Questions tagged [speed]

Scalar quantity which is the magnitude of velocity.

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1answer
46 views

Train speed and closed windows

Most coaches in Indian trains are non-air-conditioned, i.e., the windows can be opened. Recently, the government has planned to convert all coaches in some trains to A.C., citing the fact 1 that for ...
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Data for experiments of Doppler effect

I am a high school student that has attempted to carry out the experiment for the Doppler effect using an RC car going at constant speed, a sound source at constant frequency and phyphox app to ...
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5answers
1k views

Why is it said that speed always remains constant in circular motion?

One can cover circular motion with different speeds at different positions, right? The only aim is to complete his circular motion, right?
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How to use this equation in real life for accurate results?

In this video, you can use the equation to solve for the distance between the ball being dropped and when it hits the ground. All you need to know is the time it takes and the gravitational ...
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1answer
60 views

How much will rolling bodies like cylinders set on a surface of a fast moving body attenuate its friction with atmosphere?

A car, train or a spacecraft feels a certain drag when moving through the atmosphere. I think that rolling bodies produce less drag, and hence, my question is why rolling bodies as little spheres or ...
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About the meaning of an equation on the book 'Classical field theory' of Landau & Lifshitz

In the chapter 'Constant gravitational field' of the book 'Classical field theory' of the authors, there is the following equation: $$v=\dfrac{dl}{d\tau}=\dfrac{c}{\sqrt{ g_{00}}}\dfrac{dl}{dx^0}$$ ...
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Why does it take more energy to go faster to the same place? [closed]

Edit: to people asking about details, I am not asking about drag. Take it to happen in vacuum, space, no drag, no other forces. I would like a general rule of thumb. This guy with e equals mv squared ...
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1answer
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What angles of releasing a pendulum will affect the speed of a spherical object hit by it? [closed]

I tried to search for papers for similar experiments but I couldn't find any. Could someone please help me find resources for my experiment. It would also be great if someone could give some ...
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Calculate wind speed on each wind turbine on a wind farm considering consecutive wake effect

We, as a team, are working on a genetic algorithm related to wind farms layout and for this we obviously require to know the wind speed of each wind turbine given: Constant input wind speed. Same ...
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28 views

Feynman lectures on physics vol 1: Speed as a derivative (8-3)

I have some trouble understanding what Feynman says here: "The procedure we have just carried out is performed so often in mathematics that for convenience special notations have been assigned ...
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2answers
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Speed of a standing wave

Standing waves are the waves in which disturbances do not simply propagate forward or backward, but rather the material particles are moving up and down continuously, with the particles between two ...
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1answer
59 views

How much anti-matter (combining with matter) is needed to give a rocket a velocity that approaches the speed of light (say 95 % of c)? [closed]

A question (very hot presently) about the propulsion of a rocket with compressed air prompted me to ask a somewhat related question. Maybe one sunny day it will be possible to construct an anti-matter ...
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Does adding weight to a person affect the time taken for a person to run 20 metres?

I am doing a science experiment to see if adding weight to a person affects the time taken for a person to run 20 metres. I am needing to write some background information (1 page) and I am not too ...
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2answers
139 views

How can I calculate deceleration due to friction?

I was wondering, how can I calculate the decelerations of an object due to friction - and therefore find the maximal distance it can reach? For example, if a car suddenly brakes in the middle of a ...
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1answer
28 views

Ocean waves breaking slowly at the shore during periods of turbulence

During storms, I have often watched ocean waves breaking at the shore as if they were in slow motion. I've wondered if the slow curling of the waves during these times was somehow due to their ...
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How relative is speed?

A short question, because the math got me confused. If in my inertial reference frame, I see a dude going away from me at a speed $v$. Then, from his frame of reference (which is also inertial) he ...
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2answers
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How can speed be the magnitude of velocity

Say speed is the magnitude of velocity then: \begin{align*} v &=\left|\vec{v}\right|\\ \frac{D}{\Delta t} &= \left|\frac{\Delta \vec{x}}{\Delta t}\right|\\ \end{align*} since $\Delta t$ is ...
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Spinning Top revolutions calculations [closed]

Is it possible to calculate spinning top revolutions per minute? Will the Spinning top material make a difference to the speed revolutions per minute? Example : Wood, Plastic, Steel etc
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3answers
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Suppose there is a vector $\vec v$ which is a function of time, then will $\dfrac{d}{dt}|\vec v|$ be a vector quantity or a scalar quantity?

