# 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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### Is there any way to get around the rule that drag $\propto v^2$?

I was looking at a question on aviation.stackexchange and an interesting answer I found included that even today, we have no physical way to get around the fact that drag of a body is roughly the ...
1answer
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### Does the drag force equation hold for an air speed of 475 m/s?

I'd like to calculate the force of drag on a small plate when high speed air is coming into contact with it. I understand the force of drag equation is: $$F = {1\over2}\rho v^2C_dA$$ for $\rho$ = ...
1answer
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### Trajectory of a person from plane to land [closed]

I had a very adventurous dream last night. I was jumping from an aeroplane to save myself from the bomb that was to explode in 2 minutes. Well it couldn't make it. I am trying to get a small formula ...
0answers
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### Why arrow stays tangent to its trajectory? [duplicate]

I'm making custom game engine, with custom physics simulation. I ran into a problem while trying to simulate arrows. Here is what I got for now: The problem is, I don't understand clearly why arrows ...
2answers
428 views

### Finding Terminal Velocity using Newton's Second Law & Stokes Law [closed]

I've been told the terminal velocity of an small spherical object falling through a fluid can be found using this equation: $$v = \frac{2r^2g(\rho_s - \rho_f)}{9\eta}$$ where $\rho_s$ is the ...
1answer
62 views

### What is the time of flight of an object thrown at an angle from the ground with resistive force proportional to the velocity? [closed]

I've been trying to solve a problem recently: An object with mass $m$ is thrown at the angle $\alpha$ from the ground with initial velocity $v_0$. At the point of impact vertical projection of ...
1answer
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### What is wrong with my model of aerodynamic drag?

I am creating a JavaScript program which simulates fireworks in a 2-dimentional context launching from the ground and exploding somewhere in mid-air. The program takes into account gravity and drag, ...
1answer
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### Why the does drag force in the $x$-direction depend on the drag force in the $y$-direction?

If we assume the drag force is quadratic, that is, $\vec{F_{d}} \propto v^2 \hat{v}$, then $F_x \propto (v_x^2 + v_y^2).$ My question is not why this happens mathematically, but rather, why does it ...
2answers
64 views

### Force of Friction and Drag together [closed]

Q : A car is accelerating to the right from a stop. Identify all forces and draw a free body diagram. It is required to use both "Force of friction on car" and "Drag". I am addressing this comment ...
1answer
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### Direction of Drag Force when coming down a steep road [closed]

If a car is moving down a steep road, and we are allowed to ignore friction but not air resistance, which direction is the drag? For example in the image, the drag is opposite of the motion of the ...
1answer
64 views

### Speed of Bubble in Coke

I was trying to solve the following problem, but my results seem illogical when I graph my solution. Assuming we have a bubble at the end of a coke glass, I want to solve for the speed of the bubble ...
0answers
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### What is the air resistance for objects moving supersonically? [duplicate]

A common expression for hydrodynamic drag is a a force that goes $\propto -k v^2$. Physically I have alwasys interpreted this as being related to the ram pressure $\propto \rho v^2$, i.e. for an ...
0answers
29 views

### If a satellite performs an reentry, how does its speed vary?

If a satellite were to leave the Earth's orbit and perform a reentry with no parachutes or rockets to slow it down, how does its speed vary? I know that from equations, as orbital radius decreases, ...
5answers
786 views

### If there was no air resistance, would a car have constant acceleration with constant air/gas input?

To get from 0 to 50 m/s takes a certain amount of force. To get from 50 to 100 takes equal force over equal time, but takes more energy, so would it take more gas input for the second half, meaning ...
1answer
169 views

### How can cats survive a 32 floor fall? [closed]

There have been instances where cats fall from more than 30 stories high, yet escape alive! The record was a cat which fell 32 floors, yet only suffered only slight damage to its body and lost a ...
10answers
25k views

### Why do spaceships heat up when entering earth but not when exiting?

Recently I read up on spacecrafts entering earth using a heat shield. However, when exiting the Earth's atmosphere, it does not heat up, so it does not need a heat shield at that point of time yet. ...
2answers
748 views

### Falling book and paper

I've seen an experiment where a closed book with a piece of paper lying on its cover is dropped a short distance (the piece of paper is smaller than the book; the book's cover is parallel to the Earth'...
2answers
151 views

### Velocity of a body in free fall [closed]

Is it true that the velocity of a body in free fall keep increasing for some time and then becomes constant? If yes,then can we say that the net acceleration, $a=0$ as the velocity is constant? Also ...
1answer
790 views

### Can a car's rims affect aerodynamic efficiency?

Can the rims of a car affect the aerodynamic efficiency of a vehicle? More specifically, is there a difference between rims that are closed, with no holes, and rims that have thin spokes, or rims ...
2answers
44 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 ...
1answer
24 views

### Simple estimate so see if air drag matters

When I create a projectile motion problem for students (in a course where air drag is neglected) I usually solve the problem numerically including drag. Then I plot the trajectory and compare it with ...
1answer
48 views

### Dragged fall before reaching terminal velocity

Consider two objects A and B (of the same shape and size) in fall with air resistance. Object A is much heavier than B. I learned that since object A has a higher terminal velocity it reaches the ...
3answers
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### What lands first a bullet shot or dropped

I think that when you shoot it, it will land later because since the earth is round wherever it land will be slightly lower than were the dropped one landed. So why do they say they will land at the ...
1answer
97 views

### Air Resistance Effects on a Potato, a Dirt Clod, and a Rock

Let me preface this by saying that I know little to nothing about physics, so I understand any personal attacks on my intelligence and gladly accept them so long as I learn something. Having said ...
2answers
664 views

### Why does the mass of an object attached to a pendulum affect the damping?

I tested this out on a simulation (Algodoo) and found that a pendulum with a more massive object attached to it has a lower damping on its velocity. Why does this happen?
1answer
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### Effect of mass on terminal velocity

How does increasing the mass of heavy and light objects affect their terminal velocity in viscous and inertial drag?
2answers
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### Does Stoke's drag formula apply even in the absence of flow?

