Questions tagged [velocity]
The time rate of change of the position of an object
1,351
questions
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1answer
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2 objects moving towards a midpoint near light speed [on hold]
I have the following diagram (velocities are relative to p2):
and I have the following line of reasoning:
The speed of P2 relative to P1 is also 0.9c
Therefore P1 experiences 2 seconds of time ...
2
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0answers
43 views
Oil droplet in Electric field [on hold]
suppose a horizontal plate capacitor. They are separated by $d=0.005 \text{m}$. In a homogeneous field, the oil droplet ($m=3\cdot 10^{-15} \text{ kg}$) sits at the bottom of the lower plate. Like a ...
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14 views
Acceleration of a satellite orbiting Mars
I am studying how a satellite would move in orbit around Mars. I have calculated the velocity of its movement. However, if the gravity of Mars is the only force affecting the movement of the satellite,...
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0answers
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How to find the ideal intersection between constant object and controllable object?
So I'm an engineer who's a bit out of practice, but have taken up a side project for entertainment purposes. I'm trying to teach myself to code and find myself struggling to come up with a solution ...
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0answers
36 views
How to derive the group velocity in a dispersive medium and how to interpret it in momentum space?
:)
I had this homework where I was supposed to derive the group velocity of a given wave packet
$$\psi (x,t) = \frac{1}{\sqrt{2\pi}}\int_{-\infty }^{\infty}dk g(k)e^{i(\omega t-kx)}$$
where $$g(k)=e^{-...
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How do you determine whether answer is A or D? [on hold]
How do you tell the difference between graphs A/D from t=0 to their maximum postions given this eqaution.
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18 views
Group velocity of two cosines
I just encountered the following problem, which is really strange to me. I simply want to calculate the group velocity of the following wave
$$F(x,t) = \cos(k_1x) + \cos(k_2x-w_2t).$$
Now I thought, ...
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24 views
Adding Reference Frames Velocities to Create Acceleration
The earth’s rotational velocity at the equator is about 0.5km/sec. It’s orbital velocity around the sun is roughly 30km/sec. Over the course of a 24 hour period earth’s rotational velocity adds to or ...
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3answers
172 views
Proof that $v=\frac{dE}{dp}$ at relativistic speeds?
This is a formula I have seen stated in two different places in a relativistic context, but I do not know the proof and seem unable to derive it on my own. $E$ is the energy of a free particle, $v$ is ...
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16 views
Whether this calculation is applicable to impact application..?
I have some confusion with this calculation for my design.
I need to do the endurance testing for the pin which has to be loaded on flat face with the spring impact force, In this case how can I ...
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Minimum Speed for Supercavitation
In the various articles on supercavitation, naturally attention seems to be focused on how high a speed is achieved by a given device at its maximum. However, I would like to know how can on estimate ...
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1answer
30 views
Calculating Acceleration To a Predetermined Point [closed]
I've been struggling to find a solid solution for a problem I'm having.
I have an object in 2D space moving at some initial velocity, from some initial point to some final point, over a determined ...
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24 views
Transferring Kinetic Energy - a worldbuilding physics question
I'm working on an RPG for some friends and I'm curious about a magic system I'm thinking of designing and how it would interact with physics. Please bear with me as I'm neither mathsy nor a physicist. ...
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1answer
57 views
How does relative motion theory adjust other variables than kinematics' basics like velocity or displacement?
I have been confused on this concept for a while - suppose a boy is going from east towards west with some velocity on a bicycle and rain is falling in a vertical downwards direction.
Then, if we ...
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2answers
58 views
${}$ Kinematics: One dimensional motion [closed]
Above is the speed-time graph of a particle in motion along a constant positive direction, as per my textbook accelration in the interval 3 is positive. But I think acceleration in the interval 3 is ...
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2answers
61 views
Acceleration of a Bouncing ball when it hits the ground
The conceptual problem I am having difficulty with is something like this:
If a bouncy ball is dropped from some height $h$ and rebounds to a height of $0.75h$ in some time $t$ (for example), what ...
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2answers
100 views
Velocity of a ball rebounding off a moving train
At the bottom of this page says (my emphasis):
It's interesting to note the speeds in the cartoon. The
propeller-beanie kid sees his tennis ball moving away from him at 30
miles per hour. So ...
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2answers
54 views
Kinematics: One dimensional motion
If a particle is moving in one dimension with constant speed, can we say acceleration is zero at all the points?
Answer given in my textbook is yes acceleration is zero.
But I think it can undergo a ...
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5answers
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Why do these two ways of understanding constant acceleration give different results?
I have a question pertaining to the concept of acceleration and it's formula - Both seem to give me different answers.
I was asked:
A train is moving at a velocity of $20\ \mathrm{m/s}$. It hits ...
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0answers
69 views
Converting velocity vector formula from Cartesian coordinate system to polar coordinate system
I have a little question about converting Velocity formula that is derived as,
$$\vec{V}=\frac{d\vec{r}}{dt}=\frac{dx}{dt}\hat{x}+\frac{dy}{dt}\hat{y}+\frac{dz}{dt}\hat{z}$$
in Cartesian Coordinate ...
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2answers
59 views
Intuitive explanation to why force perpendicular to velocity results in circular path
I know in circular motion F is perpendicular to V. But I don't understand how this results in a change in direction and no change in speed ( which ultimately results in a circular path).
In short, ...
