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Questions tagged [velocity]

The time rate of change of the position of an object

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Parabolic Motion: finding velocity and angle [on hold]

I have been stuck at this problem for the last couple hours: A ball is trown at a wall distant d=7m and it hits at an heighth h=3m. The ball reaches the wall in t=1.25s. What is the in inital ...
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1answer
49 views

What is the interpretation of speed of a travelling wave, based on $\frac {\partial x}{\partial t}$ formula

Motion satisfies the wave equation if the following holds true $$\nu^2 * \frac {\partial ^2 \psi} {\partial x^2} = \frac {\partial ^2\psi} {\partial t^2}$$ where $\psi$ is the vertical displacement ...
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1answer
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What if a spaceship going half the speed of light turned on its headlights in both directions?

If the spaceship, travelling at c/2 were to turn on only its forward facing headlights, then after one second (relative to us, the stationary external observers) we would see that the ship has moved ...
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How do I calculate the velocity (after the collision) of a pinball colliding with moving flippers

I am working on a pinball game implementing all of the physics myself. I'd like to know how I would calculate the balls velocity after a collision with moving flippers. We are assuming there is no ...
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Horizontal and Vertical Velocity of point on arbitrary wave profile $\eta = \eta(x,t)$

Say I have for any position $x$ and any time $t$ that I want I know what is the height $\eta$ of an arbitrary wave so that I basically have the function $\eta = \eta(x,t)$ that describes the free ...
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14answers
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Why doesn't a braking car move backwards?

The net force on an object is equal to the mass times the acceleration, $F = ma$ When I brake on a (moving) car, the net force is negative, therefore causing the resulting acceleration to also be ...
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2answers
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Question about derivation of four-velocity vector

In order to describe a notion of rate of change of positon, in four-dimensional spacetime, we have to introduce the concept of four-velocity. So, consider the following: For a massive particle ...
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1answer
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Calculating the final velocity of a simple electric train, cont [closed]

So I have a school project that I am doing which is basically calculating the final velocity of a simple electric train (aka the battery). I am in grade 12. https://www.youtube.com/watch?v=J9b0J29OzAU ...
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3answers
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What would be the minimum velocity of a particle performing S.H.M.?

We were asked a simple question on a test: What is the maximum and minimum velocity of a particle performing an SHM? Note here that we're talking about a generic standard SHM here. If the maximum ...
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1answer
32 views

What's the velocity for a person falling from a building?

I saw that in the neighborhood a person fell our of 25th floor down the street (ground floor). I was intrigued by some questions about such situation, but all of them are out of one question: What's ...
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1answer
24 views

Are my observations about the differences between average velocity and speed, in 1 dimension, correct?

I've been struggling to understand the differences between average velocity and average speed in 1 dimension; by doing some exercises I think I have figured it out, but i want to check if I'm correct. ...
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If the speed of light is a limit, is there a way to tell which direction we are moving through space and how fast?

Say two photons start at point A, and go in opposite directions. They will be traveling apart at 2x the speed of light correct? So if this limit is how fast you are able to travel through space (and ...
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2answers
37 views

Can two electron moving in opposite direction move faster than light? [duplicate]

Suppose we are moving two electrons in opposite direction both having a speed of 1.6e8 meter per sec.When they will cross each other then their relative velocity will be 3.2e8 ms_1.Isn't it faster ...
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2answers
61 views

Speed of a falling object

When an object is dropped, does it accelerate to terminal velocity? or is it at terminal velocity immediately?
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1answer
34 views

Work done on box [closed]

I am having a hard time grasping this. W = Fd = mad, and given v vs t graph, the area under the curve will give us d. When the velocity graph draws a horizontal line, a=0. Thus I thought that A = C ...
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1answer
45 views

Types of Collisions and velocity

I know that there are three different collisions elastic, inelastic and perfectly inelastic. I wanted to know how the three velocities would rank respective to the type of collision. For example, if a ...
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1answer
31 views

