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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189 views
How do I approach this conservation of energy problem, symbolically
In the absence of nonconservative forces such as friction and air resistance, the total mechanical energy in a closed system is conserved. This is why that when I toss an object directly upwards, the ...
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1answer
540 views
Where does the energy come from when a current heats a wire (resistor)?
I'm trying to figure out an example from a textbook (Demtröder -- Experimentalphysik 2, pg. 198) where the energy transport caused by a current is depicted:
Assume you have a wire (with some ...
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2answers
286 views
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1answer
416 views
How much energy can be extracted from hydrogen?
http://en.wikipedia.org/wiki/B-L says that the difference between baryon number and lepton number is conserved. Ordinary hydrogen has one of each, but turning it into helium releases only the binding ...
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3answers
66 views
computer vs heater coil comparison
If I have a computer and a heater coil that consume exactly the same amount of energy, which would be more efficient at heating my room? This is assuming that they both have the same fans and heat ...
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1answer
134 views
Why don't cancelling wavefunctions for two different particles give zero total wavefunction?
Let $\left|a\right>=e^{i(kx-\omega t)}$， $\left|b\right>=-e^{i(kx-\omega t)}$ be two neutral particles in the 1D free space without any interaction. Then ...
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1answer
193 views
Existence Of Electric Field Lines
Can an Electric Field with field lines Like So Exist:
One Of my friends said it couldn't as the field lines here are not conservative ; so it cannot exist ; Is he right?
Or can it be made to ...
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1answer
141 views
How to understand the work-energy theorem?
How to understand the work-energy theorem?
I took a short lecture on physics for engineering last week. The lecturer emphasized that the work done on an object will cause the kinetic energy change as ...
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3answers
186 views
If you could reverse gravity, what velocity would you achieve on leaving Earth?
If you could reverse gravity, to make it repulsive instead of attractive, what velocity would you achieve on leaving Earth? A simple question really, but I have completely forgot how to calculate ...
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1answer
147 views
Man on treadmill and energy/mass conservation
Suppose we put a very obese man inside a large air tight isolated room with a treadmill and he runs on the treadmill for 24 hours and at the end of the day he sees his weight has come down (mostly ...
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1answer
129 views
Kinetic energy transfer in matter annihilation?
What happens to the kinetic energy of matter when it is annihilated? Is it released in the resultant explosion? In that case shouldn't it be $E=(mc^2 + \frac{1}{2} mv^2)$ ?
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1answer
64 views
Infinite reflection of light and the conservation of energy / momentum
First off, I confess I'm no physicist, but I have been asking people with a more extensive knowledge this one question, without a definitive answer so far.
Basically, I'm playing around with the idea ...
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4answers
194 views
Shouldn't the change in kinetic energy be more in a moving elevator from a stationary frame of reference?
Consider an elevator moving down with uniform velocity. A person standing inside watches an object fall from the ceiling of the elevator to the floor. Say the height of the elevator is $h$. Then the ...
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1answer
400 views
Elastic collision in two dimensions
Suppose a particle with mass $m_1$ and speed $v_{1i}$ undergoes an elastic collision with stationary particle of mass $m_2$. After the collision, particle of mass $m_1$ moves with speed $v_{1f}$ in a ...
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1answer
123 views
Understanding Work and the conservation of energy
We have a car with a mass of $780 kg$ with travels with a speed of $50 km/h$. The car brakes and after $4,2m$ is stops completely. Warmth is created. Calculate the friction.
I solved this easily, by ...
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3answers
128 views
Where does the energy for repulsion in charges come from?
If I bring together 2 objects with the same charge, they repel. But even after the repulsion has taken place, there is no loss of charge in the objects. Where does the energy come from then?
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1answer
245 views
Bernoulli equation from energy conservation
I have derived the energy conservation equation:
\begin{equation}
\frac{\partial}{\partial t} \left [ \frac{1}{2} \rho v^2 + \varepsilon + \rho \phi \right ] + \frac{\partial}{\partial x_j} \left [ ...
