Questions tagged [velocity]

The time rate of change of the position of an object

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Speed of the Earth through universe [on hold]

If two negatively charged spheres repel each other in the same way indipendently of Earth velocity does the movement of the Earth around the Sun which is at a short moment in direction with the Milky ...
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A Second Geodesic Equation?

I have a question about the geodesic equations. I understand the following formulation of it: $$\frac{d p^\mu}{d\tau} = - \Gamma^j_{v\mu}p^vp^\mu.$$ However, I was reading https://arxiv.org/abs/1305....
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If acceleration $a = v\cdot\frac{\mathrm dv}{\mathrm dx}$ , then why isn't acceleration always zero when velocity is zero? [duplicate]

We know that, $$\begin{align} a&=\frac{\mathrm dv}{\mathrm dt}\\[3pt] &=\frac{\mathrm dv}{\mathrm dx}\cdot\frac{\mathrm dx}{\mathrm dt}\\[3pt] &=v\cdot~\frac{\mathrm dv}{\mathrm dx} \end{...
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Calculating mean velocity: using time or velocity?

Background I have been running tests which involve timing an object moving a certain (fixed) distance, $s$. Each test has been repeated 3 times, and the 3 times ($t{_{1}}, t{_{2}}, t{_{3}}$) for the ...
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Explanation that air drag is proportional to speed or square speed?

A falling object with no initial velocity with mass $m$ is influenced by a gravitational force $g$ and the drag (air resistance) which is proportional to the object's speed. By Newton´s laws this can ...
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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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How can velocity be measured on a persons hand?

How can Velocity of a hand be measured for example i have my hand flat bent backward like holding a tray, i want to measure the initial speed of my hand as motion begins when i flick my hand
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A car covers 110 meters in 10 seconds then covers 140 meters in next 10 seconds.The acceleration is constant.Whats initial speed and acceleration [closed]

The car moves in a straight line. I have tried using distance, time, and speed graph but my teacher says it is wrong.
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Is Velocity Really a Vector?

In non-relativistic physics, physical quantities $Q$ are characterized by how they transform under a Galilean transformation $g \in \mathcal{G}$. $$ Q \rightarrow Q' = D[g]Q$$ where $D[g]$ is the ...
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Can the flow be irrotational if the viscous forces act on fluid?

I tried to answer the question only using the definitions and the Navier-Stokes equation: $$\rho \frac{Dv}{Dt} = -\nabla P +\rho g -\mu[\nabla \times(\nabla \times v)] $$ In my opinion if the ...
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Understanding terms Twist and Wrench

In kinematics, physics and especially robotics, we often encounter the terms Twist and Wrench. Twist is (LinearVelocity, AngularVelocity) and Wrench is (Force, Torque). The reason I'm confused is I ...
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What does it mean to velocity be a derivative of position? Isn't position a point, not a function? [closed]

So in mass-spring simulation I encountered that one simulates particles by using positions and velocities of particles etc. By mechanics: Velocity is the derivative of position. But, isn't "...
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If I want to spin a disc or rod with an objective of high tip/edge velocity (of .1c) what are my limitations?

What are our limitations on being able to spin a disc or rod to create a relativistically fast tip/edge speed? My thoughts are you should be able to increase the radius of the spinning object to ...
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Maximum acceleration on a turn

The question $\\$ Suppose a car enters a turn with an initial speed $\vec{v_1}$, and comes out with a final speed $\vec{v_2}$ perpendicular to the direction of $\vec{v_1}$. The driver does everything ...
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Alternative definition for Lorentz factor?

I have never encountered this before (encountered it now in Sean Carroll's GR text when discussing the benefit of solving problems in locally inertial references frame). Let $\gamma$ be the Lorentz ...
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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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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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How do you correctly apply $a=v\cdot\text dv/\text ds$? [closed]

I know that $a=v\cdot\text dv/\text ds$ can be deduced by simple algebra and calculus and is correct. But once I was analyzing the motion of a ball projected straight up in free gravity. If I apply $...
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Relative motion between two particles

I already know the relation of relative velocity as : Vab=Va-Vb So is there any derivation for this relation or is just how it is defined? Relating to this i am finding some hard time to imagine why ...
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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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Does horizontal inertia affect the time it takes something to reach the ground?

I am new to physics. I’m confused about how an bullet shot horizontally would land at the same time with as a bullet dropped vertically (ignoring air resistance and the curvature of Earth). Having ...
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Relative motion with relativity [closed]

In an inertial frame of reference (let's say a car moving with certain constant velocity in which I am sitting) If I observe the motion of another car through my frame of reference i.e.car, will I be ...
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If we say “an object is at rest,” can we also say “the object is moving at a constant velocity?” [closed]

If we say "an object is at rest," can we also say "the object is moving at a constant velocity?" Of course, the constant velocity would be zero, so it's mathematically sound. However, the wording ...
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How to get the four-velocity components from a given metric tensor?

I’m a little bit confused about how to get the four-velocity components from a given metric tensor (or line element). For instance, which are the components of the four-velocity in the Schwarzschild ...
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Can one construct a covariant velocity from the contravariant one using the metric tensor in plane polar coordinate system?