Relation between strain and velocity

The strain tensor writes $\epsilon_{ij}=\frac{1}{2}\Big(\frac{\partial u_i}{\partial x_j}+\frac{\partial u_i}{\partial x_j}\Big)$ with $u_i$ the displacement in the $i$ direction. Then $\frac{\...
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2answers
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Confused with derivative and partial derivative

suppose $x=f(t)$ with a constant acceleration. Then does $\frac{\text d x}{\text d t} = \frac{\partial (x)}{\partial(t)}$ since the position in $x$ only changes with time? Then the acceleration in ...
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3answers
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Velocity of massless particles

Due to the equation $E = \frac12{mv}^2$, can a massless particle travel at an infinite speed in a vacuum (as its mass would be $0$ so its energy would also be $0$)?
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Ultimate Speed limit [duplicate]

I've been studying the chapter 'relativity' from this book 'Concepts of Modern Physics by Beiser' where I saw this enclosed article , which says that if u are traveling in a spaceship moving faster ...
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1answer
46 views

How does an object in space travelling at constant velocity have a net force of zero acting upon it?

If the definition of balanced forces is "two opposing forces that are equal" and an object with a net force of zero acting upon it means that the forces are balanced on the object, then it should ...
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1answer
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Using $v_f = v_0 +at$ for objects in free fall [closed]

I have a question about the difference of using $v_f = v_0 +at$ and $s = v_0t + \frac{1}{2}at^2$ for objects in free fall. I'm trying to solve a problem where there's a ball rolling along an inclined ...
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1answer
35 views

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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Angular velocity & acceleration experiment design problem

You know, there is a classical demonstration on the conservation of angular momentum, where you sit on a turning chair with two dumbbells in your hands and push yourself while your arms are open. Then ...
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1answer
57 views

What happens to the fluid flow velocity and concentration in a tube that branches out

Suppose that liquid is flowing through a tube with a constant velocity of, say 10 m/s. Within the liquid, there is a constant concentration of some substance, [S], lets say of 20 uM. Then, at some ...
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1answer
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Why is velocity mathematically describes as a division? [duplicate]

I want to know why, in kinematics, is velocity described as $v = \frac{\Delta x}{\Delta t}$, and why it is not described as any other expression (like a multiplication), why does a division is the one ...
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Explanation of Weber's law

In equation (7) of the following article: Gravitational Induction with Weber’s Force The acceleration as a function of position is: $w = \frac{2GM}{Rc^2} \frac{d\Omega}{dt}$ Is $\frac{d\Omega}{dt}$ ...
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4answers
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With what velocity are we moving along the time dimension?

Does the question make sense? Velocity along time axis means $v_t=\mathrm dt/\mathrm dt$? If it doesn't, please explain where the flaw is. Taking time as measure like length? Or do we need to ...
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5answers
764 views

Why does relativistic velocity subtraction produce a larger relative velocity than classically?

I got a question for homework saying that there were two rockets on a parallel track, heading towards earth. Rocket A was in front of Rocket B. Rocket A was travelling at a velocity of $0.75c$ from ...
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0answers
50 views

Showing that $4$-velocity and $4$-acceleration are mutually perpendicular in special relativity

The following is said in Landau and Lifshitz I'm trying to understand how we arrive at formula $7.4$. In my class a different approach was taken if we let $$u^a = \frac{dx^a}{dt'}$$ where $dt' = dt \...
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2answers
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Why is force related to acceleration instead of velocity?

I know $F=ma$, but it's never really made sense to me. Here's an example: Hypothetical scenario- I push a bowling ball ($m = 4\,\rm kg$) sitting on the floor with $5\,\rm N$ of force. (Assume no ...
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1answer
109 views

Using the Minkowski metric show that $u_au^a = -c^2$

Using the Minkowski metric show that $u_au^a = -c^2$. I am trying to solve the above problem. Firstly $4$-velocity can be defined as $$u_a = \frac{dx^a}{dt'}$$ where $dt' = dt\sqrt{1-\frac{v^2}{c^2}...
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2answers
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1answer
231 views

How is the power of water flowing through a pipe directly proportional to $v³$ and not $v²$?

