Questions tagged [velocity]

The time rate of change of the position of an object

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2answers
235 views

Understanding group velocity

Group velocity as a concept in Classical Waves confuse me. It's very easy to point out visually, like in this really helpful graphic here. Okay, it's the speed of the moving bulge, which, notably ...
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4answers
253 views

U-turn in Deep Space

While writing a physically realistic game ( "Asteroid Defender" ) a physical question came up whether Diag.1 or Diag.2 or Diag.3, correctly depicts reality. In deep space (away from other celestial ...
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1answer
134 views

Relative speed when getting close to the speed of light

I was thinking about the relative speed of an observation reference frame and an object which has been accelerated to a speed close to the speed of light. I'm by no mean an expert and the last physics ...
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0answers
140 views

Law of motion of accelaration applying average velocity

Consider the law of motion of acceleration: $s=1/2at^2$ Develop the law decomposing the acceleration: $s=1/2 * (V/t) *t^2 = 1/2*(V*t) = V/2 *t$ So we can say that the space is the moltiplication ...
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140 views

Envelope of wavepacket and group velocity

In this answer a possible derivation of the group velocity is provided. It is, anyway, based on the assumption that there will always be a point where all the cosines will sum with the same phase: ...
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0answers
70 views

Validity of the arclength definition of the four-velocity vector

In many textbooks & papers the four-velocity vector has the standard definition $$u^{\mu}=\frac{dx^{\mu}}{d\tau}$$ where $\tau$ is the proper time. However, some textbooks define the four-...
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0answers
46 views

How can the velocity of electrons in graphene be measured?

I'm trying to understand how one can measure the velocity of electrons in graphene, from an experimental point of view. Does anyone have some clue?
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2answers
78 views

Definition of velocity in classical mechanics

Let $(r_1,r_2,r_3)$ be the coordinates of a particle $r$ in the coordinate system $\phi$. Let $\{\hat{e_1},\hat{e_2},\hat{e_3}\}$ be the coordinate basis of $\phi$. Why do we define the velocity $v$ ...
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0answers
63 views

Light Source + Prism in a closed box --> What happens under movement?

Setup: I'm interested in the behaviour of light / the breaking of light in a closed system under movement. I'm sorry in advance if this question is a super-simple, but I just couldn't think of a ...
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3answers
3k views

How does the size of the hole affect the exit velocity?

I took water bottles and drilled several different sizes of holes on the bottom. During the experiment, I found that the water bottle with a smaller hole takes a lot longer time to leak than those ...
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0answers
58 views

Velocity Profile of the Upper Atmosphere

Consider an Earth-Centered Inertial (ECI) frame in which the tangential (to Earth's surface) velocity is measured. Now consider obtaining constant average velocity profiles of the atmosphere as a ...
2
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1answer
198 views

Velocity of water column

If an air filled tube 5 km long with a diameter of 20 m was submerged vertically under water one end 5 km underwater and the other end at the surface, how fast would the water column rise if the ends ...
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0answers
89 views

Why did they use two separate vectors to calculate the magnitude and angle of the initial velocity?

The question/solution are on the attached images. (It's dealing with projectile motion) I already understand how to work out part a, but I'm having trouble understanding why they used the final ...
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0answers
1k views

Lining up fans in a row

Im new to this website, and not extremely educated in the world of physics. I have a very basic (mostly high school, some college) understanding of physics. That being said, I work for the fire ...
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0answers
377 views

Deceleration of spherical particle in fluid

If I know the initial velocity of a particle entering a fluid, how can I calculate its deceleration over time ? What parameters would I need to know ? Viscosity of the fluid, weight of the particle ......
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0answers
94 views

Can a projectile moving at supersonic velocities leave a silhouette in whatever it hits?

I was recently reading this, and Floris's answer confirmed my knowledge that the information of an collision travels at the speed of sound. While I was thinking about that, my mind wandered and I ...
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0answers
269 views

Relativity addition and signs

I have just covered a very brief module on special relativity as a part of my physics course. I have also done some extra reading mostly; Morrin's Classical Mechanics. While I found the book really ...
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0answers
140 views

How to formally write down the Boltzmann equation?

