converted into physical energy ...
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0answers
34 views

Quantum Fluctuations [duplicate]

Energy is converted to mass and mass to energy. But during quantum fluctuations energy is created without mass, does this not violate the law of conservation of mass and energy?
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4answers
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Why do many people say that virtual particles do not conserve energy?

I've seen this claim made all over the Internet. It's on Wikipedia. It's in John Baez's FAQ on virtual particles, it's in many popular books. I've even seen it mentioned offhand in academic papers. ...
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2answers
122 views

What happens when two bodies collide in a dynamics point of view?

I'm a high school student learning about energy and momentum. What confuses me is the things with elastic and inelastic collisions. I completely (in my opinion) understand those concepts in energy ...
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1answer
30 views

How do i find how long an object can coast for?

I am given the mass of an object (a motorcycle), its velocity, the mass of its wheels, and the radius of the wheels. If the object rolls without slipping, how can I possibly find out how high it can ...
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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, ...
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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 ...
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1answer
59 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?
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0answers
60 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 ...
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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, ...
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1answer
109 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 ...
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1answer
95 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.
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1answer
51 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 ...
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1answer
61 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 ...
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1answer
124 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 ...
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1answer
91 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 ...
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2answers
87 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 ...
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1answer
104 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 ...
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2answers
428 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 ...
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1answer
50 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
53 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 ...
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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 ...
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4answers
68 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 ...
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2answers
113 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 ...
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1answer
33 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 ...
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2answers
186 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. ...
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4answers
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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 ...
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3answers
151 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 ...
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2answers
67 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 ...
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2answers
62 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 ...
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2answers
43 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 ...
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1answer
91 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 ...
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1answer
128 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} ...
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0answers
76 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 ...
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1answer
49 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 ...
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1answer
123 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 ...
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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
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2answers
163 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 ...
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1answer
271 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 ...
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1answer
41 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 ...
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4answers
472 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 ...