# Questions tagged [velocity]

The time rate of change of the position of an object

154 questions with no upvoted or accepted answers
Filter by
Sorted by
Tagged with
2answers
219 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 ...
4answers
237 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 ...
2answers
81 views

### 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 ...
0answers
138 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 ...
0answers
137 views

### 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: ...
0answers
70 views

### 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-...
0answers
45 views

### 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?
2answers
74 views

### 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 $v$ ...
0answers
61 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 ...
3answers
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 ...
0answers
58 views

### 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 ...
1answer
194 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 ...
0answers
82 views

### 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 ...
0answers
1k views

### 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 ...
0answers
366 views

### 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 ......
0answers
94 views

### 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 ...
0answers
256 views

### 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 ...
0answers
140 views

### 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 ...
0answers
58 views

### 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 ...
0answers
391 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 ...
0answers
137 views

### 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 ...
0answers
693 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 $r$, ...
0answers
216 views

### 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 ...
0answers
26 views

### 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 ...
0answers
23 views

1answer
29 views

### 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 ...
0answers
25 views

### When is the group velocity of a wave packet the velocity of energy flow?

In particular, I'm asking this for anisotropic media
1answer
34 views

### 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 ...
0answers
36 views

### 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 ...
0answers
29 views

### 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 ...
0answers
176 views

### Gravity and rotating torus

Questions: Would a spinning torus lose its weight? Would a solid torus, spinning at 7,81 km/s radial speed completely loose it's weight on Earth-like object? Would it 'fly away' at higher speeds? {...
1answer
32 views

1answer
90 views

### Systematic+Random Uncertainty for velocity measurement

I have a question regarding systematic and random uncertainties. I have to measure the mean value of a velocity measurement in flow field at a point. I've recorded say 1000 samples in time, which I ...