Questions tagged [velocity]

The time rate of change of the position of an object

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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 ...
253 views

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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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 ...
140 views

Law of motion of accelaration applying average velocity

Consider the law of motion of acceleration: $s=1/2at^2$ Develop the law decomposing the acceleration: $s=1/2 * (V/t) *t^2 = 1/2*(V*t) = V/2 *t$ So we can say that the space is the moltiplication ...
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Envelope of wavepacket and group velocity

In this answer a possible derivation of the group velocity is provided. It is, anyway, based on the assumption that there will always be a point where all the cosines will sum with the same phase: ...
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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 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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Definition of velocity in classical mechanics

Let $(r_1,r_2,r_3)$ be the coordinates of a particle $r$ in the coordinate system $\phi$. Let $\{\hat{e_1},\hat{e_2},\hat{e_3}\}$ be the coordinate basis of $\phi$. Why do we define the velocity $v$ ...
63 views

Light Source + Prism in a closed box --> What happens under movement?

Setup: I'm interested in the behaviour of light / the breaking of light in a closed system under movement. I'm sorry in advance if this question is a super-simple, but I just couldn't think of a ...
3k views

How does the size of the hole affect the exit velocity?

I took water bottles and drilled several different sizes of holes on the bottom. During the experiment, I found that the water bottle with a smaller hole takes a lot longer time to leak than those ...
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Velocity Profile of the Upper Atmosphere

Consider an Earth-Centered Inertial (ECI) frame in which the tangential (to Earth's surface) velocity is measured. Now consider obtaining constant average velocity profiles of the atmosphere as a ...
198 views

Velocity of water column

If an air filled tube 5 km long with a diameter of 20 m was submerged vertically under water one end 5 km underwater and the other end at the surface, how fast would the water column rise if the ends ...
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Why did they use two separate vectors to calculate the magnitude and angle of the initial velocity?

The question/solution are on the attached images. (It's dealing with projectile motion) I already understand how to work out part a, but I'm having trouble understanding why they used the final ...
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Lining up fans in a row

Im new to this website, and not extremely educated in the world of physics. I have a very basic (mostly high school, some college) understanding of physics. That being said, I work for the fire ...
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Deceleration of spherical particle in fluid

If I know the initial velocity of a particle entering a fluid, how can I calculate its deceleration over time ? What parameters would I need to know ? Viscosity of the fluid, weight of the particle ......
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Can a projectile moving at supersonic velocities leave a silhouette in whatever it hits?

I was recently reading this, and Floris's answer confirmed my knowledge that the information of an collision travels at the speed of sound. While I was thinking about that, my mind wandered and I ...
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Relativity addition and signs

I have just covered a very brief module on special relativity as a part of my physics course. I have also done some extra reading mostly; Morrin's Classical Mechanics. While I found the book really ...
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How to formally write down the Boltzmann equation?

Can someone write down the Boltzmann equation, not neglecting any of the variables of the involved functions and integrals? Specifically, how to concisely capture the "primed" variables in a sensible ...
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How do we generalize limitations on the propagation speed of sinusoidal waves to limitations for transmitting any kind of information?

Our calculations on EM waves basically deal with harmonic waves and through such calculations and relations, we derive some relations and limitations for wave like phenomena. Of these relations are ...
397 views

Saturn V specific impulse issue in velocity modelling with Tsiolkovsky's equation against actual values?

I've been trying to model the Saturn V's velocity using Tsiolkovsky's ideal rocket equation, and in the process, I think I may have made a mistake with regards to the specific impulse? I've come up ...
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What do the components of light velocity look like in polar coordinates?

The Schwarzschild solution makes use of polar coordinates, and I'm wondering how the different components of velocity of light change with the position. Might I get some examples of light velocity ...
700 views

Finding the terminal velocity of a magnet dropped in a solenoid

We have to find proportionality of the terminal velocity with the factors of the system: Plot: a small dipole(mass $m$) with dipole moment $\mu$ is dropped in a long solenoid (radius $r$, ...
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Is there any place you can safely skydive without a parachute?

While trying to explain to someone how a kitten walked away from a fall from a skyscraper I got to wondering if there's any place a human could do that and I find myself out of my depth. The only ...
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 ...
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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 do we write free body diagram for an object that is rebounding?

How do we write free body diagram for an object that is rebounding? Here's an illustrated example Let us assume that the object has an initial force. So, I want to draw free body diagram for each ...
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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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Forces between wheels and road for a vehicle

Let’s assume we have a front-wheel drive (FWD) car, and we apply a torque (Cf) to the front wheels. At this point, assuming no slip condition, a friction force (Tf) will occur due to friction between ...
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Correlation between velocity and homogeneity of spacetime and isotropy of space

Considering only inertial frames of reference and constant velocities, does the fact that any velocity, with the exception for the speed of light in a vacuum, can be transformed, via an accurate ...
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Minimum Time Through Curve

Consider the following conditions: A level road with the path $\vec{r} = \left<x(s),\ y(s)\right>$ A max speed of $v_{max}$ A vehicle with the mass $m$ Tires with a static friction coefficient ...