Suppose there is a vector $\vec v$ which is a function of time, then will $\dfrac{d}{dt}|\vec v|$ be a vector quantity or a scalar quantity? I think it should be scalar because, let's assume $\vec v=...
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2answers
29 views

Confusion regarding the derivation of pressure in Kinetic Theory of Gases

I was studying the derivation of the relation between pressure ($P$) and root mean square speed ($v_{\text {RMS}}$) of an ideal gas from Fundamentals of Physics by Halliday, Resnick, Walker. (The same ...
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2answers
29 views

When height increases then why velocity becomes low?

It's an example. The satellite is moving around the earth. But when its height increases its velocity becomes low
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2answers
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Is there an optimal intergalactical travelling speed? [closed]

In our perceiveable world, an increment of speed typically results in needing less time to travel a given distance. When I go by car, it takes less time then going by bike. However, there is the ...
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1answer
40 views

Laplace correction for speed of sound in air

In the Laplace corrrection for velocity of sound, the bulk modulus is replaced by gamma×Pressure. $(\gamma=c_p/c_v)$ In its derivation $$PV^{\gamma} =\text{CONSTANT} $$ is used. And the reason given ...
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1answer
92 views

Absolute Acceleration in a Train

How would you calculate the total acceleration of a human body that is just starting to walk in the train against the direction of the train, who is also accelerating? Actually I want to have an ...
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1answer
63 views

Given a fixed average speed in the speed vs. distance graph, is it the fastest to travel constantly at that speed?

Is it true that among all the ways to travel a distance $X$ with an average speed $E$ in the speed vs. distance graph, traveling with a constant speed $E$ minimizes the time it takes to complete the ...
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1answer
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Why is the speed of sound wave in a gas always lesser than the r.m.s. speed at the same temperature?

My book says that the speed of sound wave in a gas is always lesser than the r.m.s. speed of the gas at the same temperature. I understand that speed of sound is given by: $$v_s=\sqrt{\frac{\gamma RT}{...
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1answer
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What is the formula for how far a sound can be heard (taking into account dissipation)?

I was trying to figure out how far can a sound of 103 dB can be heard, so I converted it in W/m$^2$ (it gave me about $0.0200$ W/m$^2$) and then I used the formula “$I=P/4\pi r^2$” to find the maximum ...
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2answers
107 views

Is instantaneous speed always equal to the magnitude of instantaneous velocity?

Is instantaneous speed always equal to the magnitude of instantaneous velocity? What about the infinitesimal time duration when the direction changes? How can it ALWAYS be equal?
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6answers
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How is acceleration calculated when only the direction of velocity changes and the magnitude remains the same? [duplicate]

How is acceleration calculated when only the direction changes and the magnitude remains the same? Guys, I know that my previous examples didn’t make sense and I’m sorry because I’m totally new to ...
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5answers
116 views

Why does frequency of a wave depend solely on its wavelength?

On Wikipedia it was stated that a wave's speed $v$, wavelength $\lambda$ and frequency $f$ are related by the identity $$v(\lambda)=\lambda f(\lambda).$$ The function $f(\lambda)$ tells us that the ...
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2answers
50 views

Calculate Earth angular speed [closed]

How may I calculate Earth's angular speed at specific point (The green dot for example)? Note: I know that angular speed $= \dfrac{2\pi}{T}$ But how may I found $T$ in this case? I found too that $R_{\...
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1answer
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What happens if you push an object at the speed of sound?

I believe that if you push an object, say a metal pole, the disturbance travels through the object at the speed of sound in that material. In that case, what happens if you continuously push one end ...
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Acoustic transmission condition - different speed of sound

Given two domains with different speed of sound, what are the acoustic transmission conditions? I know, that there is continuity of velocity and acceleration in the normal direction $$\frac{\partial\...
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2answers
102 views

How long would it take for something really far away, say $300,000,000 \ \text{meters}$, to feel the force from a pull of a rope attached to it?

