Questions tagged [velocity]

The time rate of change of the position of an object

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Calculating velocity of particle rotating in circular disc [closed]

In this, the final velocity will be the vector sum of tangential velocity and the velocity with which it is moving out of the disc. The tangential velocity will be $\omega R$ and for finding the ...
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Does acceleration acting on velocity only change direction or magnitude both? [duplicate]

Recently, I came across a text of a book saying that acceleration acting perpendicular to a velocity only changes the direction of final velocity and not the magnitude. But according to my ...
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How do you show that the temporal part of an object's 4-velocity is decreasing as that object approaches the speed of light? [closed]

As a moving object approaches the speed of light then the temporal component of its 4-velocity should be decreasing. How do you derive and show that this is what is occurring?
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Water tower hydro generator? [closed]

$500$ gallons, $100$ feet high, at tank $10$ inch pipe, every $4$ feet a reduction of $2$ inch pipe diameter, ending in $1/4$ inch tubing to jet nozzles, each nozzle would spin an independent ...
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A Conflict Between Coordinate and Proper Relative Velocities?

Are we forced to conclude that a muon created in the earth's atmosphere has a coordinate relative velocity that is always $\gamma^2$ greater than its proper relative velocity? Consider an “average” ...
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Why do my equations say that an object thrown at $30^o$ with velocity 30 m/s has a $y$ velocity of 15 m/s? [closed]

I don't know if I have stumbled upon a genuine truth, or if I'm doing something very wrong. But here is my problem: I am modelling the 2D trajectory of an object with constant acceleration using ...
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Curl of a velocity [closed]

In classical mechanics, is the curl of $\vec{v}$ always zero? As $\nabla$ is in position space and not in velocity space ($\nabla_v$). What am I missing regarding $\nabla$ operator in different spaces?...
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Speedometer Dilemma [closed]

This is what is written in Resnick Halliday Krane Physics Vol.1 The speedometer of a car indicates it's speed, not it's velocity, because it does not specify a direction. Speed is a scalar, since it ...
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Velocity reciprocity - experimental evidence

Velocity reciprocity means that the velocity $v$ of a reference frame $R$ with respect to another reference reference frame $R'$ is the opposite of the velocity $v'$ of $R'$ with respect to $R$, i.e. $...
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Running deceleration after instant force [closed]

Given a person can run at 10 metres per second. If they are moved to 100 metres per second with an instant force, I'm trying to understand 3 cases of movement. Case 1, the person doesn't apply any ...
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Given *an* expression for the current and *the* expression for a density, can you determine the velocity field?

Suppose you a density field $\rho(\vec r)$ and, due to some equation of motion, you have derived that $$ \partial_t \rho + \nabla \cdot \vec J = 0, \tag{1} $$ where $\partial_t = \frac{\partial}{\...
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Velocity at a given time with known force, drag, area and mass

I am trying to plot the speed of an object of known mass, area and drag coefficient in a given density of fluid. I have correctly calculated the terminal velocity by $$v_t=\sqrt{\frac{2[Force]}{\rho[...
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Basics | Does the velocity in throwing direction change [closed]

Disregarding air resistance. The mass of the ball is centered, not inequally distributed, it can be seen as one mass point for this question! The ball is thrown on earth, just to be exact. When ...
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Why velocity across the actuator disc is constant: Assumption or a result of continuity equation?

In the context of actuator disc theory, we can find the following quote from that article: The rotor is modeled as an infinitely thin disc, inducing a constant velocity along the axis of rotation. I ...
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Spaceships with relativistic instruments

I wonder if it is possible, for future spaceships, to have somekind of instruments on board, that will tell the pilot what his true speed through spacetime is and how much time dilation he is ...
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What is the difference between |$\frac{ d\vec{r}}{dt}$| and $\frac{d|\vec{r}|}{dt}$? [duplicate]

let $\vec{r}$ be the position vector. $\frac{d\vec{r}}{dt}$ will be the velocity. But what is the difference between |$\frac{ d\vec{r}}{dt}$| and $\frac{d|\vec{r}|}{dt}$ ? Do both of them mean the ...
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The acceleration of a particle of a continuum; $\frac{\partial v_i}{\partial t}$ vs $\frac{\mathrm{d}v_i}{\mathrm{d}t}$

Assume that the particles of a continuum body $\mathscr{B}$ with mass $\mathscr{M}$ are labeled by vectors $X_i$; then the momentum balance equation reads $$ F_j = \int_{\mathscr{M}} a_j \mathrm{d}m $$...
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4-velocity in Schwarzschild metric

Is 4-velocity always equal to light speed in any metric? In Schwarzschild metric, the light speed with respect to a remote observer is $1 - r_{S}/r$. Should that be the 4-velocity of a falling ...
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Why is force not dependent upon velocity but on acceleration?

