Activity for celtschk‭

Type	On...	Excerpt	Status	Date
Answer	—	A: maxwell equation in 1d Yes, that would the obvious interpretation of that equation in one dimension. Note also that in that case, the divergence also reduces to the ordinary derivative. In other words, in one dimension, the electric field is constant wherever there is no charge, and if we additionally demand that the el... (more)	—	over 1 year ago
Answer	—	A: How can the kinetic energy equation be intuitively understood? Change in momentum is force times time. On the other hand, change in kinetic energy is force times distance (more accurately, the component of the force along the movement times distance; a force perpendicular to the movement doesn't change the energy). Now imagine you apply a force for a given ti... (more)	—	over 2 years ago
Answer	—	A: Clear up confusion on Minkowski signature As you probably know, one of the postulates Einstein's Special Relativity is based on is that all observers see light in vacuum go at the same speed $c$. Now consider a lamp at rest relative to John being switched on. The light is going through vacuum from then on, until after some time it arrives... (more)	—	over 2 years ago
Answer	—	A: Should I always write units in equation no matter if it looks like variable? In short: Yes. And there are standard ways to distinguish variables from units. Let me explain in detail. In physics, we deal with physical properties of objects and systems. Those quantities can be split down into quantites, that is, properties that can be quantified. To quantify basically means ... (more)	—	over 2 years ago
Answer	—	A: Find equation of motion using. Lagrangian given equation is $L'=\frac{m}{2}(a\dot{x}^2+2b\dot{x}{y}+c\dot{y}^2)-\frac{k}{2}(ax^2+2bxy+cy^2)$ Your mistake is that you did a second derivative of $L$, taking the derivative according to both degrees of freedom together. Instead you need to make a separate equation for each degree of freedom. Since you have two degrees of freedom ($x,y$), you get two equations: \begin{align} \frac{\math... (more)	—	over 2 years ago
Answer	—	A: Prove differential form of Lagrangian Let's first remember how you check that you are at an extremum (minimum, maximum, saddle point) of a normal differentiable function. You do so by checking that the first derivative is zero (plus further tests that are irrelevant for the current question). Now what does the derivative being zero me... (more)	—	over 2 years ago
Answer	—	A: Why we can't find a particle accelerating unless there's some other particle accelerating somewhere else? If you are accelerating while running on Earth, actually you are also accelerating Earth in the opposite direction. However for a given force, the acceleration is inversely proportional to mass, therefore when some $60\\,\rm kg$ person accelerates by, say, $1\\,\rm m/s^2$, then Earth, which has a mas... (more)	—	over 2 years ago
Answer	—	A: How to find position of a particle at a time given a position dependent force In general, the only way to do it is to solve the equation of motion. In simple cases, that can be done analytically (that is, you can find an explicit formula, but in most cases (outside problems given to students) you have to either make approximations (that is, essentially find a sufficiently clos... (more)	—	over 2 years ago
Answer	—	A: What is the meaning that the universe is flat? To understand this, it helps to look at a dimension less. Imagine, you're having a dispute with a flat-earther about whether the earth is a sphere or a flat plane. Moreover, there's a third person who holds the position that the earth is actually shaped like a saddle. As an additional problem, ... (more)	—	over 2 years ago
Answer	—	A: What is inflation in cosmology? Inflation in cosmology refers to a phase of the early universe where the universe expanded extremely fast. And the universe expanding quite literally means the space getting bigger. As you noticed, cosmic inflation does not refer to just any expansion of the universe. The universe is still expandi... (more)	—	almost 3 years ago
Answer	—	A: Would we need Alternating Current if superconducting wires existed? The major advantage of AC is that is can be easily transformed to different voltages. This is important because current transport is most efficient if the currents are low (because the losses are proportional to the square of the current), and this is achieved by making the voltage high for transmiss... (more)	—	about 3 years ago
Question	—	Unusual way to write spacetime coordinates/metric: Is there any downside? In special relativity, spacetime coordinates are normally given as $$(ct, x, y, z) \tag{S}$$ with the metric being either $$g = \operatorname{diag}(-1,1,1,1) \tag{+}$$ or $$g = \operatorname{diag}(1,-1,-1,-1) \tag{$-$}$$ depending on which sign convention the author prefers (the second one seem... (more)	—	over 3 years ago