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1answer
158 views
Would the Moon drift away from the Earth due to extraction of tidal energy? [duplicate]
Possible Duplicate:
Why does the moon drift away from earth?
It seems to me that, due to conservation of energy, the moon would drift away from the Earth if humans began extracting large ...
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1answer
96 views
extracting energy from cosmological expansion
This question is a more concrete reincarnation of an old question about energy conservation in GR.
Are there mechanisms to extract energy from the cosmic rate of expansion? putting some extremely ...
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1answer
206 views
Thermal energy generated due to loss in kinetic energy when observed from two different frames of reference
A body is moving with a velocity $v$ with respect to a frame of reference $S_1$.
It bumps into a very heavy object and comes to rest instantaneously, its kinetic energy
$$\frac{1}{2}mv^2$$
as ...
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1answer
180 views
What “I” should use in Rotational Energy formula $(I \omega^2)/2$
$\text{Rotational Energy} = \frac{1}{2} I \omega^2$. What $I$ should be used?
$I$ as a inertia tensor matrix = stepRotation * inverse moment of inertia * inverse stepRotation;
Or I as moment of ...
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2answers
308 views
Mechanical energy problem - please help
Quite new to all this - simple question.
"A ball starting from rest rolls down a hill and reaches 10m/s at the bottom. If the same ball starts rolling down the hill from an initial velocity of 5m/s, ...
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1answer
133 views
The relation between Hamiltonian and Energy
I know Hamiltonian can be energy and be a constant of motion if and only if:
Lagrangian be time-independent,
potential be independent of velocity,
coordinate be time independent.
Otherwise
...
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1answer
203 views
what happens when I roll a gyroscope along its axis of spin
Say:
I have a gyroscope that is spinning in the xy plane along the z axis.
I then roll its spinning axis by some angle theta
Now I know the gyroscope will resist my attempting to change its axis ...
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1answer
346 views
Conservation of Energy in Special Relativity
In classical Newtonian mechanics, from what I understand, conservation of energy stems from the fact that all known forces are conservative forces,
and vector calculus tells us that they can be ...
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3answers
82 views
Certain material heating water in a recipient
I don't know how to resolve a problem, but I don't want the answer since I'm almost going to have it resolved.
What the problem says is we have 85 liters of water at 7ºC in an iron pot of 29kg. We ...
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3answers
224 views
Is there a measure of internal energy flow?
A system might have internal energy and/or kinetic energy. Kinetic energy in classical mechanics is a form of energy the object has, only because of its relative movement to other objects.
If you ...
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4answers
603 views
Work done by the Magnetic Force
The magnetic part of the Lorentz force acts perpendicular to the charge's velocity, and consequently does zero work on it. Can we extrapolate this statement to say that such a nature of the force ...
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1answer
745 views
How to calculate calorie expidenture from lifting a weight?
Am I correct to say that when a human lifts a dumbbell from, say, 2 feet off the ground to 6 feet off the ground, he will have increased the potential energy of the weight and thus will have burned ...
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1answer
124 views
potential energy of an object due to other two objects
consider object A with mass $m_{A}$ and positional vector $\overrightarrow{r_{A}}$
object B with mass $m_{B}$ and positional vector $\overrightarrow{r_{B}}$
object C with mass $m_{C}$ and positional ...
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0answers
28 views
Energy Conservation [migrated]
I'm working on a time integration scheme for my research. As a result I have come across an interesting phenomena. Somehow, the total energy of the scheme oscillates. At any given time the total ...
2
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2answers
111 views
Elastic collision and spring
Bodies $A$ and $B$ are moving in the same direction in a straight line with a constant velocities on a frictionless surface. The mass and the velocity of $A$ are $2 \text{kg}$ and $10 \text{m/s}$. ...
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0answers
373 views
Bungee jump physics
Question:
A bungee jumper jumps from a bridge. The length of the loose rope is 30 m. When the jumper reach the lowest point possible, the rope stretches 10 m. What is the final stretch of the rope, ...
