# 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 air resistance truly linear in surface area?

Air resistance is generally said to be linear in the surface area of the moving object. Out of pure curiosity, I am wondering to what degree this is an approximation, i.e., when this assumption begins ...
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### Issue with simplifying the equation related to non-uniform acceleration

I am exploring how the cross sectional area of a drogue chute affects its velocity after travelling a set distance. I got this equation: $$m_1 a = m_2 g - \frac12 c_d \rho A v^2,$$ This covers the ...
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### Why rain drops are spherical while water droplets on a glass surface are flat?

Why are raindrops spherical when falling through the air, but lose their spherical shape when they are on a flat surface?
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### Vertical trajectory of a projectile with quadratic drag

I was wondering is there is an equation (or function) that can predict the apogee time and height of an object given its current acceleration and the usual constants ( mass, drag coefficient, cross ...
1 vote
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### Where exactly is the friction with the pipe walls and the fluid? [duplicate]

Is the friction between the walls of the pipe and the no slip layer? Or is it between the no slip layer and the rest of the fluid above?
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### Calculating aerodynamic forces on a random object

I've set out to designing a game that would let the user design a vehicle/plane and then fly it around and I'm interested in what would be the best way to go about the physics aspect of it. The 3d ...
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### General solution for the motion of a 1D particle with drag

Consider a particle of mass $m$, with equation of motion $$m\ddot{x}=-U'(x)-f(\dot{x})\dot{x}.$$ I am trying to find an equation of the form $v=g(x)$ so that we can reduce this to an integral of the ...
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### Is the drag coefficient linear with speed?

I made an RC-car and wanted to simulate the drag of it in Solidworks. But after I did my simulations I put my results in a graph, the drag is quadratic with speed but the drag coefficient $C_D$ is ...
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### How do you convert the damping coefficient to speed dependent drag coefficient (for low speeds)?

I'm trying to understand how to convert the damping coefficent to the speed dependent drag coefficient for an investigation I am doing for school.
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### Resisted vertical projectiles

My textbook writes this equation for the vertical acceleration of a particle undergoing 2D resisted projectile motion (the resistance is linearly proportional to velocity). The situation is simply the ...
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### Why do objects with more mass fall at a faster rate (factoring in air resistance)? [duplicate]

My class had to do an online simulation about the different free fall times of objects, both on Earth and in a vacuum. In it, I noticed that in an atmosphere, objects with greater mass fell faster ...
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### An instrument for sensitive time interval measurements?

I had the idea to do an experiment at home that would let me calculate the air resistance. $F_{net} = m.a = m.g - f_k$ (kinetic friction), in the case of free fall, so I thought I’d drop an object of ...
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### Does drag coefficient vary with size?

Take three spheres having respectively a 1 meter, 100 meters and 1000 meters diameter. Size aside they don’t differ in any other way. They’re moving through a fluid at the same, constant velocity of 3 ...
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### Movement of a mass on a spring in damped SHM

Suppose a ball is connected to a spring attached to a wall, and they are in space, i.e. assume no gravity. The ball is put into a fluid with Stoke's drag and oscillates backwards and forwards relative ...
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### Difference between Drag force and virtual force

When an object submerged in a flowing fluid, it will experience a drag force due to shear stress and pressure. Now, I read that there is something called "virtual force" as well acting on ...
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### Parabolic(?) projectile orbits as an approximation to elliptical orbits given a rotating Earth

Why is projectile motion a parabola given that the Earth rotates and a parabola is an approximation to an orbit. My current thought is that projectiles don't travel in a parabola because if the Earth ...
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### Ball trajectory in the game of pétanque - unexpected drag results

Context A classmate and I (about college level, not physics majors)need to evaluate the different physical factors at play during a game of pétanque. We thought about estimating the importance of air ...
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### Does high pressure make drag on a wing?

Say you have a plate facing the airflow right over a wing. Not attached, but just right over it. If flow separation and drag on the rear side of the plate (rear meaning the trailing edge of a wing) ...
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1 vote
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### Can frictional force be un-aligned with flow direction?

There is a well known solution to Navier-Stokes equations for atmospheric boundary layer according to Ekman (see for instance PalArya's book "Introduction to Micrometeorology" or Holton's &...
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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 ...
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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 (...
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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 ...
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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 ...
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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 ...
1 vote
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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, ...
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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 ...
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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 ...
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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?
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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. ...
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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 (...
1 vote
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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 ...
1 vote
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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 ...
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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 ...
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### 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 ...
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