I know that Stoke's flow (creeping flow) applies in the presence of low Reynold's number situations, i.e. $Re<<1$, which results in the following formula for the drag coefficient of a spherical ...
1answer
193 views

### Backpressure in microfluidic devices

I am fairly knew to microfluidic and i'm trying to get a better understanding of backpressure in such devices. So far, my understanding is that backpressure originates from viscous drag with the wall ...
1answer
93 views

### Why do (short) strands of hair keep a horizontal position while falling?

When I drop a short (5 to 10 cm) strand of hair, it tends to end up falling slowly down at a horizontal position. I would expect a uniform cylinder to fall through air neutrally (at a arbitrary ...
1answer
139 views

### Why darts have feathers?

I have read that feathers stabilize the trajectory of a dart but I haven't found any description how they do this. Any link or comment would be very welcome
1answer
133 views

### At which speed an object becomes hotter as it travels through the air? [duplicate]

Imagine we throw a hot pie at somebody's mug. By the time it arrives at destination, it became slightly less hot. Imagine Chelyabinsk meteor enters the atmosphere. It's cold when it enters yet it ...
1answer
27 views

### Would golf ball with only half hemisphere filled with dimples self correct itself?

Imagine a golf ball with one hemisphere covered with dimples and the other half hemisphere is smooth. Suppose I launch the same golf ball at random orientation into the air numerous time, would the ...
4answers
437 views

### Would a projectile (arrow, bullet) with holes drilled in its length be faster and have greater range?

If any arrow tip or the round of a gun had holes drilled from the front pointy part through the back would it help? It would be lighter for sure. For an arrow you could just fire a hollow tube with a ...
3answers
1k views

### Would a spinning object like a fan stop faster in a non-gravity environment?

Let's say there is a fan spinning and stops in exactly 1 minute on earth. Would it stop faster or slower or exactly same time in a spacecraft without gravity but exact same density of air. Btw: let's ...
1answer
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### 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 ...
2answers
6k views

### Is friction higher or lower in laminar vs turbulent boundary layer?

Is friction drag more or less in laminar boundary layer vs turbulent boundary layer? It is written in this page of wikipedia: The laminar boundary is a very smooth flow, while the turbulent ...
3answers
3k views

### If I shoot into a hurricane, can the bullet come back and hit me?

Are the winds strong enough to turn a bullet around and launch it back towards me? I'm (incorrectly) assuming there's no debris to bounce off of; I just want to know if the winds are strong enough.
1answer
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### Based on Newton's second law of motion [closed]

Why different acceleration are produced in different bodies of same mass but different size?
3answers
270 views

### Magnus effect: Where is the energy coming from?

I am not an expert in Physics, so please go easy on me. The magnus effect creates a perpendicular force to the axis an object spins around and the velocity vector. But where does that energy come from?...
1answer
60 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 ...
3answers
509 views

### Minimum velocity of projectile with air resistance not at top?

Suppose I have a projectile motion without friction, the minimum velocity is always at the top. Now I read that with friction the minimum velocity is not always at the top? Is this true? If yes, why?
2answers
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### How much wind velocity is required to lift a sphere?

What is the math on how much wind speed is required to lift a given mass in a vertical wind tunnel, assuming a spherical object?
1answer
151 views

### Drag force on a sphere [closed]

A sphere of mass $M$ and radius $R$ moves with speed $V$ through a region of space that contains particles of mass $m$ that are at rest. There are $n$ of these particles per unit volume. Assume $m$ is ...
1answer
747 views

### Supercavitation in air

Note: This is a question ask asking for things that might theoretically be possible in the "near future" Project Thor is pretty much dropping 8 ton tungsten spears on things. One of the problems is ...
1answer
48 views

### When an object is moving, does air resistance build up after it begins to move or during?

For example,if a car is accelerating to 70km/h, when the car is at 35km/h, will air resistance also be at 35km/h or will it slowly build up after it begins accelerating?
1answer
296 views

### Vertical motion with air resistance [closed]

I have an arbitrary object with initial velocity $v_1$ pointing upwards. There's also air resistance proportional to the square of speed. So this object goes up, turns around, goes back down and lands ...
1answer
499 views

### Bullet drop uphill and downhill [closed]

I have been trying to figure out why a bullet seems to drop less quickly over the same distance when shot uphill or downhill (i.e. not parellel to the earth's surface), and can't wrap my head around ...
1answer
93 views

### Skier maximum speed [closed]

Assume no sliding resistance. But include wind resistance. Angle from 0 to 90. A vertical slope is fair. What angle would produce the maximum speed. I know 90 vertical seems the obvious but less ...
2answers
118 views

### Center of gravity for best in-flight behavior of oblong projectile

I am interested in improving the in-flight behavior of an oblong projectile that is launched from something like a trebuchet (a rotating arm).* This is a hobby project and I'm not an engineer or ...
2answers
374 views

### Deriving velocity as a function of displacement from ({velocity, displacement} as functions of time)

I have been trying to solve this problem for a while to no avail. Suppose we have $$m\frac{dv}{dt}=mg-bv\enspace,\qquad v(0)=v_0$$ (Where, of course, $m$ is mass, $g$ and $b$ are constants.) We ...