Questions tagged [velocity]
The time rate of change of the position of an object
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What would qualify as a deceleration rather than an acceleration if speed is unchanged?
The instantaneous acceleration $\textbf{a}(t)$ of a particle is defined as the rate of change of its instantaneous velocity $\textbf{v}(t)$: $$\textbf{a}(t)=\frac{\mathrm{d}}{\mathrm{d}t}\textbf{v}(t)....
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If starting speed is faster than terminal velocity then what?
If an object is say thrown down (vertically) at an initial speed that is faster than its terminal velocity, what would happen to that objects speed? Would it slow down?
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From how high could have Felix Baumgartner jumped without disintegrating like a shooting star?
Today Felix Baumgartner jumped from 39 kilometres high and reached the earth safely.
Just considering friction, from how high can a human jump?
I expect that from a certain height, he would have ...
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Integrating acceleration - wrong choice of bounds in textbooks?
I've noticed in my physics textbook (and in a lot of other popular sources), that the process of integrating non-constant acceleration to get to a velocity formula, the integrating bounds imposed on ...
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Is the velocity with which molecules of the medium oscillate same as velocity of the sound in that medium?
I wanted to know that under sound field applied molecules of the medium oscillate with some velocity in the direction of sound propagation. Is this velocity same as velocity of the sound in that ...
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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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Calculate speed from accelerometer
I am trying to use my accelerometer on my mobile device (smart watch to be specific) to calculate a persons arm swing speed.
The data returned from the accelerometer is in $m/s^2$.
Since the ...
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Definition of four-velocity: why define it with proper time of the object?
The four-velocity(world-velocty) is defined by : $u^μ=\frac{dx^μ}{dτ}$ ,where $τ$ is the proper time of the object.
I don't understand why it's defined with respect to the proper time but not the time ...
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When the direction of a movement changes, is the object at rest at some time?
The question I asked was disputed amongst XVIIe century physicists (at least before the invention of calculus).
Reference: Spinoza, Principles of Descartes' philosophy ( Part II: Descartes' Physics, ...
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Velocity in a turning reference frame
I often see the relation that $\vec v=\vec v_0+ \vec \omega \times \vec r$ in a turning reference frame, but where does it actually come from and how do I arrive at the acceleration being $$\vec a=\...
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Does a moving object curve space-time as its velocity increases?
We always hear how gravity bends space-time; why shouldn't velocity?
Consider a spaceship traveling through space at a reasonable fraction of the speed of light. If this spaceship, according to ...
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What is the terminal velocity of a sheep?
Inspired by this question on Gaming.SE
Using actual in-real-life physics, what would the terminal velocity of a sheep actually be? I would assume it would be around 50m/s, but I might be wrong.
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Why are some energies dependent on reference frame, and some are not? And why is transfer between them possible?
For example the chemical energy of a kilogram of gasoline is 44-46 MJ/kg. It is only dependent on its chemical structure, which stays the same, whether the gas tank moves or stays still relative to ...
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Is velocity real?
This sounds like a stupid question but I am do not grasp physics concepts easily. "Velocity" is just the change in displacement over the change in time. I can see displacement and time as ...
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What is the terminal velocity for a mobile phone
You may have seen the story of the iPhone which was dropped from perhaps 13,500 feet by a skydiver - it survived.
This made me wonder how to work out the terminal velocity for something like that. ...
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Can you completely explain acceleration to me?
I understand what acceleration is, and I know the formula, and I understand it's a vector.
I just don't understand how the equation works exactly. I'm kind of picky, I know, but bear with me.
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What is the instant velocity? [duplicate]
The velocity is the variation rate of the position correct? So does it make sense to talk about velocity without time?
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How can an object's instantaneous speed be zero and it's instantaneous acceleration be nonzero?
I'm studying for my upcoming physics course and ran across this concept - I'd love an explanation.
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Is velocity an angle?
I am not a physicist. I have only rudimentary notions about the following.
I looked for similar questions on SE but I did not find any. I also tried search engines but results relate to angular ...
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Why is average velocity the midpoint of initial and final velocity under constant acceleration?
Since average velocity is defined as$^1$
$$\vec{\mathbf v}_\mathrm{av}=\frac{\vec{\mathbf x}-\vec{\mathbf x}_0}{t-t_0},$$
where $\vec{\mathbf x}$ denotes position, why is this quantity equal to
$$\...
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How do we measure the velocity in curved space-time?
In almost general case, the space-time metrics looks like:
\begin{equation}
ds^2 = g_{00}(dx^0)^2 + 2g_{0i}dx^0dx^i + g_{ik}dx^idx^k,
\end{equation}
where $i,k = 1 \ldots 3$ - are spatial indeces.
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General relativity: For massless particles, is the momentum and velocity 4-vectors equal?
I am following Carroll's GR book. He explain that it is convention to parameterize geodesics of photons by a parameter $\lambda$ such that
$$p^\mu ~=~ \frac{d x^{\mu}}{d \lambda}.\tag{3.62}$$
But ...
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What is displacement? Position relative to a reference point or change of position
What is the "official" or most useful definition of displacement in the context of kinematics?
There are two common ones:
Displacement is the length and direction of a line from a fixed reference ...
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Angular velocity relative to different frames
In Goldstein it is said "It is intuitively obvious that the rotation angle of a rigid body displacement, as also the instantaneous angular velocity vector, is independent of the choice of origin of ...
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Do charged particles move along the electric field line?
I was discussing with my friend about electric field lines and he said that:
given a test charge at rest at a point in the region of the electric field the charge will continue to move along the path ...
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Why is the scalar product of four-velocity with itself -1?
