40

I disagree that you feel centrifugal force. A person in a centrifuge actually feels their reaction to the centripetal force. If you sit in a car that is subject to harsh acceleration, you 'feel' as if you are being pushed back in your seat. There is no force pushing you back- it is simply the result of your inertia.


36

A force is fictitious if it doesn't obey Newton's three laws of motion. Recall Newton's first law: The first law states that an object at rest will stay at rest, and an object in motion will stay in motion unless acted on by a net external force. Mathematically, this is equivalent to saying that if the net force on an object is zero, then the velocity of ...


21

In general, taking the non-relativistic limit for a moving particle is to assume that its velocity is much smaller than the speed of light, i.e. that $$\frac{v}{c}\ll 1.$$ In this limit, the laws of Special Relativity coincide with the laws of Newtonian physics, and (most) relativistic effects can be ignored. For example, in Special Relativity the equations ...


20

According to the basic Newtonian formulation of mechanics, "real" forces come in couples: a force (action) and its reaction acting on the source of the action. Furthermore "real" forces are independent of the used reference frame. Fictitious forces, as centrifugal or Coriolis one, violate both conditions. This is the reason why they are ...


12

The object at the non-inertial frame really feels the centrifugal force! So, it is a real force for the object. This is actually incorrect. An accelerometer mounted on the object detects only the sum of the real forces. There is no experiment by which you can “feel” any fictitious force. They only exist in non-inertial frames and their existence or non-...


9

"Fictitious" is a loaded term. It is better to use the alternative terms "pseudo force" or "inertial force", which avoid implying that the force is not real. Whichever label is used the key point is that centrifugal force (and, similarly, Euler force and Coriolis force) arises purely from the fact that we are measuring the ...


5

Without arguing why something is called something, I'll just give the justification for calling something, something. Whenever a force emerges due to our choice of a non-inertial frame, it's called a fictitious force. Consider as an example a person on an upward accelerating lift. If the person relies on his own frame, then he should write the equation of ...


5

The correspondence between ensembles and relevant thermodynamic potentials requires a partial correction. Let me start with a general remark about names. Within thermodynamic, the generic name for a function of state embodying the full information about the system is fundamental equation. Energy as a function of $S,V,N$, is a fundamental equation. Moreover, ...


5

Although it is difficult, I will try to avoid mathematical definitions here. A tensor $T$ is, first and foremost, a geometric object. It lives in a space on its own and bears no reference to anything else. When we choose basis vectors, the tensor $T$ can be expressed as a unique linear combination of the basis. In your example, it is $$T=T_{kl} \mathbf{e}^k \...


4

In special relativity, the total energy of a particle in free space (i.e. in the absence of external fields) is given by: $$\mathrm{E^2 = p^2 c^2 + m^2 c^4}$$ The energy of the particle is therefore dependent on a sum of two quantities, the first being the kinetic energy (which contains the momentum $\mathrm{p}$), and the second being the "rest energy&...


3

An ideal fluid is a fluid that is incompressible and no internal resistance to flow (zero viscosity). In addition ideal fluid particles undergo no rotation about their center of mass (irrotational). An ideal fluid can flow in a circular pattern, but the individual fluid particles are irrotational. Real fluids exhibit all of these properties to some degree, ...


3

For the Anderson localisation-delocalisation transition, the localisation length and the correlation length are used interchangeably. The whole point of a (disorder-induced) localised state is that, by definition, it is not extended, that is it has a finite spatial extent, usually confined/centred onto a single lattice site (image below): If this central ...


2

I copy here from a prominent US university. Particle physics phenomenology is the field of theoretical physics that focuses on the observable consequences of the fundamental particles of Nature and their interactions. The recent discovery of the Higgs boson provides an exquisite confirmation of the Standard Model, but important mysteries remain, including ...


2

A perfect, or ideal fluid is also incompressible, but an ideal gas is not. Pressure and volume changes on an ideal gas can cause changes in its density. A perfect fluid is described by an irrotational velocity vector field $\bf v$, so that $$\nabla \times \bf{v} =0$$ and this is not necessarily true for ideal gases. The molecules of an ideal gas interact ...


