Questions tagged [velocity]
The time rate of change of the position of an object
2,356 questions
3 votes
5 answers
237 views
Proof and meaning of $\vec{v} = \vec{\omega}\times\vec{r}$
Elementary question but I'm slightly confused about the statement $$\vec{v} = \vec{\omega}\times\vec{r}.$$ I know that $\vec{\omega}$ is simply the time derivative of $\theta$, which, to make things ...
4 votes
1 answer
153 views
Deriving 1D Einstein velocity addition from group axioms via boundary-fixing Möbius boosts (standard reference?)
In 1D the Einstein velocity addition law$$u\oplus v=\frac{u+v}{1+\frac{uv}{c^2}}$$is often introduced via Lorentz matrices and rapidity. I’m after a group-axiomatic derivation that starts instead from ...
0 votes
1 answer
145 views
A technical question regarding forward passes
I am a mathematician writing an article on rugby league forward passes and am looking for a little help from a physics guru. Issue is this: If I am standing on the 25 metre line and pass the ball ...
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1 vote
1 answer
75 views
Is it correct that you can change light's velocity but not its speed? [closed]
A laser is shone down the center of a vacuum corridor 1 light-year in length. The corridor has a lateral motion (perpendicular to the laser) of 10mph. Does the light hit the center of the far end, or ...
6 votes
2 answers
792 views
Does the constant horizontal velocity of a projectile with relativistic velocity components reduce as it accelerates downward?
Assume an electron/proton is shot perpendicularly into a huge uniform electric field with a constant horizontal velocity of a considerable portion of the speed of light ($v_x=0.8c$). As it accelerates ...
- 2,920
1 vote
1 answer
173 views
Analysing $a$ = $v\frac{dv}{dx}$ expression in 1D linear and 2D curvilinear motion cases
$a$ = $v\frac{dv}{dx}$ This is a well known formula for acceleration in 1D motion cases. And it gives total acceleration in 1D cases. Please correct me if I'm wrong. When it comes to a general 2D ...
- 956
0 votes
0 answers
55 views
An object cannot travel faster than the speed of light, but what about the relative motion of two object traveling in opposing vectors? [duplicate]
If mass m1 is traveling along vector v1 approaching the speed of light. and mass m2 is traveling in a directly opposite vector v2 approaching the speed of light, considering only contemporary ...
- 153
3 votes
2 answers
305 views
Is relative velocity necessarily symmetric? [duplicate]
In his 1905 paper, when Einstein posits a relative velocity v between two frames, he assumes that each frame will get the same number. Is this necessarily true, tautologically? That is, if they ...
- 385
0 votes
4 answers
199 views
Difference between average speed & magnitude of average velocity [duplicate]
I don't understand why the car's average speed is exactly 40km/h but the magnitude of average velocity is not. Why is the magnitude of average velocity less than 40? Can you tell me what the average ...
- 69
2 votes
1 answer
172 views
Definition of spatial twist of a rigid body
I am learning about spatial twist $\mathbf{V}_{AB}^s$ from MLS(A Mathematical Introduction to Robotic Manipulation). MLS defines the linear component of spatial twist defined as: $v_{AB}^s$ is the ...
- 153
1 vote
0 answers
126 views
How does the area under the Velocity-Time graph represent the magnitude of displacement? [closed]
For constant velocities where $a=0$ the area is simply given by the area of the rectangle enclosed between the velocity and the time (i.e. $v * t = x$). And for accelerated bodies we simply imagined ...
1 vote
3 answers
262 views
Can the speed of the wind be determined from a photo or video of a flag?
When a flag moves around in a wind of constant speed can we determine wind speed from the flags distorted shape or angle it is flying at? Perhaps this video of a flagpole vortex can help Flagpole ...
user439184
0 votes
3 answers
258 views
If every body on earth moving at constant velocity is subject to balanced forces then why isn't a body's acceleration as well?
My question is basically in the heading but I'll try putting it better. If every constant force causing a body to move at constant velocity on earth and in other environments are subject to friction, ...
- 1
9 votes
3 answers
3k views
Am I getting closer to the car in front if they are moving at a faster velocity but decelerating faster than me? [closed]
Let's say there is a car in front of mine on a straight motorway and its speedometer is showing 100 mph while mine is showing 80mph. But it's decelerating at 10mph/s, while mine is decelerating at ...
- 535
0 votes
1 answer
124 views
Velocity from 2 frames of refrence [duplicate]
Take a body that is stationary to a universe with 11 bodies in it, where all bodies are at rest and have a mass of 2 kg. Accelerate one body (A) to 1 m/s. With the prinicple of equivalence, doesn't ...
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