Force is not dependent upon velocity but on acceleration but acceleration is dependent upon velocity, What i mean is a=change in velocity/change in time.So in order to calculate acceleration i need ...
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Can our time dilation be negated by travelling opposite our aggregated velocity? [closed]

Is there such a thing as absolute velocity, and if so, can we negate the effects of time dilation by traveling in the opposite direction? Assuming there is absolute velocity, if we were to move an ...
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How can I use an anti-derivative (integral) to find the velocity, given the acceleration? [closed]

How can I write my acceleration as a function of time given its acceleration? Say a particle has an acceleration $a$ and an initial velocity $v_0$ at time $t = 0$. What is the particle's velocity at a ...
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A numerical regarding relative velocity [closed]

So the question goes, there is a river of width $w$ and there are two swimmers $A$ and $B$, both of whom swim at a velocity of $7.5km/h$ with respect to the river. The river is flowing at $2km/h$. ...
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Special Relativity and Light [duplicate]

I just started learning about relativity in my physics class and would like some help understanding the concepts. My question is imagine two objects start emitting light and are 1 lightyear away from ...
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Confused about flux transport

I am confused about a very simple thing: Let's assume you have a 1D flow (fluid), where your flow velocity v$_x (x)$ = -$\frac{1}{x} \hat{x}$, i.e. your speed (= |velocity|) increases as you approach ...
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If velocity $v^\mu$ is a contravariant tensor of rank 1 then shouldn't force be a mixed tensor of type (1,1)?

The covariant derivative of a (1,0) tensor is a mixed tensor (1,1) but this doesn't seem to be the case. Force is always regarded as a rank 1 tensor. The derivative of velocity is acceleration. I'm ...
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How to calculate $\nabla\cdot (|L_{\perp}| \vec{v})$?

Let's assume I know $\nabla\cdot (|L_{x}| \vec{v})$ and $\nabla\cdot (|L_{y}| \vec{v})$, where $\vec{v}$ is the velocity field and $L_x$ and $L_y$ represent classical angular momentum components in $\...
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Where does the relative velocity composition law equation come from?

I'm trying to understand this paper (equation $2.8$ specifically): Bini, D., Carini, P., & Jantzen, R. T. ($1995$). Relative observer kinematics in general relativity. Classical and Quantum ...
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Understanding where equation $2.3$ comes from?

I'm trying to understand this paper (equation $2.3$ specifically): Bini, D., Carini, P., & Jantzen, R. T. ($1995$). Relative observer kinematics in general relativity. Classical and Quantum ...
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Does equations of motion work for distance and speed? [closed]

In some books,when solving to find the distance and speed of the object having motion in straight line,the three equation of motion are used.so my question is whether these equation of motion (i.e $v=...
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What does divergence of scalar times vector vector field physically mean?

We know that: $\nabla \cdot (f \vec{A}) = f \nabla \cdot \vec{A} + \vec{A}\cdot(\nabla f)$ Now divergence of any vector field can be understood in terms of whether the concerning flux is outgoing ($\...
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Can we interpret timelike, rest frame motion as velocity in the time direction? If so, does it cause charge to generate a ''$B$ field'' perp. to time?

For background: I've had courses on SR/GR from Hartle, E&M from Griffiths/Purcell, and know E/B fields are unified/transform with lorentz boost. My question is less about 'does SR account for E/B ...
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Intuition behind space-average velocity

Time-average velocity is easy to visualize. But I am struggling with the concept of space-average velocity. I know the formula and definition for these two measures: Space-average velocity = $ \frac {\...
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What does $\dot x$ mean as an operator in quantum mechanics?

