Questions tagged [speed]

Scalar quantity which is the magnitude of velocity.

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Instantaneous speed x instantaneous velocity

Related to Distinguish between instantaneous speed and instantaneous velocity I understand that the average velocity is given by the displacement divided by the change in time, and it is a vector ...
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How to calculate the time derivative of electromagnetic field? [closed]

How can I calculate the time derivative of an electric field from its space derivative? That is, I know $\frac{dV}{dx}$, and I need $\frac{dV}{dt}$. In general, $\frac{dV}{dt}$ = $\frac{dV}{dx} \times ...
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Can you calculate for how much force is needed to bank an airplane with a given airspeed and mass? [closed]

This is similar to that was previously at equilibrium, just with air pressure and speed added on. I want to see how much force would be needed to remove the equilibrium and bank the airplane. Is this ...
Sam Jones's user avatar
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Question about light and distance

If we see into the past with light and distance travelling so we can’t see things how they are currently, only how they were in the past; and James Webb took a photo from the beginning of the universe ...
Mary Cox's user avatar
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What's the limit on the length of string that can be pulled by a person? [closed]

Imagine it's pre-industrial times, and a king wants to keep control of his vast empire. One of the biggest problems was how slow it was to transmit information; it could take weeks to be notified of ...
Reuben Matthews's user avatar
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Why is it that objects inside a moving train tend to move at the same speed as the train itself?

I mean I get people saying because it's Newtonian mechanics. Everything inside the train will have same speed as that of train but my question is why ? Why is it like that ? And How does that happen ? ...
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What's the fastest speed water from a glacial dam burst could achieve? [duplicate]

I've been watching a lot of Graham Hancock videos of late, thrusting myself deep into the rabbit hole of pseudoarchaeology/alternative archaeology, and I don't really know enough to assess the ...
Josh Hills's user avatar
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What does instantaneous velocity mean? [duplicate]

What does instantaneous velocity mean? on google it says "Instantaneous means something happens very quickly, in a single moment. It's similar to the meaning of "instant", but most ...
Intensed's user avatar
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What would happen to a person's body if they were struck with a meteorite?

Considering that this is a meteorite that has broken through the Earth's atmosphere, what would happen to one struck by a meteorite? Not a large one of any sort, but one around the size of a fist. How ...
CrimsnComet's user avatar
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Can field itself have a speed?

I've seen many examples about a particle moving relative to field. But I never saw a field moving relative to observer (or a particle). So, can field have a speed? I thought about some possibilities: ...
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Speed of sound confuses me

Just a random question out of interest. When you hear an explosion, e.g. a firework, firecrackers etc, from far awa how does the sound reach our ears so quickly? The speed of sound in air is like 300m ...
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The proportionality of a Drag force and speed

At low speeds, Drag force is proportional to speed due to Stokes law. At higher speeds, Drag is proportional to the square of speed. While modelling the speed of a water rocket, I realised that when ...
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Product of two 4 positions without writing the components

I was able to solve the first part of the following question by expanding the terms as vectors I can't understand how to do it without expanding so I had a look at the answers. I understand how we ...
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How can we accurately tell distances of celestial bodies when considering superluminal expansion [closed]

If parts of the universe are moving away from each other faster than the speed of light relative to my position in space, how can we accurately tell the age or distance of other celestial bodies ...
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Funneling air into a small opening, calculating time of speed differential

Assume I have a funnel that fits a rectangle air vent of 1" x 4" with an opening for a circular tube of 0.5" diameter. After connecting a 0.5" diameter x 2 ft tube to the funnel, ...
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How can light have a speed when it devies what speed is?

For us to measure any movement, the "something" has to have a different position to some reference frame. now speed is defined by the amount of changed position( which we can tell by the ...
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What's the speed limit for things with mass?

So the speed limit of the universe is 299 792 458 m/s, but only massless things like photons can archieve this speed. Since things that have mass can reach 99.99999...% speed of light, does that mean ...
comp_guy_dude's user avatar
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Why is it more difficult to turn the steering wheel of a stationary car than a moving car? [duplicate]

I believe anyone who has driven a car without power steering has noticed this effect. I am not able to find a justifiable argument online. My thought process suggested it must have to do something ...
Avish Bhatia's user avatar
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Why does force decrease with increase in velocity in case power was constant?

