The velocity tag has no wiki summary.
11
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2answers
726 views
How fast would a spaceship have to go to reach Alpha Centauri within a person's lifetime?
Given the recent news about the discovery of an "Earthlike" planet orbiting Alpha Centauri (our nearest stellar neighbour) it got me wondering just how fast would spaceship have to travel to be able ...
11
votes
2answers
449 views
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. ...
8
votes
1answer
2k views
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 ...
7
votes
9answers
6k views
Why does the mass of an object increase when its speed approaches that of light?
I'm reading Nano: The Essentials by T. Pradeep and I came upon this statement in the section explaining the basics of scanning electron microscopy.
However, the equation breaks down when the ...
7
votes
5answers
440 views
How can kinetic energy be proportional to the square of velocity, when velocity is relative?
Let's start with kinetic energy (from los Wikipedias)
The kinetic energy of an object is the energy which it possesses due to its motion. It is defined as the work needed to accelerate a body of a ...
6
votes
4answers
754 views
Double light speed
Let's say we have 2 participles facing each other and traveling at speed of light
Let's say I'm sitting on #1 participle so in my point of view #2 participle's speed is c+c=2c, double light speed? ...
6
votes
8answers
484 views
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.
...
6
votes
4answers
465 views
How to brake 'beautifully'?
Sometimes when I'm driving my car, I play a "game" against myself in which I try to minimize the deceleration felt by passengers (including myself) while still braking in a reasonable short space. I ...
6
votes
6answers
545 views
When driving uphill why can't I reach a velocity that I would have been able to maintain if I started with it?
Consider these two situations when driving on a long straight road uphill:
Starting at a high velocity $v_h$, which the car is able to maintain.
Starting at a lower velocity $v_l$, and then trying ...
6
votes
6answers
422 views
How low can an electron go?
Title says it all - recently I encountered a strange homework exercise on de Broglie dual theory with an electron wavelength of few millimeters - which implies the velocity lower than 1 m/s. I ...
5
votes
2answers
254 views
Explanation that air drag is proportional to speed or square speed?
A falling object with no initial velocity with mass $m$ is influenced by a gravitational force $g$ and the drag (air resistance) which is proportional to the object's speed. By Newton´s laws this can ...
5
votes
4answers
656 views
A Basic Question about Gravity, Inertia or Momentum or something along those lines
Why is it that if I'm sitting on a seat on a bus or train and its moving quite fast, I am able to throw something in the air and easily catch it? Why is it that I haven't moved 'past' the thing during ...
5
votes
2answers
781 views
Escape Velocity of Asteriod 243 Ida
I was reading about this asteroid (apparently, it has a moon, isn't that awesome?) and I started thinking about if I was on this asteroid, and I jumped, would I fall off?
It's been a while since I ...
5
votes
3answers
363 views
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 ...
5
votes
1answer
88 views
Aircraft nose-up glide
In the pilot's introductory book "Stick and Rudder" it claims that a nose-up glide is possible. It doesn't state how, why or when. It implies it's possible to do and maintain a constant forward ...
4
votes
4answers
258 views
Terminal velocity of all falling objects is same?
Ideally 2 objects of different mass and weight will hit the floor at same time because they face same gravitational pull and accelerate. Will the terminal velocity of both objects be same also? and ...
4
votes
2answers
361 views
Is instantaneous velocity an abstraction?
In introductory analysis, the discussion the derivative emphasizes that while average rates of change are measurable, instantaneous rates of change are a "limiting abstraction". While this makes ...
4
votes
2answers
92 views
What's the physical difference between the quantities $\langle v_{i}v_{j}\rangle$ and $\langle v_{i}\rangle\langle v_{j}\rangle$?
What's the physical difference between the quantities $\left\langle v_{i}v_{j}\right\rangle $ and $\left\langle v_{i}\right\rangle \left\langle v_{j}\right\rangle $?
Where $\left\langle ...
4
votes
2answers
214 views
What does this observation of instantaneous velocity in Brownian particles mean?
I read this artice: Physicists Prove Einstein Wrong with Observation of Instantaneous Velocity in Brownian Particles
“We’ve now observed the instantaneous
velocity of a Brownian particle,” says
...
4
votes
2answers
2k views
Flow of liquid among branches
If water is flowing through big pipe is branched into 4 branches of small pipe. Lets say the flow is around 4 m/sec.
I have the following questions:
What will be the flow rate in each of the ...
3
votes
2answers
880 views
How to deduce the theorem of addition of velocities?
Lorentz contraction and time dilatation can be deduced without Lorentz transformation. Can you deduce also the theorem of addition of velocities
$$w~=~\dfrac{u+v}{1+uv/c^2}$$
without Lorentz ...
3
votes
2answers
273 views
Is the escape velocity at Geosynchronous Earth Orbit 0km/hr?
Follow-up question to How long must escape velocity be maintained?
Is the escape velocity at GSO 0?
3
votes
2answers
616 views
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.
3
votes
3answers
866 views
Is it possible to calculate weight of person with sensors found in today's smartphone?
Is it possible to calculate the weight of a person by only
using his smartphone, some action he must perform (jump, rotate etc.) and
some data like his height or age.
Current smartphones have the ...
3
votes
2answers
334 views
How much does it cost every time your car stops for a traffic light?
Every time we have to stop the car, it is costing us extra money, because we have to then accelerate to full speed again. I would like to know how much.
In order to simplify the situation, we can ...
3
votes
3answers
196 views
Is velocity quantized?
If velocity is not quantized, then do moving objects have 'infinitely decimal place' velocities which we just can't measure to infinite decimal places? From my understanding the quantization of ...
3
votes
3answers
1k views
What is the physical meaning of diffusion coefficient?
