11
votes
Does a small domino toppling a large domino violate conservation of energy?
Every domino has potential energy (from being put upright) that is used (converted to kinetic) when it falls. A finger pushing a small one gets added energy from each increasing domino's potential ...
- 209
9
votes
What happens to left-over energy in atomic excitations?
My question then is, what happens if there is energy for, say 2.5 jumps. The electron should jump up two energy levels, but what happens to the 0.5 "jumps" worth of energy?
A photon with ...
- 91.9k
4
votes
Accepted
Does changing the height where an object is placed contradict the Law of Conservation of Energy?
When you lift a box from the floor and put it on an almirah the potential energy of the box increases, but there is no change in its kinetic energy. Is it a violation of conservation of energy?
I ...
- 91.9k
4
votes
Accepted
Minus sign in Force potential relation, a convention?
The usual defination of force in terms of potential energy is
$$\vec F=-\nabla U$$
...However the minus sign over here seems just a convention
Yes. It is a convention. But it is a long-established ...
- 15.7k
3
votes
Minus sign in Force potential relation, a convention?
Consider this example of some field potential energy profile :
Field's potential energy gradient at particular point is a vector which points to zones with higher potential energy (by definition of ...
- 11.1k
3
votes
How does gravitational potential energy work in a very large distance?
The gravitational potential energy is stored in the asteroid and planet system.
Turning the asteroid round makes absolutely no difference to the gravitational potential energy stored by the system as ...
- 91.9k
2
votes
Does the integral of the vis-viva equation have any meaning?
Given any $v(r)$, the integral over space can be transformed as follows,
$$\int v\,\mathrm{d}r=\int v\,\frac{\mathrm{d}r}{\mathrm{d}t}\mathrm{d}t=\int v^2\,\mathrm{d}t.$$
Recalling that kinetic energy ...
- 27.7k
2
votes
Can anyone explain me why this chain does not move?
In a gravitational field, things fall downward under the force of gravity. As they do so, they convert gravitational potential energy into kinetic energy. If we put the chain in place and it ...
- 8,826
2
votes
Twin paradox - how much energy does it take to travel to the future?
Energy is a frame-variant quantity, while the difference in the age between the two twins is an invariant quantity. An invariant quantity cannot be a function of only a frame-variant quantity, so ...
- 91.9k
1
vote
How does gravitational potential energy work in a very large distance?
But when we change the direction of the asteroid slightly towards the planet, we create a situation where the mechanical energy becomes very large and negative
Why do you think this? The total ...
- 38k
1
vote
How does gravitational potential energy work in a very large distance?
The short answer is that the potential energy of gravity (as any other kind of potential energy) is only defined up to an additive constant. In the case of gravitational attraction, it is a very ...
- 171
1
vote
Does the integral of the vis-viva equation have any meaning?
$$\oint v_r \mathrm dr,$$
i.e. the radial component of the velocity integrated around a radial orbit, is a useful quantity, sometimes called the radial action. For example, it is an adiabatic ...
- 2,648
1
vote
Minus sign in Force potential relation, a convention?
We want to uphold the convention that the potential energy is defined such that:
$$U(r)= -\int_{\infty}^{r} \vec{F} \cdot \vec{dr}$$
This convention implies that;
$$\vec{F} = -\nabla U$$
To see this, ...
- 6,311
1
vote
Can a black hole absorb vacuum energy?
Vacuum energy is a concept from quantum field theory, wherein even the "empty" vacuum of space is subject to fluctuations due to the inherent uncertainty in the properties of quantum fields. ...
- 1,356
1
vote
Accepted
Energy transferred to velocity with and without changing reference frames
The amount of energy in the battery available to alter the masses speed IS frame dependent. A joule applied to a slower moving mass has a greater effect on the speed of that mass than when it’s at a ...
1
vote
Energy transferred to velocity with and without changing reference frames
You have explained what is observed in the original frame, all the fuel is burnt and the velocity of the rocket relative to that frame, starting from rest, is $10 \,\rm m/s$ to the right.
Now consider ...
- 91.9k
1
vote
Does a small domino toppling a large domino violate conservation of energy?
Energy should always be considered between two points in time with a fixed reference point. So, first, let's consider before any pushing has occurred and all the dominoes are standing up in order of ...
- 35
1
vote
How can mechanical energy be preserved if the potential energy is negative?
Thus, the potential energy will be negative, but the kinetic energy
cannot be negative.
The potential energy will be negative relative to a point an infinite distance away from the Earth where the ...
- 67.5k
1
vote
Minus sign in Force potential relation, a convention?
Various times that I have tutored physics (way in the past) I use a math analogy to convince someone that the force MUST be the negative of the gradient of the potential function. No conventions need ...
- 1,567
1
vote
Why is angular momentum and energy conserved in a lever but momentum is not? Why the apparently unequal treatment?
Why is angular momentum conserved in general?
You may know that conservation laws come from symmetries of the Lagrangian.
The Lagrangian is symmetric under space translation? The system will conserve ...
- 2,829
1
vote
If mass can be converted to energy then how is it said that energy can't be created?
isn't it the conversion of gravitational energy stored with mass to other forms, so energy is conserved. (I'm not a physicist just studied physics till grade 12)
- 11
1
vote
What happens to half of the energy in a circuit with a capacitor?
I'll answer this Faradian style, without formulæ or integrals.
The question makes a false premise. The battery does not keep a constant voltage. Rather, it "seeks" to keep a constant voltage ...
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