Can someone write down the Boltzmann equation, not neglecting any of the variables of the involved functions and integrals? Specifically, how to concisely capture the "primed" variables in a sensible ...
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0answers
59 views

How do we generalize limitations on the propagation speed of sinusoidal waves to limitations for transmitting any kind of information?

Our calculations on EM waves basically deal with harmonic waves and through such calculations and relations, we derive some relations and limitations for wave like phenomena. Of these relations are ...
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0answers
397 views

Saturn V specific impulse issue in velocity modelling with Tsiolkovsky's equation against actual values?

I've been trying to model the Saturn V's velocity using Tsiolkovsky's ideal rocket equation, and in the process, I think I may have made a mistake with regards to the specific impulse? I've come up ...
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0answers
139 views

What do the components of light velocity look like in polar coordinates?

The Schwarzschild solution makes use of polar coordinates, and I'm wondering how the different components of velocity of light change with the position. Might I get some examples of light velocity ...
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0answers
700 views

Finding the terminal velocity of a magnet dropped in a solenoid

We have to find proportionality of the terminal velocity with the factors of the system: Plot: a small dipole(mass $m$) with dipole moment $\mu$ is dropped in a long solenoid (radius $r$, ...
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0answers
216 views

Is there any place you can safely skydive without a parachute?

While trying to explain to someone how a kitten walked away from a fall from a skyscraper I got to wondering if there's any place a human could do that and I find myself out of my depth. The only ...
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27 views

Relative kinematics curved space

I know that in a general curved manifold it is possible to describe parametric curves. Then, the length of the curve will be a indipendent from the coordinate system used --> the metric tensor ...
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0answers
31 views

Is it possible to find the exact value of the dynamic viscosity of a fluid by applying Stokes' law?

I am a high school student who is investigating the dynamic viscosity of a fluid. Typically, high school physics model the dropping of a spherical object vertically into a viscous fluid with the ...
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25 views

Calculating infinitesimally small volume of a sphere in velocity space

This link (at the end of the page) is deriving the formula to calculate an infinitesimally small volume $dV$ on the surface of a sphere with radius $v$ in velocity space. It states that $dV = ...
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1answer
20 views

Freefall equations and forces

Consider a scenario where a 100kg mass is hanging from a rope. It's stationary, so the force it exerts on the rope is given by $F=ma$, where $a$ is the acceleration due to gravity, which works out to ...
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29 views

How would one calculate velocity with respect to time in Case 2?

Case 1. : The rocket is weightless in space. It's fueled with propellant. It's wet mass is starting mass $m_s$ and dry mass final mass $m_f$. Suppose rocket's initial velociti is 0. The rocket ignites ...
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75 views

Derivation of 4-velocity - where does this equation come from?

I'm a student working through a special relativity book. In a chapter of the book, they are deriving each of the components of a 4-velocity vector in terms of ordinary 3-velocity. (Here $\vec{x}$ ...
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39 views

What is rate of heat produced in terms of radius $r$ in viscous liquid under gravity?

what is the dependency of the rate of heat produced in terms of radius $r$ after the drop attains terminal velocity when A small ball of radius $r$ is falling in a viscous liquid under gravity? My ...
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42 views

PG-Metric dr/dt

at the moment, I investigate some time in learning General Relativity and there I saw the Painlevé-Gullstrand Metric which is given as $ds^2 = -dT^2 + \left(dr+\sqrt{\frac{r_s}{r}} dT\right)^2 + r^2 ...
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1answer
30 views

How do we write free body diagram for an object that is rebounding?

How do we write free body diagram for an object that is rebounding? Here's an illustrated example Let us assume that the object has an initial force. So, I want to draw free body diagram for each ...
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25 views

When is the group velocity of a wave packet the velocity of energy flow?