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1answer
36 views
Meaning of normal acceleration?
acceleration means the rate of change in velocity (vector quantity) and the differentiation means to divide a certain quantity into small elements (i.e $dx$) as we do to find the acceleration at any ...
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1answer
13 views
How would one represent/model the effect of air resistance on horizontal motion? [duplicate]
Evidently, there are formulas that allow us to represent the effect of air resistance on the velocity of an object in free fall but how would one calculate the effect of air resistance on horizontal ...
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4answers
106 views
Why the need for defining the velocity as a derivative? [closed]
Something intuitive and fundamental as the concept of velocity (of a particle for example) in classical physics is defined as a derivative, a concept to me quite vague and strange, although i know its ...
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3answers
73 views
Does Einstein velocity addition rule work only for speeds, or for velocity vectors as well?
Einstein's Velocity addition rule (https://en.wikipedia.org/wiki/Velocity-addition_formula#Special_relativity) was used to describe to replace galileo's in account for relativity.
However, in many ...
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1answer
61 views
Understanding Average Velocity's Logic
Firstly, I'm a new learner of physics. I'm a bit confused about average Velocity's logic. There is a problem that I am trying to solve as the following :
You walk $73.2$ m at a speed of $1.22$ m/s ...
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1answer
54 views
Does friction depend on velocity?
I wanted to ask why (how) friction on wet surfaces and friction on dry surfaces have different velocity dependence?
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2answers
39 views
Need of describing the term acceleration [duplicate]
What is the need of acceleration when we have velocity
As I think velocity as 1m/s means 1m covered in 1s and 1m/s^2 means 1m covered in 1s per 1s this statement creates confusion when it comes to ...
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2answers
56 views
What is the need of acceleration? [closed]
As we can usually predict the various forces that a body might be undergoing based on its position and its velocity.Hence what is the need of acceleration?
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1answer
31 views
Why are you accelerating yet remaining at a constant speed while going around a curve? [duplicate]
We have to write a rap in physics, and it has to answer a prompt he gave us on this packet. The prompt for the verse I am writing is:
Pretend you are driving a car on the freeway going 65 mph. The ...
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1answer
63 views
Particles approach each other with .8c [closed]
Two particles travelling with velocity .8c (observed from ground frame) each approach each other.
What is their relative velocity wrt ground frame.
According to me they should be added.
I am very much ...
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2answers
68 views
Why is relativistic velocity addition not symmetric?
The Galilean velocity addition formula is $$u' = v + u$$ This is symmetric if one swaps $v$ and $u$.
What are the fundamental reasons why the (generalized) relativistic velocity addition formula is ...
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2answers
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How does instantaneous velocity or acceleration have any other numerical value than 0? [duplicate]
Instantaneous velocity is defined as the limit of average velocity as the time interval ∆t becomes infinitesimally small. Average velocity is defined as the change in position divided by the time ...
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2answers
53 views
Area under a velocity graph
If I took the definite integral of a velocity graph from 0 to 10 seconds, the answer would be the change in position over those 10 seconds correct? I am told by my teacher the area is change in ...
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1answer
53 views
Motion of a body falling in resistive medium [closed]
Obtain the equation of motion for a particle falling freely under the action of gravity under a resistance which is directly proportional to the square root of velocity. Describe the motion and find ...
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3answers
44 views
Will there be any radial velocity in absence of centripetal force and angular acceleration?
In the question it is stated that there is a ring which can move along a smooth rod. The rod itself is rotating in a horizontal plane with one fixed end with uniform angular velocity. Initially the ...
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6answers
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Question about derivation of kinematics equations
Apologies if this has been asked before, but I browsed the sub and couldn't find something specific.
I understand the derivation for one of the equations as follows:
\begin{gather}
\frac{dv}{dt} = a ...
0
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0answers
48 views
Why are velocity and kinetic energy not proportional? [duplicate]
In the equation $E_k=\frac12mv^2$ the fact that the kinetic energy of a moving object is not proportional to it's velocity seems counter-intuitive to me.
Put another way, it seems intuitive to me ...
0
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1answer
56 views
Kinetic energy in Lagragian mechanics [duplicate]
In my classical mechanics class they asked why the kinetic energy for an holonomic mechanical system has the homogeneous quadratic form.
Of course for a autonomous standard system( system that is ...
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2answers
44 views
What is the use of Subtracting velocity?
By adding two velocity's direction we get the direction the object has travelled. But what do we get when we subtract vectors?
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0answers
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 ...
1
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3answers
101 views
Why do we need concept of average velocity and average speed? [closed]
As I was thinking about average speed / velocity, I got curious, why do we need this concept. This average speed / velocity doesn't give accurate information about motion of an object then why it is ...
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4answers
118 views
Why was the concept of velocity created? [closed]
Why do we use velocity instead of speed for different physics problems?
I recognize how they are different but why use one over the other?
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1answer
36 views
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.$$
However, I was reading https://arxiv.org/abs/1305....
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2answers
74 views
If acceleration $a = v\cdot\frac{\mathrm dv}{\mathrm dx}$ , then why isn't acceleration always zero when velocity is zero? [duplicate]
We know that,
$$\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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0answers
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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 ...
2
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5answers
136 views
Calculating mean velocity: using time or velocity? [closed]
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 ...
2
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3answers
115 views
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 ...
6
votes
2answers
230 views
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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2answers
111 views
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 "...
