A subset of [tag:fluid-dynamics] concerning primarily forces such as lift and drag generated on bodies as they move through gasses or as gasses move through the body (typically air).

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Could one fire a bullet with sufficient speed to leave the Earth?

Consider a gun or rifle fired directly upwards. My original question was what speed would be required to escape the Earth. The escape velocity from the surface of the Earth is the classic $$v_e = ...
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3answers
70 views

Why does a sheet of paper fall slower than the same when rolled into a ball?

It depends on volume but both the sheet and the sphere have the same volume. Does surface area play any role here?
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2answers
95 views

Pressure-Velocity relation at a point in a flow

How can we relate pressure and velocity at the same point in a fluid flow? Why does pressure decrease with increase in velocity?
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3answers
907 views

Are the hypotheses of the Bernoulli equation satisfied for a bird or airplane wing at low Mach number?

A previous question by David Zaslavsky was a request for a broad, "how things work" type of explanation of the lift of an airfoil. The answers given there are enlightening, but don't address a more ...
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2answers
2k views

What exactly is the 'lift' of a sailboat as explained by Bernoulli principle

I have heard that when a sailboat is sailing against the wind, it operates on the principle of 'lift'. I am unable to understand the explanation, based on Bernoulli principle, completely. My question ...
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6answers
354 views

Why is a beam reach the fastest point of sail on modern sailboats?

I've heard that a beam reach (perpendicular to the wind) is the fastest point of sail on modern sailboats, but I haven't heard a satisfying explanation of the physics behind the claim. Triangular ...
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1answer
69 views

What are the biggest reasons that Cars get higher Land Speed Records than motorcycles'? [closed]

What are the biggest reasons that Cars get higher Land Speed Records than motorcycles'? It is because cars have a more streamlined frame than than motorcycles? But, from pictures, it seems that ...
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10answers
26k views

What really allows airplanes to fly?

What aerodynamic effects actually contribute to producing the lift on an airplane? I know there's a common belief that lift comes from the Bernoulli effect, where air moving over the wings is at ...
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1answer
60 views

What shape has the highest drag coefficient?

This image from NASA illustrates drag coefficients for several shapes: It is generally accepted that some variation of the teardrop/airfoil shape has the lowest drag coefficient. I was wondering ...
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1answer
166 views

Why does a propeller suck in air from the front?

A rotating but fixed propeller sucks in air from the front. What is the cause for this acceleration of air particles? Since propeller blades act like rotating wings, my best guess is that the blades ...
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0answers
16 views

Hard Drive Air Bearing Questions [closed]

I have a few questions related to the physics of the air bearing and head movement in a hard drive. What is the origin of the air bearing between the spinning platters and the head? Is it air ...
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8answers
30k views

Why does the air flow faster over the top of an airfoil?

I understand the common explanation of lift, which describes the airflow over the top of the wing as moving faster than the air below the wing. However, I don't quite understand why the air moves ...
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2answers
854 views

Difference resultant aerodynamics force on an airfoil and a flat plate

From basic airfoil theory the following free body diagram can be determined for a two dimensional asymmetric airfoil: Here the direction of the resultant force is governed by the geometry of the ...
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1answer
3k views

Why, when one opens 1 car window, does that noise occur?

When you're driving and you open 1 car window, say the front one, there comes a horrible noise, but when you open another window just the slightest bit, this noise goes away (I'm sure most people know ...
11
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1answer
224 views

Equation derivation for skipping rocks

oWhy can rocks skip over water? For instance, if you conduct an experiment where you drop both rocks from the same height, but give one considerable acceleration in the x direction, one will fall in ...
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4answers
140 views

How does a converging-diverging nozzle not violate conservation of energy?

