# 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.

1,108 questions
Filter by
Sorted by
Tagged with
1 vote
33 views

### Signum function and friction

There've been some times where I've seen people including the signum function, $\text{sgn}(v_x)$ in equations of motion to account for the instant when the horitzontal velocity component, $v_x$, ...
53 views

### Why Is Wind Energy Velocity Cubed Instead of Squared?

Formula for everything seems to be squared, for example, kinetic energy $KE = \frac{1}{2}mv^2$ But for wind energy, this formula is cubed, e.g. $\frac{1}{2}\rho A v^3$ I couldn't find any results for ...
16 views

### Drag coefficient of an oscillating film in a turbulent flow regime (stirred tank), experiment or theoretical?

I have been recently assigned to a new project and brushing up my fluid mechanics from years ago, so sorry if the question is too stupid to post here. The goal is to quantitatively measure some form ...
28 views

### Complex shape drag coefficient

Is there theoretical way to compare drag coefficient of complex shapes without full CFD simulation ? For example which of these shape have or could have best drag coefficient or could any be improved ...
1 vote
52 views

### How do I rigorously prove that a ball dropped straight down doesn't move sideways (with quadratic air resistance)? [migrated]

Consider a 2D problem in which I drop a baseball straight down from some height. In this regime, one can show that the dominant contribution to the drag is a quadratic dependence directed opposite the ...
1 vote
54 views

### Air resistance in the Cavendish Experiment

Would air resistance be an issue in the Cavendish experiment or are the velocities so low as to be irrelevant? Could it cause the experiment to fail?
686 views

### In beer, why do bubbles travel faster upwards in the center?

This is a very odd question, but I just so happened to be observing a pint of beer and realized that the bubbles floating up seemed to travel faster towards the center of the glass than towards the ...
9 views

### Why doesn't the ratio of inertial to viscous forces ($R_e$) depend on the object shape - frontal vs side area?

Why doesn't $R_e$ depend on frontal and side area? - Understanding Reynolds number in the context of varying object geometries. I have not taken a fluid dynamics course, but have been reading up on ...
1 vote
59 views

### Graph of acceleration against time?

Considering no air resistance, the acceleration time graph for a free falling object would be a horizontal line as the acceleration remains unchanged. When we do take into account air resistance, the ...
19 views

### Frictional drag coefficient for flat plate normal to a uniform flow

In the case of a flat plate perpendicular to a uniform flow, it is commonly understood that for high Reynolds numbers, the drag coefficient ($C_D$) is known to be around 2.0. While many references in ...
22 views

### Why does a hemisphere facing into oncoming fluid fare slightly better than a wedge?

I saw this graphic on Wikipedia giving the drag coefficient of a variety of shapes placed into an oncoming fluid medium: https://en.wikipedia.org/wiki/Drag_coefficient#/media/File:...
106 views

### The solution of linear air drag and transcendental number $e$

I was watching a course about classical mechanics and in the chapter on air resistance the instructor wanted to show how transcendental numbers appear to the solution of linear air drag differential ...
68 views

### Numerical Method for solving Newtonian Equation of Motion for Particle experiencing drag in fluid flow

Currently, I have a fluid solver that can calculate the lift and drag forces acting on a body on a per timestep basis. This means that I have data regarding the hydrodynamic forces only for the ...
174 views

### Why does the angle for maximum range decrease in the presence of drag?

In the absence of drag, the angle to launch a projectile is 45°. In the presence of drag, the angle to attain max range is complicated. However, there seems to be consensus that it has to be less than ...
43 views

### How is the Reynolds number derived(my derivation is wrong)?

I'm a HS student so please dumb it down. I'm looking into the Reynolds number of a sphere sinking in a fluid, here's what I got. Inertial drag force = 0.5 * 0.47(CoefficientOfDragSphere) * rho(...
28 views

### Vertical Projectile with linear air drag

If a spherical ball of mass $m$ is thrown upwards with an initial velocity $v_0$ and it experiences linear drag, how do we come up with expressions for $v(t)$ using Newton's second law (taking up as ...
53 views

### Friction over a rotating ball under water

What's the friction force over a rotating ball under the water (or any other fluid)? The center of the ball is at rest, so I'm only interested in the slowing down of the rotation of the ball. My first ...
20 views

### Settling velocity of a particle in a Bingham fluid

I am trying to calculate the settling rates of a particle (xenolith) in magma in order to infer the magma ascent velocity. Assuming the fluid is Newtonian, this can simply be worked out using Stokes ...
29 views

### Are meteors heated primarily through radiation or convection (or both)?

From what I read meteors compress the air in front of them, increasing the air's temperature massively; this in turn is what heats the meteor. My question, which I can't seem to find a clear answer to ...
3k views

### Does the Earth experience air resistance?

Consider the earth body excluding the atmosphere, undergoing circular motion around the sun. Does it experience air resistance due to the atmosphere?
1 vote
38 views

### How does length effect drag?

Section of pipe: 20mm diameter, 2000mm length, hemisphere end cap. Moving horizontally through water, I think that the coefficient of drag would be approx. 0.42. How would the length of the pipe ...
21 views

### Optimum baseball distance from velocity

I am trying to come up with an equation that is able to approximate the magnitude of velocity of a baseball after it travelled a certain distance in the $x-$direction given the ball is thrown at an ...
27 views

### Unreasonable values obtained for a simplified helicopter in equilibrium

I'm attempting to analyse a simple model of a helicopter. For one of my equations, I'm summing the forces in the x direction (forward motion). There are only really two forces acting on the helicopter,...
3k views

### Would an adhesive surface have more air resistance?

Imagine spreading double-sticky tape all over the surface of a car or a plane. Would there more significantly more aerodynamic drag as a result of the adhesive 'sticking' to air molecules and slowing ...
1 vote
83 views

### Shooting a bullet in motion

If a bullet is shot from a firearm from a moving car in the direction of movement, would the speed gained with respect to the car be same as the speed of a bullet that is shot from an immobile gun? I’...
140 views

### What causes drag crisis?

While reading the Wikipedia article on Drag Crisis, I found: The drag crisis is associated with a transition from laminar to turbulent boundary layer flow adjacent to the object. While, the ...
68 views

### Lift and drag forces in parachuting

EDIT: guys, I am not a physicist and it is not my study field, So even if you see my question is silly to be answered, I hope you can give me a clue. I hope you are doing well. I have some questions, ...
87 views

### Is the sensation of falling purely due to air resistance?

When I jump off of something, even with eyes closed I can be pretty certain that I'm falling due to the associated sensation of falling. However, as gravity should be affecting each of my internal ...
1 vote
67 views

67 views

### Drag force on a bicyclist

Recently, I wrote an introductory physics exam where I encountered the following problem: We look at a bicyclist with the wind drag force $\vec{F_R}(t) = -k \vec{v}(t) |\vec{v}(t)|$ who accelerates ...
1 vote
58 views

### Husband and Wife with Metal and Fabric Parachutes [closed]

Let's suppose: an open parachute made of fabric with a lady hanging below, starting from stand still, falls from 5000 meters. Another parachute made of thick metal, with the same size and shape as the ...