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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96 views

Why is $mg = bv$ and not $mg = -bv$?

I was given two formulas, $$F_D = -bv $$ $$F_D = -bv^2 $$ and was told that at terminal velocity, $$v = \frac{mg}{b} $$ which implies that $$mg = bv$$ $$mg + (-bv)=0$$ $$mg + F_D = 0$$ From ...
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Why wouldn't the weight of an object affect the magnitude of the drag force on that object?

I ran into trouble again with a course about drag force on skiing. This is the question, and its explanation: Which of the following factors would not affect the magnitude of the drag force on an ...
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51 views

Damped oscillations and generalized friction

I'm reading damped oscillations from the book Classical Mechanics by Landau and Lifshitz, quoting from the text - "There exists, however a class of problems where motion in medium can be ...
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33 views

Drag calculation from pressure + shear stress distribution

If I know the shape of a body, pressure and shear stress distribution over it, how can I calculate the total drag acting on it ? More exactly, can I calculate it this way: Drag = [Pressure difference ...
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4answers
105 views

Why is it much more difficult to horizontally throw a toy balloon than a football?

If you horizontally throw a sphere of radius $R$ it will feel, in this direction, a drag force due to air. Assume the drag is given by Stokes law, $F_D=6\pi\eta R v$, where $\eta$ is the air viscosity ...
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27 views

Effect of Bodyform on Air Resistance [duplicate]

Visualize those little pictures as the front of vehicles like airplanes and trains. I wonder if I am right about my speculation below, and if so, if somebody could explain the exact reason. Sources ...
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106 views

Sign problem in projectile with drag

So recently, I've been playing around with the variables in projectile motion with drag to see how the trajectory changes. I had my ODE and solved it using separation of variables but the equation ...
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Drag force equals weight

we are doing lab in mechanics class.The task is find terminal velocity of drop of coffee filter and drag force 's constant $B$ in graphically as equation like $mg = Bv^2$ so basically drag force ...
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How could I integrate the changing location of the midpoint of a streamlined body into either the drag or reynolds number?

Because the volume and surface area is constant I am not sure how to represent the change in flow dynamics - laminar to turbulent. (sorry if this is a stupid question, I am a biologist and I can't ...
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50 views

Why do we use $m\frac{dv}{dy} = -b(v-v_{ter})$ while determining how the terminal velocity is changing for an object falls down in linear drag force?

Why do we use $$m\frac{dv}{dy} = -b(v-v_{ter} )$$ while determining how the terminal velocity is changing for an object falls down in linear drag force . I was Jr Taylor's classical mechanics. In the ...
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Kinematics of a body in movement with air drag

Let's assume i got this body (red one) wich is moving along the x-axis. It has got two forces on it, one called $F$, which is constant, and the other called $D$ which is the drag caused by the air ...
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Why is the polar diagram of an airplane depended on weight?

Can anybody answer this question? Although aviation-related, it is in fact a fluid mechanics problem: https://aviation.stackexchange.com/questions/54192/why-is-polar-curve-of-a-glider-dependent-on-...
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29 views

What is the resistance of an object travelling through static fluid at different pressures?

I'm interested in the resistance a body feels as it travels through a static fluid in a tube (of a fixed radius), at different pressures. I would assume that as the pressure is reduced, the ...
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47 views

For a fluid travelling in a tube, if the pressure is decreased at a constant temperature, how does it affect the velocity and fluid density?

I am interested in understanding the relationship between pressure and velocity, as well as pressure and fluid density. I know that the principle of Bernoulli states that there exists a relationship ...
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317 views

Work done by air resistance

How can air resistance do work on a freely falling body on earth. then it's displacement is only due to gravity. I think Air resistance doesn't displace the body falling. So what is the meaning of ...
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106 views

Determine velocity of balloon from known Buoyancy, mass and surface [closed]

I need to know how to get velocity of weather balloon, if I know it's buoyancy force, mass and surface(diameter). I am using now $$v = 0.5t\left(\frac{F_\text{all}}{m}\right),$$ [$m$ = mass, $v$ = ...
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Questions about shapes and the reason behind the drag coefficient differences

What is the reason that a streamlined body has a drag coefficient that is lesser than the drag coefficient of a streamlined half-body, when the latter has a completely flat bottom, while the former ...
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105 views

How significant is the material in drag force calculations?