How is the power of water flowing through a pipe directly proportional to $v^3$ and not $v^2$? (Where $v$ is the velocity of water) I have been trying to write power in terms of $v^3$ but I'm ...
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1answer
47 views

Is this Question correct? Newtonian Motion - Relative Motion of Rain

There is a question in a textbook which states: "A cyclist is riding north at 12km/h when it starts to rain. The rain appears to be falling towards her at an angle of 10 degrees relative to the ...
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4answers
192 views

What is the fastest possible acceleration?

Context & Question In physics, the fastest possible speed is accepted as the speed of light. No other mass has been recorded to travel as fast as the photon. What is the acceleration of the ...
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What is the direction of velocity at different points in an elliptical orbit? [duplicate]

Consider an elliptical orbit. We know that the direction of velocity is fully tangential at periapsis and apoapsis. But what is the direction of velocity at other points on the elliptical orbit?
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When is the group velocity of a wave packet the velocity of energy flow?

In particular, I'm asking this for anisotropic media
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0answers
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How to equate the string tension of a racquet to coefficient of restitution?

I'm a tennis fan and wanted to see the relationship between the string tensions of the racquet and the velocity of the ball after it bounces off the racquet. I used the coefficient of restitution ...
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3answers
122 views

Why speed = distance/time? [duplicate]

Is it merely an arbitrarily chosen definition that we created in order to quantitatively measure the speed of an object or is it some other way around. I want to know what's the reason behind such a ...
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1answer
49 views

A Question about Index Notation of a Scalar Product [closed]

Could anyone please explain why an index $k$ is added to the scalar product of the velocities (squaring the velocity) in the figure below? Can't we use the same index $j$ for the second factor? $$\...
2
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1answer
51 views

What is the fastest tangential velocity?

What is the fastest tangential velocity, that was reached by a man-made object? I have only found examples of angular velocity. More specifically, I am looking for the speed of the rim of spinning ...
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1answer
43 views

Speed of light, can it be not constant? [duplicate]

What if we switch on a flashlight while travelling at the speed of light (we are travelling in vacuum, in a straight path)? What will happen and what will be the speed of light from the flashlight? ...
2
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2answers
57 views

What part of special relativity is factored in in relativistic redshift velocity equations?

While doing research into redshift equations (doppler redshift and cosmological redshift), both types of redshift had two equations for finding recession velocity: a 'non-relativistic' equation and a '...
2
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4answers
116 views

Is there a concept of velocity at quantum level? [duplicate]

I am confused as according to Heisenberg's uncertainty principle, we cant define the position and momentum of a particle with absolute accuracy simulaneously. Then how can we define velocity at ...
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1answer
89 views

Additive speed of light for three bodies

I know this question, or similar ones have likely been asked before, but I have tried reading several, and they just don't properly explain what I'm trying to understand. The quick version of the ...
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3answers
72 views

Can average acceleration be exactly determined from discrete points separated by equal time intervals? [duplicate]

I am using the American dialect of the English language. The following definitions distinguish my question from the similar, previously asked question: https://ahdictionary.com/word/search.html?q=...
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4answers
3k views

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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0answers
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Can some one explain following formula for average impulse of a molecule in the derivation of Boltzmann–Gibbs distribution

Thus, the total average impulse contributed by a molecule with an $x$-component velocity ranging between $v_x$ and $v_x+\mathrm dv_x$, is given by $$2mv_x\cdot\frac{v_x\tau}{L_x}\cdot\sqrt{\frac{\...
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Confusion about 4-velocity

I know that 4-velocity is defined as $$u^\mu = \frac{dx^\mu }{d\tau}$$ $$u_\mu=g{_\mu}{_\nu}u^\nu$$ and $$u_\mu u^\mu=c^2$$ Is it true that $$\frac{d\tau}{dx^\mu} = \frac{u_\mu}{c^2} = \frac{1}{c^...