Questions tagged [drag]

The force on a body resulting from it's motion through a fluid (gas or liquid). This force is directly opposed to the direction of travel.

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Does (and how) a shark fin on car top (or fan blade) reduce drag?

I've heard this kind of shark fin on the roof reduces drag by breaking the wave that forms behind, where the roof bends into rear window. image source The story goes that it's similar to these fins ...
culebrón's user avatar
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Can sail be fixed or simple aerodynamic shape split?

Is it possible to create small shape that would be aerodynamic in most directions and not much in one of (kind of fixed sail) ? Performed some experiments with pyramid like shape in front of bike (...
Jan's user avatar
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Why are cylinders more aerodynamic than spheres?

Why are cylinders more aerodynamic than spheres? Say you have a cylinder falling vertical that has rounded ends. Now remove the cylinder part. Now you’re left with a sphere but without the skin ...
Wyatt's user avatar
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Rocket attached to a pendulum. How is energy conserved?

I'm trying to wrap my head around a conceptual problem involving a simple pendulum with a rocket attached to its mass. Imagine the rocket expels gas to provide a tangential thrust force. However, the ...
Eduardo González's user avatar
1 vote
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Circular motion with air resistance [closed]

A mass of object M = 100 g is attached to the end of a string of length R = 20 cm. A person swings the mass overhead such that his hand moves in a circle with radius r = 10 cm with angular velocity ω =...
Bik Kuang Min's user avatar
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1 answer
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Time taken for ball to reach down is more? [duplicate]

If we consider a practial situation, where air resistance exists, why does a ball/object take more time to come down than to go up? This seems contradicting to me at the first glance, but I am pretty ...
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How optimal launching angle is affected by mass?

I'm writing a code to calculate the maximum optimal angle for motion under linear drag and how it's affected by mass. It appears that for the most part this angle is independent of mass and not of ...
KatJ11's user avatar
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Would an object stop if the only force acting against it is air friction? [closed]

This question has bothered me for some time couple of years ago, so here is the main problem: Suppose that an object of mass $m$, is thrown with horizontal velocity $v$ on a horizontal, frictionless, ...
CuriousCrypto's user avatar
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In Stoke's law how terminal velocity depending directly proportional to the velocity of object?

In common examples and understanding, like bullet firing, higher the velocity the distance traveled will be higher in a given time, but in the case of terminal velocity concept it is said that the ...
ayyappan muthukrishnan's user avatar
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Maxwell's wheel - moment of inertia vs damping coeff

I am investigating the relationship between the moment of inertia of a yoyo-like apparatus (maxwell's wheel) and its damping coeff. I am adding disks to my yoyo to change its moment of inertia, which ...
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When you put your hand out of a car that is moving you can feel the air, what would it feel like in a vacuum?

Imagine that you could put your hand out of a spaceship whilst it was travelling and it wouldn't get injured. What would the sensation be like? Would you feel anything, or would you not be able to ...
Scarjo's user avatar
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Is air resistance totally dependent on surface area?

Two objects of varying mass, but of the same surface area, are dropped from the same height. Which will strike the ground earlier?
Sarvani's user avatar
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How do I calculate the $v^2$ part of the air resistance $(1/2)CpA$ into constants that will fit my general equation

I am currently working on an applied maths project in which I have modeled the forces at play when a rollercoaster travels down a slope and comes to a stop over a distance $d$ with the use of brakes. ...
Loch S's user avatar
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Stresslet vs hydrodynamic force

I would like to understand all types of forces exerted on a small particle in a Stokes flow. According to this, page 9, "stresslet" and the hydrodynamic force were defined as two different ...
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What is exactly particle inertia in a fluid-particle mixture?

In a mixture of a cylindrical particle and the carrier fluid, what exactly particle inertia refer to? (let's neglect gravitation force and Brownian motion). When the size of particles are small (...
user2966501's user avatar
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Falling through a thixotropic ocean -- what would happen?