I went to Wolfram's "Drag Force Calculator" and received 4900 newtons for a cone that has a radius of 3 meters and a height of 3 meters, moving through air at a standard pressure, 15 celsius, at a ...
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1answer
35 views

Units caculation in the article don't match for reynolds numbers higher than 1

The article discusses the forces acting on a falling object in respect to the drag forces and reynolds numbers. The article suggests for varying Reynolds numbers, the force of drag equation is written ...
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Non-dimensional flux

My book states that when a flow around object is considered, Non dimensional momentum flux is defined as the drag coefficient In case of flow through tubes it states The non dimensional ...
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118 views

Would a spring ever stop?

It is not difficult to show from Newton's second law $$m\ddot x = -kx - b\dot x $$ that an underdamped spring has the equation of motion quantified by $$x(t) = c_1e^{-\beta t}\sin\left(\omega t\right) ...
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Moving a marble in a maze using wind force

For a school assignment, I have to write a game where you can move a ball through a maze by generating unidirectional wind when the mouse is clicked. The ball is on a flat surface. The concept is ...
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Air resistance - smooth vs pimples vs dimples

Is there any difference in behaviour between a smooth surface, surface with dimples (dips) and surface with pimples (bumps) when considering aerodynamic drag in a non-rotating frame? I have a flat ...
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1answer
241 views

What does this imaginary number mean for time and velocity? [closed]

As some have pointed out in the chat, perhaps the question that I should have asked is, am I really integrating for velocity? My integration might be misleading in that it integrates for something but ...
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376 views

How to calculate impact speed of a wrecking ball?

So I want to calculate the impact speed of a wrecking ball. I know that I can do that using potential and kinetic energy and the height it was swung from... but that does not account for the air ...
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165 views

Estimating the viscous drag of a moving floating body

I am interested in the viscous drag of a floating body (let's say an cylindrical iceberg in water) moving with a constant velocity, s.t. the Reynolds number of the fluid is very large. I am taking a ...
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221 views

Is the terminal velocity in air independent of the direction of the movement?

For example, a body in free fall on earth and the same body experiencing the same acceleration ($ g $ in this case) but horizontally, would have the same terminal velocity? (considering that the ...
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426 views

Linear or Quadratic Air Resistance

I'm trying to model a rocket's position with air resistance as a factor. The rocket is fairly low-powered (Estes A8-3, 9.7N of thrust for 0.7 seconds), and I estimate it won't be going faster than 50 ...
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Stokes's law proportionality to radius

Is there a logical explanation why Stokes's drag $F_d=6\pi R \eta v$ is proportional to the radius, $R$ of the sphere? Naively I would have expected that it is proportional to the cross section, i....
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“If an object was dropped into water from two different heights, so that it doesn't hit the bottom, would the terminal velocity be different?”

If an object was dropped into water from two different heights, assuming that it doesn't hit the bottom, would the terminal velocity be different?". Suppose that container has a lot of depth that it ...
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In the following path what will be the easier path to ride a cycle?

among the two paths what will be the easier path to ride cycle. Riding it in an overhead bridge by pedaling when going up and letting cycle free when coming down. riding it on a flat road and ...
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Terminal velocity equation for falling skydiver doesn't work for empirically determined values

Try as I might, using the terminal velocity equation with empirically-determined $v_{T}$ and $C_{d}$ requires a skydiver to have a very small projected surface area. I'm not sure what I am doing ...
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AC square wave currents across resistor (no capacitor, no inductor) and gravity air resistance analogy

Update edit: my question is really does alternating electric current through a simple resistor have a mass-based inertia that introduces lag if the frequency of oscillation is high enough? Are there ...
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Why when opening parachute, the man doesn't go upwards?