Disclaimer: I know absolutely nothing about fluid dynamics, and very little about physics in general. THis may be a really dumb question. Now, at subsonic speeds, converging and diverging nozzles ...
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1answer
143 views

Understanding equation for force acting on stones skipping over water

I think I have a decent conceptual understanding of the forces at work when stones are skipped over water. My question pertains to this equation, $$ F = C_L\rho U^2S\sin({\alpha + \beta}) $$ which ...
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1answer
45 views

How a paper plane(rocket) flies in air? what is science behind it? [closed]

What factors helps a paper plane to fly and can you explain how these factors help the plane to fly?
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0answers
42 views

Magnus effect, Coanda effect, and the Bernoulli principle: What is balancing gravity on a spinning sphere vs. a stationary screwdriver?

I've seen videos of golf balls and screwdrivers levitated by a focused air stream. Reading the comments of these videos (and others), I see explanations of the machanics at work and their cause and ...
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3answers
69 views

Will computer fan rotate slower if one makes impeller heavier?

Imagine that we replace plastic fan impeller with identical metal impeller (same form, heavier weight). Would maximum fan speed decrease? Common sense suggests that air resistance and bearing ...
0
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1answer
73 views

Could a Jumbo Jet aircraft fly on paper wings?

My dad was an airline pilot and, during his training, his instructor told him that, in absolutely ideal conditions, (in practice obviously impossible) that the actual material composing the wing ...
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5answers
1k views

How to sail downwind faster than the wind?

Recently a group set a record for sailing a wind-powered land vehicle directly down wind, and a speed faster than wind speed. Wikipedia has a page talking about it, but it doesn't explain exactly how ...
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3answers
96 views

If gravity were to suddenly change, would the lift generated by a airfoil also change [closed]

If gravity were to suddenly change, would the lift generated by a airfoil also change? I realise that if gravity were to increase, then weight would also increase, leading to a change in the ...
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2answers
64 views

What's wrong with this argument that aerodynamic lift really does rely on Bernoulli? [duplicate]

There is a grade-school explanation of how a wing works that goes approximately like this (although I'm leaving out an erroneous bit): Because of the geometry of the way the wing meets the air, ...
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3answers
129 views

Why are vehicles not pitted like golf balls?

I have read that non-laminar flow reduces drag on blunt bodies. Given that, why is pitting not used on motor vehicles?
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2answers
322 views

Integrating pressure over a surface

Consider the 2D airfoil below. In engineering (and maybe physics) you will often see something like the following as an expression for the pressure force acting on a surface (in this case a curve ...
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0answers
52 views

Question about Elon Musk's Hyperloop Suspension [closed]

So one of the proposed suspension systems that will be used on the hyperloop include the externally pressurised air cushions. These cushions lift (or atleast help lift) the capsule and reduce drag ...
3
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1answer
778 views

Why do vapour cones form around jet fighters?

Apparently this phenomenon has nothing to do with jets breaking the sound barrier and has something to do with the Prandtl-Glauert singularity as described on Wikipedia. But, the Wikipedia article ...
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3answers
47 views

Why do the tangent holes (like in pitot-static tube) feel the static pressure?

Why do the tangent holes (like in pitot-static tube) feel the static pressure although the static pressure is in the direction of the velocity of the streamlines not normal to the surface of the hole
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1answer
45 views

How much does air resistance affect the angular velocity of a golf ball?

I'm modeling the flight trajectory of a golf ball, and using angular velocity to calculate the Magnus force. Currently, I'm assuming angular velocity to be fixed throughout the ball's flight. How ...
4
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1answer
113 views

Why do some (older) wind generators have more than three blades?

Based on my personal observations, newer windmills seem to have three blades while older ones tend to have four or even more. This question has excellent discussion on my three is an optimal number. ...
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1answer
309 views

Could the phenomenon of vortex bursting be exploited to reduce wake turbulence?

One of the classic stories in the annals of aerospace engineering is the development (and subsequent redesign) of the F-18 and its Leading Edge Extensions (LEX) due to fatigue problems, problems that ...
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3answers
482 views

Forces on an aircraft - thrust, lift, drag, weight

I'm extremely sceptical about the wikipedia page on aircraft flight mechanics. When describing 'straight climbing flight', it says: lift is unable to alter the aircraft's potential energy or ...
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3answers
113 views

How laminar or turbulent is air?