My GR book Hartle says the scalar product of four-velocity with itself $-1$?
Consider the definition of four velocity $\mathbf{u} = \frac{dx^{\alpha}}{d\tau}$. Suppose I take the scalar product of ...
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What's the speed of light when viewed from the side?
Suppose a pulse of light is sent from $A$ to $B$ in a rigid triangle $ABC$. While the pulse is moving from $A$ to $B$, what is it's velocity relative to $C$?
The special character of the photon among ...
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Can we escape Earth's gravity slowly?
I had a recent conversation with my girlfriend, who is a physics grad student. She was kind enough to listen to me rant about an idea concerning escape velocity. Unfortunately, I am still thinking ...
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Can I find the acceleration or velocity when my displacement-time graph is discontinuous?
Today, I encountered the problem where I was asked to find the velocity and acceleration from displacement-time graph but the displacement-time graph was discontinuous. So I am unable to find the ...
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Is there an approximation for the Lorentz factor for very large velocities?
I am aware of the approximation generally used for low speeds to calculate the Lorentz factor, that being,
$$\gamma \approx 1 + \frac{1}{2} \left(\frac{v}{c} \right)^2$$
But I need the exact ...
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High speed does not kill. Does acceleration do it ? or jerk?
In a recent question the OP asked why high speed will not kill us.
The accepted answer, highly upvoted, stated very first that
Speed doesn't kill us, but acceleration does.
The second answer (...
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Can we measure the one-way speed of anything at all? [duplicate]
I know the one-way speed of light question has been exhausted, and I'm sorry for the naive question, but I would like to understand one thing. Can we measure the one-way speed of anything at all? If ...
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Is speed an intensive property?
I remember being taught in elementary physics that while it makes
sense to add volumes, masses, or heat, it makes no sense to add
temperatures.
As I wanted to use that to illustate some other issue, ...
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Terminal velocity of two equally shaped/sized objects with different masses?
I've tried doing research on this and there are some similar questions. However, they have slightly different scenarios and to make sure I understand things perfectly, I wanted to word it into my ...
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Why are coordinates and velocities sufficient to completely determine the state and determine the subsequent motion of a mechanical system?
I am a Physics undergraduate, so provide references with your responses.
Landau & Lifshitz write in page one of their mechanics textbook:
If all the co-ordinates and velocities are ...
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What is the difference between impulse and momentum?
What is the difference between impulse and momentum?
The question says it all...I know the second of of them is mass * velocity, but what is the first one for, and when is it used? Also, what are its ...
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Why does the mean speed of gas particles include $\pi$?
In chemistry we are learning about kinetic molecular theory (KMT) of gasses, and I just couldn't help being surprised when I saw $\pi$ in the equation of mean speed. I know that whenever $\pi$ is ...
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Why are position and velocity enough for prediction and acceleration is unnecessary?
In classical mechanics, if you take a snapshot and get the momentary positions and velocities of all particles in a system, you can derive all past and future paths of the particles. It doesn't seem ...
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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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What is the velocity in the Lorentz equation relative to when considering a vacuum?
The Lorentz Equation
$\mathbf{F}=q(\mathbf{E}+\mathbf{v} \times \mathbf{B})$
involves a velocity vector $\mathbf{v}$. What is this velocity relative to? Based on e.g. this resource, it seems that when ...
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Parallelogram law of vectors
[This is a very silly question. Will be a great help if someone could answer this question]
How is this law proven? I am not asking about the proof itself rather asking about the preliminary ...
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Why is rapidity additive?
With the rapidity $\phi$ defined so that $\frac{v}{c}=\tanh{\phi}$, say you have 3 parallel moving reference frames $S$, $S'$ and $S''$ with a constant but different velocity/rapidity.
If the ...
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What does squaring a vector mean?
So,in the 3rd equation of motion,i.e $v²=u²+2as$,what does the square on the final velocity and initial velocity actually mean?And how does it make an effect on their direction?
suppose upwards vector ...
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What is the relationship between rolling resistance and velocity?
I'm a games programmer, trying to write a simple car physics simulation. I'm aware that a car travelling in a straight line will exert a traction force that drives it forwards (by turning the wheels ...
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Is the four-velocity always normalized?
In the book i have reading defines the four-velocity like $$U^\mu=dx^\mu/d\tau.$$ The metric used is $\eta_{\mu\nu}=diag(-1,1,1,1)$. It is straightforward to show that the norm of the four-velocity is ...
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General Relativity: Why is the energy $E = - p_{\mu} U^{\mu}$?
This follows Carroll's Gravity book (page 110).
An observer with four-velocity $U^{\mu}$ (such that $g_{\mu\nu}U^{\mu}U^{\mu}=-1$) measures the energy of a particle along a geodesic $$p^{\mu} = \frac{...
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Why can't conservative forces depend on velocity?
In my mechanics lecture notes, it is written that, for a force $F$,
To be conservative, $F$ must be a function of position only: forces that depend on velocity, time, etc. cannot be conservative.
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Relative velocity greater than speed of light
Is it possible a relative velocity between 2 objects to be greater than the speed of light?
I know that it is impossible to reach the speed of light considering us to be immobile but is this ...
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Does Super Mario physics work in reality? [duplicate]
This illustration summarizes my question:
Please assume no air resistance (unless that makes a large difference). Here's what we concluded, but I could use both confirmation and also help with the ...
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Method of averaging velocities of electron when deriving drift velocity
Here is derivation of drift velocity.
Assume there is a field $\vec{E}$ inside the conductor(wire).
Using equations of motion we can say that for every charge inside the conductor, $$\vec{v_1}=\vec{...