If an object is moving at terminal velocity and then opens the parachute, the air resistance is higher than the weight so why doesnt he go upwards.
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Aerodynamics of wet versus dry sail

I recently read in a history book that sailing ships that really needed to go fast would pour water on their sails because "wet sails capture the wind better than dry sails." Why might this be? Does ...
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Coefficient of friction between 2 surfaces [duplicate]

If I have both the kinetic and static coefficients of friction between cardboard and steel and between rubber and steel (for the same steel in both cases), is there a way to find the coefficient ...
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1answer
43 views

Does a spaceship heat up if frictional force acts on it?

I was doing a homework question: The answer that I have pasted in the box is the given answer. I understand that the total energy of the spaceship decreases as it experiences friction, and as a ...
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1answer
229 views

Drag Force VS Stoke's Force

Drag force reads $$F_d = \frac{1}{2}\rho_F v^2 \mathcal{C} A$$ Where the letters have the usual meaning (respectively: fluid density, velocity relative to the fluid, drag coefficient, front area of ...
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Will component of force help the rock to move in the same velocity?

Suppose I am on the moon. So I am throwing a rock upwards in a velocity of $v$ with an angle of $a$ with the ground. Now we can divide the velocity in two components. One is perpendicular to the ...
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Impact of spacing between rectangular objects on wind force magnitude

Let's say we place an immovable rectangular object of an area X perpendicularly to a constant wind flow. The wind will now affect it with some force F. Now we split that rectangular object into 4 ...
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Airfoil down force measurement

I have an airfoil connected to two supporting uprights, and each upright has a load cell to the front and to the back, between the bottom of the uprights and a test mount surface. From this system I ...
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Can air resistence force be orthogonal to the velocity?

I wonder if it possible if an object that moves in the air, can generate air resistance that is constantly orthogonal to its movement (and therefore to its velocity).
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Gravitation (satellite around earth)

When a satellite in a circular orbit around the earth enters the atmospheric region it encounters small air resistance to its motion. Then it's said its kinetic energy decreases. But I can't ...
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131 views

How long could someone survive in free fall? [closed]

If there was hypothetically a bottomless pit (no ground), then approximately how far down could you possibly survive without being killed by the speed? (there is no vacuum so air resistance matters.)
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What is the shape of a rain water drop and how it forms? [duplicate]

What is the shape of a rain water drop and how it forms? When tried to figure that out using surface tension, water drop becomes unnatural. Lower part has a smaller radius and upper part has a larger ...
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Question about aerodynamic drag

It is a problem about aerodynaic drag. The following is the formula. $d{\vec{f_{drag}}} = -0.5C_{D}{\rho}{V^2}{({\hat{n_{i}}}\boldsymbol{\cdot}{\hat{v})}{\hat{v}}dA_{i}}$ ${\vec{T_{drag}}}=\int{\...
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What factors determine the coefficient of friction?

I am doing a physics class online, and have a test next week and it is pretty hard to understand a physics class when you do not have the privilege of asking questions as often as i would like. So i ...
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Is the drag force on a thrown object higher in hot or cold air?

Increased temperature lowers viscosity of gases like air but also decreases density. So then drag force would be lower if an object is thrown in higher temperatures but what about viscosity? I thought ...
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Is drag coefficient in fluid dynamics a constant in every direction?

I am referring the book 'Stochastic Processes in Cell Biology'. In this book the author says that Fokker Plank equation in isotropic diffusion: $$\frac{\partial p(x,t)}{\partial t}=-\frac{F}{\gamma}\...
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What is the Davis Equation and why is it used in a Train Simulator?

I have been trying to understand how Microsoft Train Simulator works and people seem to use some Davis equation to calculate friction. So my questions are: What is it? Why do they use it? Are there ...