Suppose an internal combustion engine burns the same amount of fuel every cycle (regardless of engine or car speed ) that means it creates the same pressure every cycle and the force on the piston due ...
John greg's user avatar
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Reality of speed and time [closed]

I have a very simple question. How does a faster object takes less time for the same distance? A car with a speed of 100km per hour takes one hour to travel 100km while a car with the speed of 50km ...
majid dadmand's user avatar
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How long does it take before neutrino velocities in the neutrino background radiation are substantially less than the speed of light?

The energy of photons is reduced by the expansion of space. Since the photons have been decoupled from matter their wavelengths have decreased from the visible range to the radio range. The same ...
Il Guercio's user avatar
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What are the exact conditions for the constancy of the speed of a wave?

Do two mechanical transverse waves traveling in the same medium have the same speed whatever the source might be? If the answer to this question is yes, can I generalize and say "all waves of the ...
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In circular motion is acceleration vector and $\frac{dv}{dt}$ the same?

I was studying a book in which they have written this $$ a = -w^{2} r \hat{e} + \frac{dv }{dt} \ddot{e} \tag{1} \label{1}$$ Where $a$ is acceleration vector $\hat{e}$ is unit radial vector and $\ddot{...
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If mass was to reach the speed of light it becomes infinitely heavy. Does this mean it has become a black hole singularly? [duplicate]

If mass reaches the speed of light, it becomes infinitely heavy. Does this mean that it has become a black hole singularly?
Morbo Guano's user avatar
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Why the free Lagrangian does not dependent on the velocity vector direction, only its speed?

For freely moving particle, It's said $L$ can't depend on the velocity vector, but only its magnitude. Question: I'm looking for the contra-argument. Let's say $L$ depends on velocity vector. Then, ...
Giorgi's user avatar
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What does the square in kinetic energy formula imply? [duplicate]

I was wondering if the velocity squared imply that you need exceedingly more energy to gain speed. And if so, why is this a thing?
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Average angular velocity and speed

Are the magnitude of average angular velocity and the value of the average angular speed always same? If not then can you please give an example.
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How long does it take to hear the sound of a plane that travels at the speed of sound?

in our physics lessons we often learn how to calculate the time that sound of a plane that travels faster than sound takes to reach us using the Mach cone. But can we use the same method to calculate ...
Chamodh Nethsara's user avatar
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How Long For An Object To Catch Up To Another Object Moving At Different Speeds? [closed]

Example: A bear is 10 m away from a person, the bear is moving at a speed of 15 m/s, the person is moving at a speed of 6 m/s, how long would it take for the bear to catch up to the person? I'm not ...
burner8268's user avatar
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Sound speed profile

The research vessel on the large and deep ocean sends sound waves into the depths at various angles of incidence and measures the distance at which the sound reemerges (which always happens because ...
Edward Henry Brenner's user avatar
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How fast can the human hand move?

I was playing with my six year old daughter the other day with her toy airplanes (I’m a pilot and she’s very interested in aviation now). I took the little F16 toy and flew it passed her as quickly as ...
Cjh199712's user avatar
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5 answers
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Speed and Velocity

Why did physicists develop the concept of velocity? I searched on the web, but I didn't get a satisfactory answer. All I got is that velocity has a direction whereas speed does not. Why do we need ...
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Shooting a bullet in motion

If a bullet is shot from a firearm from a moving car in the direction of movement, would the speed gained with respect to the car be same as the speed of a bullet that is shot from an immobile gun? I’...
EvgenySizov's user avatar
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Is increase in current speeding up the electrons or is it just focusing velocities of electrons in the same direction?

Current in a wire is defined as the amount of charge that passes through a cross-section of that wire in a single second. By this definition alone, it is clear that a current relies on the motion of ...
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Relative velocity in the air frame or platform frame?

In "Introduction to Classical Mechanics: With Problems and Solutions" by David Morin he describes the following scenario: Let $ v_s $ be the speed of sound in air. Imagine two people ...
Jon's user avatar
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Can $d/t =$ speed ever be wrong? Is there a more accurate way to determine speed?