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1answer
246 views
Finding Speed with the Energy Principle - Nuclear Fission
The question goes along the lines:
Uranium-$236$ fissions when it absorbs a slow-moving neutron. The two fission fragments can be almost any two nuclei whose charges $Q_1$ and $Q_2$ add up to ...
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0answers
52 views
stress work of uniformly deforming continuum
I have a volume which is deforming (using explicit time-integration scheme) uniformly with velocity gradient $L$ and stress tensor $\sigma$. I would like to determine work done by the volume ...
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4answers
851 views
Will a CFL light bulb and an incandescent light bulb produce exactly the same amount of overall temperature increase over time?
Will a CFL light bulb and an incandescent light bulb, in separate respective closed systems, produce exactly the same amount of overall temperature increase over time?
Assume you have two identical ...
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3answers
354 views
Conservation of energy in objects at terminal velocities
In vacuum, object free falling under gravity, the sum of Gravitational Potential Energy(GPE) and Kinetic Energy (KE) is a constant. The GPE is a decreasing side of a quadratic and KE is a increasing ...
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Is the law of conservation of energy still valid?
Is the law of conservation of energy still valid or have there been experiments showing that energy could be created or lost?
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2answers
544 views
When matter and anti-matter collide
Do they create energy? Or do they just disappear with zero energy?
If they create energy when disappearing, that means it takes energy to create them, right?
If they disappear into zero energy, ...
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1answer
163 views
conversion of information to energy [duplicate]
Possible Duplicate:
Maxwell's Demon Constant (information-energy equivalence)
I was reading:
Demonic device converts information to energy : Experiment inspired by a paradox tempts a ...
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3answers
167 views
Neutron decay and electron anti neutrino $n\to p + e + \bar{\nu}_e$
Why do we need neutrino to explain neutron decay?
Is there any evidence regarding existence neutrinos in the context of
$n\to p + e + \bar{\nu}_e$?
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2answers
116 views
Matter - Antimatter Reactory Practicality
With current technology, would the energy released by a matter-antimatter annihilation be more than the energy needed to created the antimatter in the first place? Would it be worth it? Just curious, ...
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3answers
314 views
The “binding energy” of bonded particles adds mass?
This is a follow-up my previous question. Several of the answers indicated that the mass of a particle (atom, proton, etc.) increase with the "binding energy" of it's component particles - the energy ...
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1answer
16k views
Laptop self charge cable? [closed]
Ok this is a really silly question, but I was really curious as to why this wouldnt work. I'm just starting my electricity and magnetism course, so I really dont know much about electricity. I know ...
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1answer
206 views
Energy storage and battery banks [closed]
Why is it not possible to store windfarm energy in battery banks? A lot of energy isn't being used when wind farms are at peak and we have no way of storing it. This is wasteful. So why don't we use ...
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3answers
400 views
Why isn't pressure a measure of energy?
Hey guys, I'm having a problem in understanding the 1st Law of Thermodynamics.
If i would increase the pressure of a closed system by compressing a gas in a cylinder isothermal, the 1.Law states, ...
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1answer
70 views
How to get the new direction of 2 disks colliding?
I'm developing a 2D game including collisions between many disks. I would like to know how I can get the angle corresponding to the new direction of each disk.
For every disk I have this information ...
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4answers
552 views
Does matter with negative mass exist?
Or does it exist mathematically?
Is it really inconsistent with a common-sense, mathematics or known physical laws?
As far as I understand, if it exists, it must be far away from the "positive" ...
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2answers
461 views
Are information conservation and energy conservation related?
as evident from the title, are both, conservation of energy and conservation of information two sides of the same coin??
Is there something more to the hypothesis of hawking's radiation other than ...
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2answers
145 views
Can conservation of energy be applied if trajectory is not smooth?
In this video
http://www.khanacademy.org/video/conservation-of-energy?playlist=Physics
Khan academy explains conservation of energy for a falling object. He looks at an object falling ...