My friend phrased the original question like this: If I tied a rope to myself and wrapped it all the way around the earth and then pulled (assuming the rope was already taut), which direction would I ...
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1answer
49 views

Object has a certain orbital period and is at perihelion or aphelion. What is it's orbital speed?

I'm writing a simple game, but as you can already see I'm far from being a physicist of any kind. I have a system that calculates and draws orbit of a body with a given orbital speed and distance from ...
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2answers
46 views

Beat frequency when a bat flys towards a wall [closed]

A bat is flying towards a wall while emitting an ultrasound of frequency 25kHz. Emitted sound and the sound that bounces off a wall form a beat frequency 1.65kHz, that the bat detects. With what speed ...
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3answers
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Does weight affect the drag force on a falling parachute?

In my physics class we currently have to do research about a motion and preform an experiment and write an essay on it. The idea I had was to drop two parachutes with different areas from the same ...
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Correct definition of “speed” of gravity

Traditionnal definition of speed in space-time If I understood it correctly (relative to the General Relativity context) a speed is defined relatively to space-time, i.e. we can talk of the speed of ...
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1answer
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Why does the speed of sound decrease with increase in density?

In my book it's written that speed of sound will in increase with increase in density of the medium as molecules with get closer to each other, but after some browsing on internet I found out about ...
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1answer
42 views

How (and why) is energy due to friction independent of speed?

Consider a rotating disk and a fixed part that "abrades" something. Under normal conditions the disk and the fixed part should not touch. However, they slightly touch due to misalignment. When the ...
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3answers
41 views

What does the first derivative of (2-norm) distance with respect to time tell us?

My basic physics' knowledge is a little rusty. My apologies in advance. I know that the first derivative of position or displacement with respect to time is the instantaneous velocity. Suppose I have ...
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1answer
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Is combustion engine power defined by speed and torque?

Of a combustion engine, the speed, torque, and power is measured at the crankshaft. For a measured pair of values for speed $N$ and torque $M$, can there be more than one value for power $P$? In other ...
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2answers
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Do Lorentz transforms use velocity or speed?

Suppose we have the $S'$ frame moving at some velocity $v$ in the $X$ direction relative to the $S$ frame, then it follows $$x' =\gamma (x+vt), t'=\gamma(t+\frac{vx}{c})$$ From my understanding, to ...
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What if the directions of the initial and final velocity are different in the conservation of mechanical energy equation?

I saw a problem, and saw that it could be easily solved using conservation of mechanical energy. So I wrote my equation: $$mgh_1 + \frac12mu^2 = mgh_2 + \frac12mv^2$$ Where $u$ is initial velocity, $...
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Does time travel faster than the speed of light? [closed]

I don't know enough about the subject to know that I am wrong.
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How fast in mph is water when released from dam, a point of exit , as a baseball is clocked in mph when released from a pitchers arm [closed]

How fast in mph is water when released from dam, at point of exit , as a baseball is clocked in mph when released from a pitchers arm . I am a complete novice and looked all over for an answer
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2answers
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When does gun barrel length become too long with a constant pressure?

Just struck out of curiosity, It is a fact that longer gun barrels do increase the acceleration of a projectile, but an infinitely long barrel does not give infinite acceleration. So then, with a ...
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13answers
7k views

Why don't we use rapidity instead of velocity? [closed]

In school we learn that we can add velocities together, and then later on we learn that it's not correct and that there is a speed limit. Why create all this confusion when we could just use rapidity ...
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1answer
95 views

Doubling winch force to gain speed - is it possible?

It's very common to use pulleys or snatch blocks to double the "winching power" - reduce the force needed to move a particular load, at the expense of the speed, given a constant winching rate. ...
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2answers
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What would happen if I rotated an extremely long stick? [duplicate]

(Exclude all movements of myself) Imagine I had a straight stick that reached far out in the universe. If I rotated that stick, what would happen to the speed of the stick and its shape? (First ...

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