In plane polar coordinate we know $ds^2=dr^2+r^2d\theta^2$ from which we can write the components of the covariant metric tensor $g_{11}=1$, $g_{22}=r^2$, $g_{12}=g_{21}=0$. Upto this point I ...
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Does throwing a penny at a train stop the train?

If I stand in front of a train and throw a penny at it, the penny will bounce back at me. For the penny to reverse its direction, at some point its velocity must go to zero. This is the point it hits ...
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What is the difference between uniform velocity and constant velocity? [closed]

I think that uniform velocity implies constant speed but not constant direction. while constant velocity implies constant speed without any changes in direction. Both tell us that there's no ...
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A doubt regarding Modelling physical phenomena and position uncertainty

For example, in velocity, when we say $v=\frac{dx}{dt}$, there is no proof for it. Its almost like an axiom. Something taken to be true, without a proof. How do I know that for every $x=f(t)$, $v=f'(t)...
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Relative velocities problem ; how to draw useful diagrams if more than 2 things are changing?

Two students are canoeing on a river. While heading upstream, they accidentally drop an empty bottle overboard. They then continue paddling for 1.9 h , reaching a point 1.2 km farther upstream. At ...
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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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How do I calculate how strong of a field I need to repel a proton in a span of time

How do I calculate how strong of a field I need to repel a single proton in a given span of time, given that I know it's velocity.
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Why does kinetic energy below molecule bond energy break bonds?

I was thinking about why bullet can break molecular bonds when it hits solid target despite the fact that the kinetic energy of the individual atoms that make up the bullet is less that the molecule ...
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What is the speed of air molecule?

Given the minimal temperature measured in the Earth's atmosphere is not $0\space K$, air molecules are moving. I see no reason for air molecule to move all at the same speed. The question is ...
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Velocity field to a permeability field using poisson pressure equation

I have a velocity field and I want to get a pressure field. In my experiment we're controlling the pressure at the inlet and the outlet. I have Dirichlet boundary conditions at the inlet and outlet ...
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Wavelength of a particle [duplicate]

As we know wavelength of a particle is equal to (Planck's constant / momentum), so here momentum $= mv$ where $m$ is a mass of an object and $v$ is the velocity of an object. What will happen when ...
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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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WHY did physicist defined velocity as displacement divided by time, why not displacement * time? [closed]

V=S/T. As per my knowledge i think ratio as division and it don't give any meaning like this much displacement in this much time. So i think physicists only used division as notion for velocity. But ...
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Application of Bernoulli's equation to siphon

I'm trying to understand how to use Bernoulli's equation in practice. So I will make an example of where is my confusion. I found this great explanation on Wikipedia about the siphon, but there is a ...
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Pressure in the pipe when the pool is draining out

I have a question: the situation is as follows: There is an open pool (in blue) to which a pipe is connected. The pressure above the pool is equal to the air pressure = 1 bar. In normal configuration ...
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Is it possible to find $\mathbf{v}$ explicitly when $\mathbf{F}$ varies with $\mathbf{v}$?

I have the following problem (NO, this is not to ask for a solution to this problem). A block is placed on a plane inclined at an angle $\theta$. The coefficient of friction between the block and ...
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Calculating velocity of electrons in a vacuum tube (read description)

If I use a high voltage DC current in a vacuum tube to bring a lower power AC current into a vacuum tube, how do I calculate the average velocity of the AC electrons?
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Velocity-Dependent Potential and Helmholtz Identities

I'm currently working through the book Heisenberg's Quantum Mechanics (Razavy, 2010), and am reading the chapter on classical mechanics. I'm interested in part of their derivative of a generalized ...
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1answer
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Force on a particle with uniform velocity

Let's say a particle is moving in a straight with no acceleration in an inertial frame. By Newton's laws we know that the force acting on it must be 0. But my question is, why doesn't uniform velocity ...
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Do orbiting masses accelerate or decelerate (relative to us) near black holes? [duplicate]

Apologies if this question seems stupid; I was just curious after watching a documentary, and I am not a trained astrophysicist. Simply put, I cannot reconcile the (perhaps misunderstood) facts that ...
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Constant Acceleration and Displacement

How can I conduct an experiment to show that the area under a velocity-time graph equals the displacement when the velocity is changing at a constant rate? I've tried to measure free falling objects, ...
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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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How to calculate velocity from the attraction of two charges?

I need to calculate the acceleration of an proton to a metal plate with a charge of 16 Coulombs (negative charge), 1 meter away. Then I need to calculate the velocity at the moment it passes the plate....
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1answer
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Partial Integration and the Levi-Civita Symbol

I'm currently working through the book Heisenberg's Quantum Mechanics (Razavy, 2010), and am reading the chapter on classical mechanics. I'm interested in part of their derivative of a generalized ...
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2answers
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How can I understand if an object stay (zero velocity) or moving with constant velocity (zero acceleration)

I thought a scenario like; lets say I am looking an object and there is nothing except this object. Is there a way to understand that if this object is stay on its position or if object moving with a ...
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1answer
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Is four velocity always given by $U^{\mu} = d x^{\mu}/d\tau$?

I was taught that four-velocity is defined as $${\bf U} = \frac{d \bf x}{d\tau}$$ and that it has the components $$U^{\mu} = \frac{d x^{\mu}}{d\tau}$$ where $d\bf x$ is the four displacement and $\...