In Fick's first law, the diffusion coefficient is velocity, but I do not understand the two-dimensional concept of this velocity. Imagine that solutes are diffusing from one side of a tube to another ...
3
votes
1answer
105 views
Does a fly get brought up to speed with a bus?
Consider a scenario where a bus is moving at a constant speed and a fly enters through a window,the fly is also flying at a constant speed.
Since the bus is not in contact with the fly and neither is ...
3
votes
1answer
837 views
what is uniform velocity?
i have a very basic question from school days. what does it mean to say an object is moving with uniform speed? it seems to me now that it should be an unit dependent concept.
for example if speed is ...
3
votes
1answer
305 views
How do I find the initial velocity in this problem?
An X-ray tube gives electrons constant acceleration over a distance of $20\text{ cm}$. If their final speed is $2.0\times 10^7\text{ m/s}$, what are the electrons' acceleration?
I know this ...
3
votes
2answers
594 views
Group Velocity and Phase Velocity of Matter Wave?
In quantum mechanics, what is the difference between group velocity and phase velocity of matter wave? How can it also be that phase velocity of matter wave always exceeds the speed of light?
3
votes
2answers
164 views
Air velocity in a double-skin facade
I was wondering how the air flows in a double skin facade? Say I have a glass facade with a depth of 1m, a height of 200m and a width of 10m. It is a single vertical shaft all the way up with openings ...
2
votes
4answers
545 views
How long must escape velocity be maintained?
Escape velocity from Earth's surface is 11.2 Kilometres/second
How long would one need to maintain this escape velocity to actually escape Earth's gravitational pull? Must this 11.2 km/s velocity ...
2
votes
3answers
839 views
What is terminal velocity?
What is terminal velocity? I've heard the term especially when the Discovery Channel is covering something about sky diving. Also, it is commonly known that HALO (Hi-Altitude, Lo-Opening) infantry ...
2
votes
4answers
292 views
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 ...
2
votes
3answers
139 views
Why do people claim electrons are accelerating
A lot of text books mention that one of the reasons that classical mechanics failed to explain atomic and subatomic processes is that electrons which accelerate should release energy in the form of ...
2
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4answers
217 views
Are circularly defined {velocity, distance, and time} a problem in physics?
In order to measure velocity, one needs a calibrated measuring stick and clock. But in order to calibrate a measuring stick you need a calibrated clock and velocity. And in order to calibrate a clock ...
2
votes
4answers
904 views
Physics behind Wheel Slipping
Lets say that I'm in a car and I apply full acceleration suddenly. Now, the wheels would slip and hence the car doesn't displace much.
But If I start with some constant acceleration, slipping doesn't ...
2
votes
3answers
784 views
What is the velocity area method for estimating the flow of water?
Can anyone explain to me what the Velocity Area method for measuring river or water flow is?
My guess is that the product of the cross sectional area and the velocity of water flowing in a pipe is ...
2
votes
1answer
226 views
whats the rate of energy increase required for constant acceleration between 0.0c and 0.99c?
I was wondering how much energy would be required to accelerate 1000kg to 0.99c at 1G.
What I don't understand is what the rate of increase of energy is required as velocity increases. I was looking ...
2
votes
3answers
251 views
Train crash: are these situations alike?
I was just wondering... I believe that if a car travelling 50 miles per hour crashes into a wall, the result should be the same as crashing to another car also travelling 50 miles per hour (but in the ...
2
votes
1answer
165 views
Motion is relative, right? And most pop sci relativity explanations are somewhat incorrect?
On page 20 of A Brief History of Time:
. . . all observers should measure the same speed of light, no matter
how fast they are moving.
But in an observer's frame of reference, they're actually ...
2
votes
1answer
314 views
Concept of relative speed
I am traveling on a train running at a speed of 100mph. If from the train I shoot a ball at a speed of 100mph in opposite direction then what would be the speed of the ball with respect to a person ...
2
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2answers
1k views
Mass of particle near light speed in a medium
I am trying to get a common understanding from these two previous questions:
Why does the mass of an object increase when its speed approaches that of light?
What happens if light/particles exceeded ...
2
votes
3answers
189 views
If you could reverse gravity, what velocity would you achieve on leaving Earth?
If you could reverse gravity, to make it repulsive instead of attractive, what velocity would you achieve on leaving Earth? A simple question really, but I have completely forgot how to calculate ...
2
votes
1answer
244 views
From how deep into space can a human “skydive” back to earth? [duplicate]
Possible Duplicate:
From how high could have Felix Baumgartner jumped without disintegrating like a shooting star?
If a human can skydive from an altitude of 24 miles (39 km), and a ...
2
votes
2answers
467 views
Velocity of Voyager 1
I was reading Wikipedia which stated
....Voyager 1's current relative velocity is 17.062 km/s, or 61,452 kilometres per hour (38,185 mph).....
It travels away from sun. So sun's gravity must ...
2
votes
3answers
2k views
Velocity and acceleration question
1.The magnitude of the total force acting on a ball rolling without
slipping down a ramp is greater than
the magnitude of the total force
acting on the same ball if it slides
down the ramp ...
2
votes
1answer
99 views
Need help with the position of a particle in a velocity-versus-time graph
I am having trouble with a velocity-versus-time graph. I recently took a Physics test that asked this question: The graph shows the velocity versus time for a particle moving along the $x$ axis. The ...
2
votes
2answers
98 views
Where are we : On level ground or on a ramp - moving in a train?
Let's say we are traveling in a train. The path has two parts: one at ground-level and the other moving up on the ramp. The ramp has an inclination of $\arctan\frac{a}{g}$ with the horizontal, where ...