1

Black body radiation is the maximal possible thermal radiation ($\varepsilon = 1$). Real bodies are not perfect BBs, so the most primitive factor taking this into account is $\varepsilon \le 1$. It a factor (multiplier) at the specrtal curve.


1

I am guessing it is the emissivity which is a factor that you multiply by the curve because things are not perfect blackbodies, depending on what the surface is made of.


1

Contrarily to the existing answers, and to the citation in one of them, the terminology is not uniform. According to the answer to a previous similar question and to Landau&Lifshitz textbook on Mechanics of Fluids, a perfect fluid is a fluid described by the Euler equation, continuity equation, without viscosity and thermal conduction. It may be ...


1

I am not sure to say whether this is called a 'multi-layer pulley'. But as you can see there are only three pulleys labelled as 'A','B' and 'C' in this figure. Probably, pulley 'B' consists of two disks welded together. And I am here trying to answer your second question. ...which circle is counted as its size? This question shouldn't be asked. First you ...


1

From S it would seem that time is going slower for S′. Surprisingly, it would seem from S′ that time is going slower for S as well. Now, who is right? Answer: Both of them are right. So, is it really right to call centrifugal force fictitious just because it doesn't exist in an inertial reference frame? S and S' don't disagree on how fast time is passing. ...


1

Imagine standing on a train where the floor is made of ice. The train is parked at the station. You are standing on the ice floor of the train, holding onto nothing. There are other passengers seated on the train. As the train pulls out of the station, you stay in place inertially, because the ice provides no shear force to your feet due to a lack of ...


1

"The object at the non-inertial frame really feels the centrifugal force! So, it is a real force for the object." Three points on this: This is a philosophical observation, not physical. Which does not mean it is invalid. It's just that all kinds of mischief arise when people confuse philosophical statements with physical statements. In physics, ...


1

the object feels there is a radially outward force No, it does not, and this is the whole reason behind the misconception. A human may feel this way, but this is a thing that goes on in your head, and simply means that we are not wired in a way that we can really process the forces at play in a meaningful way on a biological level - mostly because it never ...


1

So, is it really right to call centrifugal force fictitious just because it doesn't exist in an inertial reference frame? Fictitious forces only exist in non-inertial frames. Reactive centrifugal force (or whatever term you want to call it) is real and part of a pair of Newton third law forces. Consider a puck sliding on a frictionless surface, being ...


1

$mg_0$ is apparently the difference between the kinetic momentum $m\dot{x}$ and the canonical/conjugate momentum $p$. However if the perturbation $g_0,g_1$ does not preserve the canonical structure, i.e. descend from an interaction Hamiltonian, then the notion of canonical/conjugate momentum is not well-defined.


1

But watching car videos or such, people also say "10 ft-lbs OF TORQUE".....isn't that redundant? It is necessary to specify torque since ft-lbs is also a unit for work which is not the same thing as torque. Hope this helps.


1

It is because pound-feet correspond to torque, but not only torque. Energy has the same physical dimension of $\mathrm{kg \cdot m^2 \cdot s^{-2}}$ or $\mathrm{lbs \cdot ft^2\cdot s^{-2}}$, yet they are not directly comparable. In case of torque this is the result of a cross product of two vectors $\vec{r} \times \vec{F}$ (length of the lever arm multiplied ...


1

It's convention and a judgement about whether the meaning will be clear if we state a quantity without also stating its meaning. We also might say the engine has "2 liters displacement" (rather than just "2 liters"), or "200 braking horsepower" (rather than just "200 hp"). On the other hand if we say a milk jug has &...


1

Yeah, it's because of the other useful quantities which have those units.


1

This is semantics, not physics. Whether you call it “rotation,” “circular motion,” “circular rotation,” “circulation,” “circumambulation,” “rotary motion,” or any other permutation/synonym, the key is to clearly define what you mean. That way, everyone can be clear about the physics, regardless of their semantic opinions. I recommend you focus on ...


1

What is the difference between circular motion and rotation? Basically, the difference is that in circular motion, an object just moves in a circle. In rotational motion, the object rotates about an axis passing through the object. That said, you can have both rotation and circular motion associated with a rigid body. Consider some arbitrarily shaped rigid ...


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