Consider an outdoors scenario, with good weather and no sensible air currents at the floor level. How turbulent or laminar is the air surrounding this environment?
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1answer
59 views

Does a ceiling fan sound louder when humidity is higher?

It seemed to me the ceiling fan is making louder noise(of cutting through the air) when the day is a bit damp/humid, especially after a rainy day/hour. Is this a valid observation? Can the increased ...
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3answers
169 views

Why does it seem as if big vehicles “attract” mine when I drive close to them?

When I drive a car at high speed and when I am near to another big car (like a van, or transport vehicle) I feel an attraction to or something push me toward the other big car. What's the physics in ...
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2answers
1k views

Is Magnus effect a corollary of Bernoulli principle?

Magnus effect is commonly explained using Bernoulli principle. However, taking the lift on a rotating cylinder as an example, the velocity difference is caused by the extra work done by the rotating ...
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2answers
96 views

Why bumble bee cannot fly aerodynamically? [duplicate]

I just saw this pic So I got curious and logged in on physics.stack first time, is it true? I am a math major and usually wander on mathstack but I would like to understand why Bumble bee cannot ...
0
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1answer
51 views

Balloon aerodynamics

In this recent anime that I have seen, there is a part where an atomic bomb is sent to the stratosphere in a box, by a helium balloon. As you can see in this picture of the set-up, there is a tube ...
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1answer
41 views

How is the kinetic energy of the wind transferred onto a lift based wind turbine?

The rotor blades of a lift based wind turbine are shaped like airfoils, so the wind flowing around them creates a lift force which in turn moves them around. From a thermodynamic viewpoint and like ...
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3answers
2k views

How do eagles fly slowly for a long time?

Eagles fly slowly for a long time. Many other species fly faster and move their wings faster. But eagles keep their wings steady, and move only their tail. How do they move slowly in the air, ...
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2answers
400 views

Why ballasted gliders fly faster

The fact: Gliders have ballast tanks that can be filled with water. The addition of ballast increases weight, and this allows the glider to fly at faster airspeeds while maintaining the same glide ...
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1answer
70 views

Why don't we build helicopter based space shuttles?

As seen in this video: the principle of the helicopter does work in space. So we could make a helicopter based space shuttle! It would be easier to navigate with it than with propulsors.
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1answer
35 views

Control surface effect

If we know the Center of Mass and the Center of Lift, and the position and rotation of some control surface, how can we calculate what control surface must be operated to change our path? lets say we ...
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4answers
341 views

Why is paper (or any tailless) airplane pitch stable?

To clarify my question further I'll use a practical example. Here is the simplest paper plane design I could think of - it is a rectangular thick drawing paper with a weight attached at the middle of ...
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6answers
3k views

Turning an Airplane. What actually causes the circular motion in a banked (roll) turn?

Basically I'm wondering if this is correct. Which essentially says that you need a torque to get the nose of the craft to turn and that this is provided by the rear tail surfaces. After trying to ...
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1answer
257 views

Why are the backs of airplanes curved?

I get the front part, but why is the back curved too? I do not see a problem with the back being flat.
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1answer
94 views

How does a hovercraft hover, if it has low pressure underneath it?

I've read a few different explanations of how hovercrafts hover, and they all mention a low-pressure cushion of air. This confuses me though: If there is low pressure under the hovercraft, why doesn't ...
2
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1answer
59 views

Reynolds number of airfoil in a pipe

As part of a physics high school paper I am writing, I need to build a wind tunnel. As part of my calculations, it appears that Reynolds number is very relevant in aerodynamics (specifically for ...
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2answers
112 views

Do rotating non-circular projectiles also experience Magnus lift?

The Magnus effect has been studied on spherical projectiles such as golf balls, tennis balls, and soccer balls. The backspin of a golf ball leads to Magnus lift that opposes gravity, thus allowing the ...