I've been looking at a paper titled "Feynman's proof of the Maxwell Equations" by Freeman Dyson (American Journal of Physics 58, 209 (1990); https://doi.org/10.1119/1.16188) and I'm confused ...
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How to calculate average velocity in a time interval when it is exponentially changing?

For velocity that is changing linearly (like with constant acceleration) it quit easy, (end velocity - start velocity) / 2.0. But what if it is changing by exponential equation, for example v(t,d) = (...
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How to calculate traveled distance with non constant acceleration in time?

I know this formula D = vt + 1/2at^2* for calculating the distance given initial velocity, time and acceleration. But what if my acceleration is not static, but increasing exponentially defined by f(n)...
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Determine velocity vector on sloped surface

A golf ball is launched at a speed v and launch angle, β . At some point the ball is located on the rim of a hole. The view from above looks as follows: Vector v can be expressed in two components, ...
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Conflicting result for velocity and radius in physiology

My problem is that we say V = Q/A (V velocity, Q flow, and A area of pipe) in haemodynamics. Based on this formula, the velocity ​​is inversely related to the second power of the radius. Combining ...
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Angular velocity at a general point

I have been reading circular motion for a while and the magnitude of angular velocity is defined as component of linear velocity (perpendicular to the position vector) divided by position vector. But ...
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How important is the concept of rapidity in relativity?

After studying the concept of rapidity and the associated formulation of special relativity in terms of hyperbolic trigonometric functions of rapidity, I've come to understand the elegance of this ...
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Is e (COR) defined for whole situation or just during collision

According to wikipedia $${\text{Coefficient of restitution }}(e)={\frac {\left|{\text{Relative velocity after collision}}\right|}{\left|{\text{Relative velocity before collision}}\right|}}$$ ...
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Would an object travel forever if thrown in space? [duplicate]

for example, let's say you have an object like a stone or pencil and it is thrown at a certain velocity in space (also pretend that there are no planets, stars, black holes, or any other things that ...
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What causes things to gain the speed of nearby gravitational sources?

While I’m aware that this probably has a really simple answer, I can’t figure it out. For example, humans, apples, but also things outside of earth like the ISS travel along with the earth, at the ...
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Is observing (superluminal) velocity independent of choice of coordinates for asymptotically flat spacetimes?

Alcubierre's warped metric in ($1+1$)D is typically given in the form of: $$ds^2 = -dt^2 + [dx-v(t)f(r) dt]^2 \ \ .$$ Then it is nicely discussed how manipulating: $$-dt^2 + [dx-v(t) f(r) \ dt]^2=0$$ ...
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Why does it represent change in velocity?

In the above image a particle goes with velocity $v_0$ at some direction and then in an another direction where its velocity is represented by $v$. Both are same in magnitude but their direction is ...
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When exactly does velocity increase or decrease on an acceleration time graph? [closed]

How does the acceleration time graph show if and object is speeding up or slowing down? Is it possible to find the answer without any deep calculations? If yes then how? Like how can I find the ...
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Is there anything like negative deceleration?

I kinda understand acceleration, deceleration and negative acceleration but does anything like negative deceleration exist?
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Parabolic flow of fluid inside tube

I came across a fact on web that when a fluid flows through a cylinder the shape of its flow is parabolic. But according to me if we have a steady state then the velocity each of the concentric fluid ...
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Getting acceleration in one point of a solid knowing the acceleration of another point and the rotation of the solid

Consider knowing the rotation and the acceleration of a solid S1 at point A using an inertial sensor. The inertial sensor has its own system of axis R1. Is it possible to get the acceleration of an ...
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Does Heisenberg's uncertainty principle also apply to measuring velocity? Can we measure velocity at an exact time and point?

There will always be an error in measuring velocity because it is average velocity in some range of time not the exact time. So the physical quantity velocity doesn't exist at a moment. So how come ...
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Understanding the meaning of the two below expressions related to rate change [duplicate]

We know that velocity vector $\vec{v}$ is given by $\frac{d\vec{r}}{dt}$ where $\vec{r}$ is the position vector of a particle carrying a 2D motion . I would like to know what then $\frac{d|\vec{r}|}{...

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