In particular, I'm asking this for anisotropic media
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1answer
35 views

Forces between wheels and road for a vehicle

Let’s assume we have a front-wheel drive (FWD) car, and we apply a torque (Cf) to the front wheels. At this point, assuming no slip condition, a friction force (Tf) will occur due to friction between ...
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0answers
37 views

Correlation between velocity and homogeneity of spacetime and isotropy of space

Considering only inertial frames of reference and constant velocities, does the fact that any velocity, with the exception for the speed of light in a vacuum, can be transformed, via an accurate ...
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0answers
29 views

Minimum Time Through Curve

Consider the following conditions: A level road with the path $\vec{r} = \left<x(s),\ y(s)\right>$ A max speed of $v_{max}$ A vehicle with the mass $m$ Tires with a static friction coefficient ...
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0answers
191 views

Gravity and rotating torus

Questions: Would a spinning torus lose its weight? Would a solid torus, spinning at 7,81 km/s radial speed completely loose it's weight on Earth-like object? Would it 'fly away' at higher speeds? {...
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1answer
35 views

Can Mach Number Decrease while Flow Velocity Increases?

As in the question statement, I am wondering whether it is possible for Mach number to increase while local flow velocity decreases. I am basing myself on the simple case of an ideal gas, in which: $$...
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0answers
67 views

About the convective constancy of Clebsch potentials

For a fluid with non-zero vorticity, the following representation for the velocity in terms of scalar variables is well-known: $$ \vec{v}=\vec{\nabla}\phi +\beta\vec{\nabla}{\gamma} $$ It is called ...
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0answers
229 views

How can I calculate the sensitivity of a seismometer?

I would like to know how to find the minimum ground motion a seismometer can measure, specifically if a certain seismometer can measure 1 micron/sec velocity. I have a few specs from the datasheet but ...
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0answers
149 views

Calculating circle rebound

I'm computational modelling circular collisions. I have the x-y components of the circles' velocity vectors (green lines) I'm trying to calculate the resultant rebound velocities When the collision ...
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0answers
254 views

Emperically Determining Terminal Velocity of a Sphere Falling over Critical Mach Number

I originally thought that the terminal velocity of a smooth sphere in free fall through the atmosphere would be an easy question to answer. But for heavy spheres of small diameter, the terminal ...
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0answers
48 views

Is it the case that vector quantities always have to do with location?

We know that vector quantities follow vector law of addition and vector addition only makes sense in a plane/space (we can treat vector addition in a line as scalar addition). It is also worth noting ...
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0answers
168 views

Doppler effect for a driver of an ambulance

Im thinking about Doppler effect more than I should, because it makes me crazy now. Anyway, here is the question. Does a driver of an ambulance hear a lower frequency of his horn, than it actually ...
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0answers
165 views

What is 3-Force and 3-acceleration?

I can't seem to find any information related to the 3-Force or the 3-acceleration, only for the 4-force and 4-acceleration. Could someone explain the difference? The context is that I'm trying to ...
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1answer
31 views

Comparing the energies needed to reach the same relative velocity

I have a beam of particles being accelerated up to an energy $E$ and hitting a stationary target. I have 2 other beams pointed at each other and each one accelerates their respective particles up to $...
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0answers
24 views

Is the rotational velocity of a vortex consistent across its height?

I am trying to locate information about calculating the rotational velocity of a vortex. Is the velocity at the vertex maintained across the entire vertical height of the vortex? As the radius ...
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0answers
633 views

Calculation of longitudinal stress in a pipe segment

As part of a simulation model, I need to calculate the derivative of the longitudinal stress in a segment of a long thick-walled pipe. The pipe is vertical and submerged with the same fluid on the ...
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0answers
340 views

How to determine the three-velocity measured by a single observer?

In this question the issue of extracting the three-velocity of a test particle in some frame arose. The answer provided by @PaulT and in this paper (arXiv) seems to me to give rise to ambiguity when ...
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0answers
190 views

Meaning of a Dirac delta speed in 1d shallow-water equations

A 1d thin layer of a fluid of constant density in hydrostatic balance can be modeled by shallow-water equations: $$\begin{align*}\partial_tu+\partial_x\left(v+\frac{u^2}{2}\right)&=0,\\ \...