Drop a heavy incompressible object into water and it would splash and then presumably reach a certain terminal velocity where acceleration is nill. If you dropped a heavy incompressible object into a ...
Robert Law's user avatar
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Forces exerted from fluid on a particle in Stokes flow

Assume we have some small cylindrical particles near a specific point in a laminar flow, such that the particle Reynolds number is around unity. Neglecting mechanical interactions between particles, ...
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Rocket-assisted drag cancellation in artillery shell

The main limit on artillery range is drag. Hence for the same muzzle velocity, the WWII 800mm Schwerer supergun had twice the range of the modern 155mm M777 gun, because the super shell had a much ...
Abdullah is not an Amalekite's user avatar
3 votes
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Air resistance due to Helium vs Air

I was reading this technical note by NASA on windage power loss in alternators. In the paper, the power loss due to fluid shear between two concentric cylinders (a rotor and a stator) is derived. The ...
E400Jack's user avatar
2 votes
1 answer
108 views

How do you calculate the air friction on a large magnetically levitated ring travelling within a toroidally shaped vacuum enclosure?

For this question, assume... That the inner wall of the enclosure and the surface of the ring are smooth. A high vacuum level, but not a perfect vacuum. Rarified gas density is $\rho$. That the ...
phil1008's user avatar
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Air Friction Newton III

I have question to the Newton III Law and Air Friction. At the free Fall of a Body there is an Air Friction, which is in oppopsite direction to the Gravitation Force. In my opinion the Body pushes to ...
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Contact force to air pressure ratio

Preamble Just to preface, I am not a physicist or physics student. So my question is not related to any real world application or projects. It is more of a shower thought than anything else. Therefore,...
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Does earth revolution speed slowing down because of small drag from space is not empty?

I read that universe is not empty, in least dense parts has 1000 atoms per cubic meter, does that slow down earth speed? Why these atoms are there, why they are not attracted by surrounding gravity ...
user707264's user avatar
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How to mathematically derive the pressure contribution to drag force over a with viscous contribution determined?

I've looked in a lot of books on how it would be possible to derive the drag force over a sphere using PDEs. I've also learned in my fluid dynamics class how to derive the drag force of a rotating ...
Benri's user avatar
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How to mathematically derive the pressure contribution to drag force over a sphere after the viscous stress is determined? [duplicate]

I've looked in a lot of books on how it would be possible to derive the drag force over a sphere using PDEs. I've also learned in my fluid dynamics class how to derive the drag force of a rotating ...
Benri's user avatar
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Why does a bullet precess in the opposite direction from gyroscope diagrams? [duplicate]

I am reposting this because it was not resolved when I first posted. Bullet spin causes a bullet to become a gyroscope. Specifically, bullets have their center of pressure in front of their center of ...
Johnlpmark's user avatar
1 vote
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121 views

Oscillator with non-linear damping / drag equation

For linear damping $$ \ddot{y} + 2\beta_0 \, \dot{y} + \omega_0^2 y = 0 $$ the solution with initial conditions $y(0) = y_0, \; \dot{y}(0) = 0$ reads $$ y(t) = y_0 \, \sec\delta \, e^{-\beta_0 t} \, \...
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Can anyone suggest a calculation model for estimating the location of a dropped object falling from a height?

I'm trying to find models that allow me to calculate dropped objects, specifically, a model where I can consider lateral displacement due to wind force and vary the weight and resistance force of the ...
Francisco Lopez Chamberlain's user avatar
-1 votes
3 answers
61 views

Force exerted by water flowing in a pipe bent into a circular arc

my school teacher told me that when water flows in a pipe, it exerts a force equal to $ρAv^2$ where $ρ$ is density, $A$ area and $v$ velocity. he further said that when the liquid enters the pipe, the ...
Baksish's user avatar
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Friction vs drag/resistance force

we know that friction is a kind of resistance force, so friction should some how related to resistance force, but i just curious why they have different formula indeed. The friction formula is given ...
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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 ...
user136808's user avatar
1 vote
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54 views

3D pendulum with friction [closed]

I'm trying to do a simulation of a spherical pendulum of length $l$ with air drag and I need to solve numerically the second order differential equations of the angles $\theta$ and $\phi$, where $\...
Enrico's user avatar
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2 answers
108 views

Does heavier car need more aerodynamic downforce in turn than lighter car for same cornering speed?

