Questions tagged [velocity]

The time rate of change of the position of an object

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38 views

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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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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19 views

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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135 views

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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1answer
36 views

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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179 views

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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23 views

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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230 views

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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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
93 views

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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93 views

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 $\...
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Why the velocity $v$ is taken as value and not as definition in special relativity equations?

Why the velocity $v$ is taken as a value and the definition of velocity not applied on a relativistic equations? The equations of time dilation and length contractions as we know are $$L = {L_0}{\...
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28 views

Braking power and kinetic energy

I am currently stuck at a part of a problem i set myself. I am trying to create an equation for the stopping distance with respect to the force applied to the braking pads. I currently have two ...
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1answer
143 views

instantaneous velocity center

The instant center of rotation, also called the instantaneous velocity center is the point fixed to a body undergoing planar movement that has zero velocity at a particular instant of time. For ...
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Can I calculate force in the following situation if the following information are given?

A moving car collides with a stationary car, after which they move at the same velocity. After going some distance they stop. The following information is given: mass of the 2 cars the velocity of ...
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Is the velocity of a string that is being rotated around a central point the same at any point on the string?

Say that you have a weight attached to a 2 metre long string, and you are rotating the weight at 5 m/s. Is every point on the string going to be rotating at that same velocity of 5 m/s, or is the ...
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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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How to understand the process of the kinetic energy formula? [duplicate]

$$\frac{1}{2} mv^2 = K.E.$$ What is the purpose of $v^2$; why can't use $v$ instead? Why this question is arising because of that I learned the whole process of speed= distance/time. (I know How it ...
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Why a Box moving at Constant Velocity isn't doing Work?

This was a question from an A-Level past paper and the question is pretty straightforward. I was in a hurry so I couldn't think much on this problem and chose $C$ as my answer, checked it on the ...
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If absolute velocity does not exist, how can we say a rocket accelerates in empty space?

If a rocket in space fires its thrusters, it is propelled forwards as per the laws of motion. This can be measured by its position relative to other bodies in the universe. Hypothetically if there ...
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1answer
195 views

Reconciling $Q=PR$ and $Q=vA$

Say we have a closed loop system, where the flow $Q$ is constant through a pipe. Then, at one segment of the pipe, we make the radius smaller. This causes the resistance $R$ to be greater, so the ...
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1answer
34 views

Time taken to reach common velocity - collision

Say for instance I have two objects with different masses that collide in-elastically the resulting velocity will be $ v =\frac{m_1 v_1 + m_2 v_2}{m_1 + m_2}$. What I don't fully grasp is how to ...
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168 views

How can we find velocity, acceleration etc, of a revolving particle with respect to an observer inside the circle(not at center)

A particle is revolving in horizontal a circle of radius $R$ with constant speed of $|\vec{v}|$ and constant angular velocity $\omega$. There is another observer standing inside the circle, at a ...
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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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The instant an accelerating object has zero speed, is it speeding up, slowing down, or neither?

This problem is from Khan Academy. Specifically for the blue point circled in red, the answer is that at this blue point, the object is neither speeding up nor slowing down. When I think about the ...
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226 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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Relativistic mass effect

Does relativistic mass phenomena only appear while accelerating or even when the object is travelling at constant velocity (say 90% speed of light)?
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Meaning of the term speed of light in context of an object of non-zero mass

We know from GR that an object of non-zero mass cannot propagate at light. I have a problem with the term speed of light. Does it mean the relative speed of that object with another object or frame of ...
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1answer
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What determines the speed of waves in water?

While I was walking my dog this morning, I passed over a canal filled with boats, barges, and kayaks all of different masses and moving at different speeds. I noticed that all of these vessels left ...
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Intuition of Distance covered when accelerating [duplicate]

When you're moving at $5$ m/s for $1$ second, you have traveled $5$ m. When you're moving at $5$ m/s (initial velocity) and you accelerate $2$ m/s for $1$ second, you have traveled $5$ m + $1$ m (...
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Gravitational “acceleration” and frequency change of a photon?

For massive particles, force translates into acceleration which again is a change of the velocity vector in direction and/or magnitude. For a photon, the velocity magnitude cannot change, only the ...
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5answers
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Intuition of 2D Velocity Vectors [duplicate]

I understand 2D vectors in terms of displacement. For example, Bob moves 3m to the east and 4m to the north, the total change in position (displacement) equals 5m to the north east. But I don't ...
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1answer
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Motion Along a Straight Line: Calculate velocity of a stream

A swimmers speed along the river is 20 km/h and upstream is 8 km/h. Calculate the velocity of the stream and the swimmers possible speed in still water. I understand what the variables are and I ...
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1answer
87 views

High velocity mushrooms?

So y’all know meteoroites burn up in our atmosphere I’m looking for an equation or something that will allow me to calculate how fast a substance can move before it starts to burn up. Specifically I’m ...
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1answer
50 views

How to know is four-velocity is directed towards future or towards past?

Consider a four-velocity vector $\mathrm{u}=(u^0,u^1,u^2,u^3)$. The zeroth component of position is $x^0=ct$. How do I know if $\mathrm{u}$ is directed towards the future or towards the past? Is it ...
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63 views

Maximum Vertical Velocity of Pendulum

Say there is a 10N pendulum held parallel to the ground. In a frictionless environment, it will continue swinging along a semicircular path. The pendulum tip should have the highest horizontal ...
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2answers
4k views

Derivation of the average Velocity formula with constant acceleration (using calculus)

I have been looking at $$ v_{avg} = \frac{v_{i} + v_{f}}{2}, $$ when the acceleration is constant, where $v_i$ is equal to the initial velocity and $v_f$ is equal to the final velocity. How can ...
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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 ...