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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Drag - Dimensional Analysis / Buckingham $\pi$

I'm working on dimensional analysis and I'm having trouble. Here's a problem from my book I'm working on. I'm supposed to consider a small sphere experiencing acceleration due to gravity $g$. The ...
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969 views

Variables in calculation of drag coefficient

Okay, so I looked up drag force equation, and I found that the equation involved the drag coefficient. Then I looked up the drag coefficient, and the equation for it involved the drag force. ...
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Dominant component of drag in a streamlined body (sounding rocket) at 0.8 Mach

We are currently working on CFD solutions on ANSYS Fluent for the drag on our sounding rocket. We are modeling its drag profile through out its velocity range. We currently hit a top speed of approx ...
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365 views

Torque due to air resistance on a frisbee

In my analytical mechanics course we worked out an example involving a disk (say, a frisbee) rotating after being thrown into the air. The disk experiences a torque proportional to its angular ...
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3answers
2k views

Projectile, air resistance and wind

So for my school project I am working on a projectile simulator and air resistance. So I have looked at this. Equations for an object moving linearly but with air resistance taken into account? ...
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1answer
632 views

Explaining the shape of a raindrop and a drop of mercury

I saw on wikipedia that the shape of a raindrop is explained by using Laplace pressure. But why? Since the drop is in motion, we shouldn't be able to use an hydrostatic law, am I wrong? The ...
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48 views

Drag and lift as a function of speed

Assuming turbulent flow, the drag force $F_\mathrm d$ and the lift force $F_\mathrm l$ are usually given in terms of the following equations $$ F_d\, =\, \tfrac12\, \rho\, u^2\, c_d\, A $$ $$ F_l\, =\...
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1answer
98 views

Determine initial velocity of an object which was thrown (WITH air resistance)

I have the following problem: I want to determine the initial velocity of an object which is for example dropped from a moving plane. I know the position, from where the object is dropped and I know ...
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1answer
99 views

Aeronautical Physics induced drag direction

I am a 9th grader doing a science fair project at my local high school. I am doing a science experiment on different plane wings and how the angle of attack affects drag. I need to create a rig to ...
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459 views

What is wrong with this downforce calculcation?

I tried calculating the downforce of a spoiler I need for a robot. I used this formula. $$F = \frac{1}{2}Ac_a\rho v^2$$ Where $\rho$ is air density, $v$ is the speed of my robot, $c_a$ is the lift ...
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579 views

Why did increasing the Ackermann geometry in my race car make it faster in corners?

Ackermann geometry is used to account for the different radius arcs that the front tires follow when the steering wheel is turned from center. It's often expressed as a percentage: e.g. 25% Ackermann, ...
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2answers
69 views

Does air resistance have a greater affect on longer pendulums than shorter ones due to the greater exposure it has to air?

I'm thinking, because longer pendulums travel for a greater time period through the medium of air, air resistance will have a greater affect on the pendulum bob (and string) and so the angle the ...
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1answer
997 views

What is the drag coefficient of an open wedge?

To check my two dimensional CFD calculation I am looking for reference data on the drag coefficient of an open wedge. The geometry is shown below, together with the flow direction. I have found ...
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31 views

Air drag on moving air

Assuming we have a $0.6\ \mathrm m$ diameter fan blowing $3\ \mathrm{m/s}$ as measured by an anemometer at the exact exit of the fan (it was actually measured at the entrance), what is the speed of ...
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1answer
22 views

Formula for deceleration of a car with transmission disengaged

Related to this answer to a question about the speed of an accelerating car, I'm looking for a formula for the speed of a car decelerating in neutral (with the transmission disengaged, i.e. no torque, ...
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1answer
55 views

How to choose the characteristic length in Reynolds number formula?

If we have a car of length $L$ and a simple cuboid of the same length $L$, and assuming both objects are moving at the same velocity, does it mean the Reynolds number will be the same in both the ...
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2answers
72 views

Problem involving the 4 forces that maintain an airplane in level flight

The 4 forces affecting an airplane in level flight are gravity, lift, thrust, and drag. By altering one, the others are affected. My question is could a wing (retractable) be installed on top of a ...
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49 views

Good resource for Drag Coefficient vs Reynolds number (various shapes)?

The Wikipedia page on Drag Coefficient has a nice chart a little way down that shows the Drag Coefficient vs Reynolds number for a sphere, derived from experimental data. I am interested in looking at ...
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54 views

How does this toilet lid work?

After further reflection after closing the lid on my toilet, I noticed it exhibited a behaviour that I can't explain. When you let the lid fall, it falls at a constant speed regardless of its angle. ...
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43 views

Friction at high speeds

I am reading a book which mentions that frictional force is not exactly proportional to the normal force at high speeds. Quoting: Once the bodies slip on each other frictional force is, $kN$. This ...
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1answer
62 views

Calculate the kinetic friction velocity vector from the kinetic friction force in a simulation

I am doing (programming) a simple kinematic 2D simulation on blocks. The idea is that the block will have a force applied. 1) From the force and mass I calculate the the acceleration vector (will ...
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29 views

Individual air molecule momentum exchange

Background: Looking at this illustration about solar radiation pressure on a perfect reflective surface, incident photon exchanges its momentum to the slanted surface which provides a reaction force ...
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26 views

Viscosity from terminal settling velocity of a sphere

I don't have an attempted answer to this question because I don't really know where to start. The Tip says to start from a force balance for the sphere, but I'm not sure on how to do that. I know ...
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147 views

Does cross-sectional area affect the air time of a vertically thrown object?