Is there a more accurate way to determine speed? I am asking because this has to do with an accident reconstruction where my son was killed. The investigators are trying to conclude his speed prior to ...
Dayle Suzanne's user avatar
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Is 'rest mass' same for every observer/perspective? [duplicate]

(This is a quick one) Suppose Im standing still (in my perspective) and a hoverboard is flying at $0.8c$ w.r.t me. I see that the ball (red) is moving at $0.8c$. I measured earlier that the ball is $...
Rohit Shekhawat's user avatar
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2 answers
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Explain the equation

Can someone explain me this equation. This is braking distance equation that applies all reaction times ect.. Taken from Bosch Automotive Handbook. But what does the 25,92 mean there? v= velocity tvz =...
wtknow's user avatar
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Average acceleration to distance travelled. Equation gives wrong answer

i wanted to verify the measured data with calculations. So i got two totally different answers when calculating average acceleration. V0 = 0 km/h Vf = 30 km/h = 8.33 m/s t = 9.32 s S = 55.59 m So &...
wtknow's user avatar
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$E_k = (1/2) mv^2$ doesn't make sense to me [duplicate]

I hope this is the right platform to ask stupid questions like this, but this is driving me nuts right now. Probably embarrassing to say, but I actually have somewhat of a physics background, but also ...
TLeksl's user avatar
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3 answers
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Why varying the frequency of a propagation wave in a non-dispersive media doesn’t change it’s propagation velocity?

Why varying the frequency of a propagation wave in a non-dispersive media doesn’t change it’s propagation velocity? Before anything, I want to note that I’ve seen already similar questions on this ...
Xetrez's user avatar
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Why do we take $\langle{v^2}\rangle = \langle{v}\rangle^2$?

In Ashcroft and Mermin's Chapter 1, the equipartition theorem is often used to evaluate the mean speed of an electron in an (ideal) electron gas treated with classical statistical mechanics. That is, ...
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Estimating penetration depth of projectile in nonhomogeneous material

I need an equation for calculating the penetration depth of a projectile in a non-homogenous material. I have the values for density of each layer and the projectile, speed, and angle. Does anyone ...
curiousquail's user avatar
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Does the postulate of special relativity say that speed of light in vacuum is the greatest speed? [duplicate]

The postulate of relativity says that the speed of light in a vacuum is the same for all inertial observers. But does it also say that this speed is the greatest achievable speed?
Solidification's user avatar
8 votes
4 answers
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What does squaring a vector mean?

So,in the 3rd equation of motion,i.e $v²=u²+2as$,what does the square on the final velocity and initial velocity actually mean?And how does it make an effect on their direction? suppose upwards vector ...
aiman's user avatar
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Drag force on a bicyclist

Recently, I wrote an introductory physics exam where I encountered the following problem: We look at a bicyclist with the wind drag force $\vec{F_R}(t) = -k \vec{v}(t) |\vec{v}(t)|$ who accelerates ...
arrhenius's user avatar
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2 answers
103 views

When will the 2 cars Have equal speeds? [closed]

If car1 started at 20m, with initial velocity of -4m/s and acceleration of 3 m/s^2. Car 2 started at 15m, with initial velocity of 6m/s and acceleration of 0. At what time will the 2 cars have equal ...
JordenSH's user avatar
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3 votes
2 answers
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Does the wavelength of a sound change from one medium to another?

In my book, it is written that: v = fλ in a given medium under conditions of fixed temperature and humidity. It is also written that: one of the more important properties of sound is that its speed ...
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Car stopping times (not distances)

(Apologies if this is not the correct Stack Exchange site; I was unsure where I should post this question) I was prompted to write this after reading on Reddit the stories told by drivers who had ...
Richiban's user avatar
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Please help me understand the purpose of torque on a straight road

Two exact same cars are running at a constant speed. Car A: 2200 rpm, 2nd gear, 20mph. Car B: 2200 rpm, 3rd gear, 40mph. Same power. Car A has low speed, high torque (due to lower gear). Car B has ...
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