When a car turns, the frictional force $F_f = (mg\mu + A\mu)$, where A is aerodynamic downforce and $\mu$ the friction coefficient, needs to match the centrifugal force $F_c = m \times V^2/r$. If the ...
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Understanding lift on a rotating cylinder (inviscid)

From J.D Andersons Aerodynamics book, under the category of describing inviscid flow (over a rotating cylinder in this case), it states "...the friction between the fluid and the surface of the ...
George kirby's user avatar
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2 answers
65 views

What causes an arrow to rotate? [duplicate]

My intuition: In a system without air resistance, I would expect an arrow shot at an angle with its head pointing upwards to follow a ballistic trajectory without rotating around the horizon - because ...
shaiko's user avatar
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1 answer
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Problem with modelling a water rocket

I am trying to model a water rocket to find the optimal volume of water(without neglecting air resistance). So, firstly, I make the assumption that throughout the journey of the rocket from t = 0 to t(...
user136808's user avatar
0 votes
1 answer
34 views

Dimensional analysis of particle falling against air resistance [closed]

I'm trying to solve a question in a sample exam paper. The student is asked to use dimensional analysis to find the time taken for a particle to fall a certain distance when drag is proportional to ...
Martin CR's user avatar
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1 vote
0 answers
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Theta-Beta-Mach relation for small deflections

I'm currently studying shockwaves, particularly their effects on drag. I've stumbled upon an odd formula in "Elements of Gasdynamics" (Liepman and Roshko, pages 52-53), in there I saw an ...
Mike November's user avatar
0 votes
1 answer
106 views

How can the panel method be used to find drag and lift if it is for invicid flow?

If simple CFD softwear like XFoil and OpenVSP use the panel method to find an estimate of the drags and lifts/pressure distributions. How do they find drag and lift if the panel method works based on ...
George kirby's user avatar
1 vote
1 answer
104 views

3D projectile motion simulator with drag is not constrained to a 2D plane

This is an example of the problem. I've set the initial velocities to be $(x,y,z) = (100,10,100)$ and the drag-coefficient and CS-area to be 1. As you can see the motion is not constrained to one ...
Thenu Kaluarachchi's user avatar
0 votes
1 answer
109 views

Terminal velocity of two raindrops

Question: "Consider a small (less massive) raindrop, and a large (more massive) raindrop (consider both to be spheres), falling with air resistance (drag). Which will have a larger terminal ...
Hecron's user avatar
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0 votes
1 answer
63 views

Can direction of frictional force be opposite to velocity?

The frictional force in incompressible Navier-Stokes equation is given by $$\vec F = \nu \nabla^2\vec v$$ Lets assume simple 1D-flow along $x$, where $v$ depends on $z$: $$v_x = v(z)$$ Then the ...
MichaelW's user avatar
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0 votes
1 answer
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Why is the pressure underneath a car splitter lower than the ambient

I seem to get very mixed answers online but i don’t understand why the underside of a splitter is said to have low pressure, i get that the above pressure is higher relative, but not why the underside ...
George kirby's user avatar
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0 answers
37 views

Why don't they use golf ball dimples on cars? [duplicate]

Just watched an episode of mythbusters where they proved that a car got better fuel economy with golf ball dimples. So why don't they use that on cars?
Derrick Rondeau's user avatar
0 votes
2 answers
150 views

Does car use more fuel when accelerating (for same delta) at higher speeds if resistance forces are constant?

If air and tyre resistance are constant over speed(unrealistic), does car use same time,same total fuel,same fuel/ distance and same fuel/time to accelerate from 100 to 150km/h then from 200 to ...
user78495162's user avatar
1 vote
1 answer
68 views

Signum function and friction

There've been some times where I've seen people including the signum function, $\text{sgn}(v_x)$ in equations of motion to account for the instant when the horitzontal velocity component, $v_x$, ...
Joan S. Guillamet F.'s user avatar
-2 votes
2 answers
127 views

Why Is Wind Energy Velocity Cubed Instead of Squared?

Formula for everything seems to be squared, for example, kinetic energy $KE = \frac{1}{2}mv^2$ But for wind energy, this formula is cubed, e.g. $\frac{1}{2}\rho A v^3$ I couldn't find any results for ...
burner8268's user avatar
1 vote
2 answers
93 views

Air resistance in the Cavendish Experiment

Would air resistance be an issue in the Cavendish experiment or are the velocities so low as to be irrelevant? Could it cause the experiment to fail?
doca's user avatar
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15 votes
1 answer
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In beer, why do bubbles travel faster upwards in the center?

This is a very odd question, but I just so happened to be observing a pint of beer and realized that the bubbles floating up seemed to travel faster towards the center of the glass than towards the ...
Corey Mitchell's user avatar
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0 answers
12 views

Why doesn't the ratio of inertial to viscous forces ($R_e$) depend on the object shape - frontal vs side area?

Why doesn't $R_e$ depend on frontal and side area? - Understanding Reynolds number in the context of varying object geometries. I have not taken a fluid dynamics course, but have been reading up on ...
Cat Sculpture's user avatar

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