# Questions tagged [speed]

Scalar quantity which is the magnitude of velocity.

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### What is the distribution of speeds in an ideal liquid?

By ideal, I mean similar conditions to the ideal gas-in-a-box with perfect spherical perfectly elastic homogenous atoms, so no inter-atomic forces, evaporation, gravity, rotations or phase changes. ...
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### The speed of a QM particle

In the original theory of quantum mechanics what is the speed of quantum particles, I am asking this because photons can only travel at the speed of light C. What about mass particles?
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### How significant is the parabolic arch effected with an incline versus a decline in angle versus a decline in angle . For example throwing a dart

A dart players height can vary as can the height in which they raise their arm to aim. Is there less parabolic arch when throwing at the same strength from above the target compared to below, due to ...
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### Sound Timing: Stationary vs. Moving Source - Who Wins?

Case - 1: A stationary source emits sound and an observer stationary is at 'd' distance apart. Case - 2: A moving source emits sound when an stationary observer is at 'd' distance apart. Will in both ...
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### Friction acting on a moving car

I am trying to understand the nature and direction of friction force acting on from the ground a car driving up an incline. I was thinking about a simple situation where a car of mass $m$ is driving ...
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### Is the drag coefficient linear with speed?

I made an RC-car and wanted to simulate the drag of it in Solidworks. But after I did my simulations I put my results in a graph, the drag is quadratic with speed but the drag coefficient $C_D$ is ...
1 vote
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### Can you make a car powered by 4 car air jacks? Using the mechanics of a manual pedal pottery wheel

If an air jack can pump up a car using little force, can’t an aluminum air jack spin a plastic wheel barrel car going at least 10 mph? Each wheel will have an air jack that uses the mechanics of a ...
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### Speed is equal to distance divided by time but is this correct?

In this study https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9784821/, the distance the punch travelled from start to impact is 0.49 meters and the time taken from start of punch (that's it, they define ...
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### Is there a different way to measure speed, other than with time?

A second on Earth is different from a second on the Sun and a second next to a black hole. Therefore speed, as measured in meters per second, is different in each of these locations. Is there an ...
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### How fast does information travel through air molecules?

You're always told that information travels through air (speed of sound) at appx. 767 mph. This doesn't tell you how fast the transfer of momentum happens between the actual molecules of air. So how ...
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### Is it possible to have a uniform speed but variable velocity in one-dimension motion?

Is it possible to have a uniform speed but variable velocity in one-dimension motion? I saw a lecture where teacher said that it is possible if particle changes its direction of motion 180$^\circ$. ...
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### Rotational speed using conservation of angular momentum

I know that angular momentum is conserved, but I don't know how to calculate the new speed of an object after it shrinks. Say you have a spinning object, then it shrinks, then how do you calculate the ...
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### Why is velocity used for kinetic energy instead of speed? [duplicate]

This may seem like a self-explanatory question, but if kinetic energy is a scalar quantity, and squaring the velocity essentially removes its vector quality, why not use speed instead? I have a hunch ...
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### In this conservation of momentum problem, where is the sign error coming from?

Say I have a particle travelling in the $x$-direction and breaking into two pieces: Conservation of momentum in the $x$-direction obviously gives: $$mv = m_1 v_1 \cos(30) + m_2 v_2 \cos(60).\tag{1}$$ ...
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### Northern lights / aurora borealis "pre-warning" - how does this work w.r.t timing and different particle / wave speeds?

There is an article in the newspaper today entitled "Northern lights predicted in US and UK on Monday night in wake of solar storms". I assume that the reason that someone can make this ...
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### Who wrote $c = λ ν$ for the first time and where can I find it?

I have been surfing for days and still I could not find who wrote the equation $c=λν$ for the first time. Neither I found a name for this equation. A lot about Planck's constant and energy related ...
1 vote
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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 ...
310 views

### 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 ...