Factoring in air resistance, I have two objects A and B of identical mass, however have different cross-sectional areas. A has a larger cross-sectional area than B. If I throw both objects directly ...
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27 views

Force applied by horizontal wind on object

Hello, I have a question for a project I'm currently doing: In a tunnel with no gravity, there is a constant wind blowing through. A sphere in the middle of the tunnel is completely motionless to ...
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61 views

How to calculate drag caused by string?

An example - I throw a tennis ball with a short string hanging off one side. As the ball flies the string is dragged to the side opposite the direction of the ball's velocity vector, anchoring the ...
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52 views

Rotational Motion, Kinematics, Air Resistance

When a body is thrown of height in a practical situation ( air is present ) considering air resistance is applying constant opposite force, we could calculate its speed by calculating acceleration ...
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40 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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2answers
119 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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44 views

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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2answers
49 views

air pressure to assist lift on a Race boat

We have a 25 ft race hull with Jet drive pump (we race 30+ mile legs), we are hitting sppeds @150mph. lowering the hydronic drag is a challenge, i am thinking about installing a air injection system ...
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1answer
63 views

Linear motion equation with intital velocity and water drag

at the start i want to mention that i am from germany, so my english is not the best! For a boat simultaion project i am working linear motion equation with intital velocity and water drag. For ...
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311 views

Emperically Determining Terminal Velocity of a Sphere Falling over Critical Mach Number

I originally thought that the terminal velocity of a smooth sphere in free fall through the atmosphere would be an easy question to answer. But for heavy spheres of small diameter, the terminal ...
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26 views

Are the end velocities of masses (falling from infinity to earth) with equal $\rho$ and arbitrary form , scale independent?

Yesterday I asked a question I didn't intend to ask. Of course, masses with different forms (and equal $\rho$) do not reach the same end velocity when falling on earth from infinity. What I meant to ...
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85 views

How to calculate lift and drag of a non-standard aerodynamic body

It is my understanding that the standard method to calculate the lift and drag characteristics of an airfoil is to use formulae and existing data of its coefficients of lift ($C_l$) and drag ($C_d$). ...
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135 views

Effect of atmospheric drag on earth's rotation

Okay, so I had a question answered regarding the earth rotating and planes flying east and west but one part of the answer talked about how the atmosphere is moving along with the earth (same angular ...
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37 views

Feasiblity of a long spinning top using an electromagnet to pull on Earth's magnetic field

Would it be feasible to build a infinitely spinning top (ref. Inception) by including a battery powered electromagnet who's polarity flipped in sync with the top's rotation such that the pull against ...
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471 views

Drag Force on a cylinder with its long axis aligned with the flow

yesterday I started looking into equations that link a cylinders diameter $r$ and length $L$ to the force experienced in a highly viscous medium ($Re<<1$). I found the onseen-approximation but ...
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124 views

Approximation for rotational drag on a box?

The drag equation gives us an approximation for the drag on an object caused by its velocity in a fluid: $F = \frac{1}{2} \rho A v^2 C_d$ Is there any similar approximation for the rotational drag ...
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2answers
72 views

What are the major differences in group-skydiving as opposed to “single” skydiving?

Surface area/the cross-sectional area is greatly increased, so my thinking is it should decrease terminal velocity as well as a couple of other factors. But mass changes too (since there would be more ...
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121 views

Wind resistance on moving body

Suppose that a vehicle is traveling 60 km/h north, and the wind speed is also 60 km/h going the same direction, would there be wind resistance, and to what extent? Also, if I put my hand outside the ...
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702 views

Max speed as a function of engine power

My question started out as finding the maximum speed of a go kart, taking into account only the drag forces as force opposing the motor. I've done some investigation to find: $$ F_{drag}=\; \frac{\...
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312 views

Finding Time & Required Angle for Projectile Motion with Quadratic Air Resistance

This is a physics/calculus/computer science problem, but I think I'll get better results in the Physics SE. I have a fun little project I've been working on (hobby, not homework/production), that ...
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2answers
37 views

How does the width or depth of a container of water affects the speed of an object (e.g. a toy boat) travelling on it?

I am planning to carry out an experiment to investigate how the distance between an object travelling on water (i.e. a toy boat) and the walls would affect its speed. I predict that the speed will ...
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How to calculate the elapsed time while reaching the limit speed?

(Figure drawings belong to me.) In the figure, a person falls freely from the tower at a height of $1500\ m$. When the limit reaches speed, it opens its parachute. By the way, how do we calculate the ...
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1answer
15 views

How would the air pressure inside the hyper loop affect the acceleration of the cabin?

I would like to ask a question about hyperloop's inner air pressure, how would air pressure inside the semi-vacuum tube affect the acceleration of the cabin? Is there any functions or equations to ...
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29 views

Power required to reach X velocity in X time with drag

I wrote a program that adds force to a car like so: Engine Force = Power / Velocity​ Drag Force = -Velocity²​ Net Force = Engine Force - Drag Force = Power / Velocity - Velocity²​ I'd like to ...
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1answer
24 views

Velocity of object on extremely low air density?

If we derive velocity in air when setting air resistance to $kv$, we'll get $$v= \frac{mg}{k}\left(1-e^{\frac{kt}{m}}\right) $$ and if air density goes to $0$, $k$ will also goes to $0$. When $t=T$ (...
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Does the shape of the pipe (the length not the cross section area) affect resistive force?

Does the shape of the pipe (the length not the cross section area) affect resistive force acting on water? Does keeping the pipe straight or keeping it in curves folded over each other effect the ...
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Question about several details in the theory of “Taylor column”

My question refers to a remerkable phenomenon in fluid mechanics, in which flow velocities in a rotating tank of fluid (flow velocity is measured relative to a frame of reference that is rotating ...