# Questions tagged [velocity]

The time rate of change of the position of an object

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### Confusion on higher derivatives of position [closed]

If I apply a force to a stable object and it moves, the resultant force is $>0$ (Newton 2nd law). Ignore any frictional forces: acceleration occurs and changes from $0$ to something $>0$ say in ...
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### Why do things stop accelerating?

Before $t=0$: object is not moving At $t=0$: I push object with sufficient force to overcome static friction After $t=0$: Object accelerates. Resultant force is greater than $0$. Dynamic friction is ...
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### Dependence of Lorentz factor on only a component of velocity

In cases of two- or three-dimensional space, why doesn't the Lorentz factor of a component of 3-space momentum depend on only the corresponding component of velocity? That is, why isn't there, for ...
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### How is the Rapidity Vector Calculated from Velocity Vector and vice versa in special relativity?

How is the Rapidity Vector calculated from Velocity Vector in 3-D and vice versa in Special Relativity? What I want is to take 2 3D Velocity Vectors, convert each to corresponding 3D Rapidity Vectors, ...
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### Why is the speed of a quantum particle defined as coefficient of $t$ over coefficient of $x$?

I’m currently studying quantum mechanics from Introduction to Quantum Mechanics by Griffiths. In his free particle section, he says that the speed of a particle is the coefficient of $t$ over the ...
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### Motion in one dimension calculating accelaration [closed]

An athlete; Jayleen, starting with an initial velocity of 4m/s; runs with constant acceleration for 6s. Her velocity is measured as 13m/s. What is her acceleration in m/s2?
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### How does the size of a valve opening determine liquid velocity and pressure?

Say we have a water reservoir with a valve near the bottom to allow water to be released into a separate reservoir (for example, in order to avoid flooding). The valve is initially slightly (10%) open,...
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### Why does fluid pressure decrease as fluid velocity increases according to Bernoulli's principle?

I’m studying aerodynamics. I understand Bernoulli’s principle very well, I just can't wrap my head around why pressure decreases as velocity increases. Like the garden hose example: if you cover the ...
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### Can you equate relativistic mass to rest mass? [closed]

I am doing a project with the Inelastic Collison equation and was wondering whether you can insert a relativistic mass into it or whether you can only use rest masses. If you can, is there any ...
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### Changing mass with velocity

I was wondering that a change in velocity can change the mass of an object slightly. I thought of this since p=mv so if we rearrange it to be m=p/v. Does this mean that a change in momentum or ...
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### Find the velocity of $v$ [closed]

In the arrangement shown in the figure the ends P and Q of an inextensible string moves downward with uniform speed u. Pulleys a and b are fixed. The mass M moves upwards with what speed? How can v ...
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### Is $d \mathbf v · d \mathbf v = d \mathit v^2$?

My teacher has proved the following: $$\mathit v^2 = \mathbf v·\mathbf v = \frac{d\mathbf r}{dt}·\frac{d\mathbf r}{dt} = \left(\frac {ds}{dt}\right)^2 \Rightarrow \mathit v = \frac{ds}{dt}$$ Because ...
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### The derivative of the unit velocity vector

The set up: An intertial frame Y-X used to describes trajectory of an insect on some rigid body using some relative vectors. Symbols: $\vec{r_a}$ is is the vector connecting the origin to some point ...
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### Calculating flow rate through a mesh

I want to calculate the flow rate of water through holes in a mesh. In the following hypothetical situation water is flowing through a 13mm diameter pipe at a velocity of 3 meters per second and a ...
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### Why are drag and kinetic energy proportional to velocity squared? [duplicate]

For example, it takes a car four times the kinetic energy to travel the same distance at twice the speed, which quadruples the drag experienced by the car. This observation is described by the ...
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### Would a navigator announcing ship velocity whle approaching lightspeed make linear announcements?

Given my admittedly limited understanding of relativity, I believe that as a hypothetical space ship approaches the speed of light at a constant acceleration, what the crew would "see" on ...
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### What is the effect of the mass of object on its acceleration? On its velocity? [closed]

A short answer will do, thankyou!
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### Why do the two balls come down at the same time?

I saw this video on YouTube in which two balls slide down on different inclines. The part which confused me was the one at 2:00 seconds. I couldn't understand the physical reason for that. If we drop ...
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### Direction of velocity and displacement

Do velocity and displacement always have the same direction? I know this seems like a silly question to ask, but I'm having a hard time coming up with any counter examples, and I'm not able to prove ...
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### Interpreting recession velocity (red / blue shift)

I just had to teach something that I myself have never learned, concerning recessional velocity of galaxies. Awkward! The question was: "A line in a hydrogen spectrum has a wavelength of 486.1nm ...
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### Why do two similar objects not hit the ground at different times?

The formula for air resistance is $$F_{air}=\frac{1}{2}\rho cAv^2$$ where $\rho$ is the density of the air, $c$ is the drag coefficient, $A$ is the cross sectional area of the object and $v$ is the ...
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### Relative Velocity and Mass

Under what conditions can you just add velocities? For example if I throw a paper ball in the air in a 1m/s wind the ball should move in that direction at 1m/s as it falls according to relative ...
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### Needed force to reach specific point for the ball

I am making a billiard game and need to push white ball to move other balls which should pocket so I need to calculate the force. I have mass, friction, distances, angles, collision point, origin ...
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### What is the difference between non-uniform velocity and acceleration?

So I know non-uniform velocity as, "Non-uniform velocity is when an object covers unequal distance in equal interval of time in a particular direction or covers equal distance in equal interval ...