What is Drag force: Definition and 164 Discussions

In fluid dynamics, drag (sometimes called air resistance, a type of friction, or fluid resistance, another type of friction or fluid friction) is a force acting opposite to the relative motion of any object moving with respect to a surrounding fluid. This can exist between two fluid layers (or surfaces) or a fluid and a solid surface. Unlike other resistive forces, such as dry friction, which are nearly independent of velocity, drag force depends on velocity.Drag force is proportional to the velocity for a laminar flow and the squared velocity for a turbulent flow. Even though the ultimate cause of a drag is viscous friction, the turbulent drag is independent of viscosity.Drag forces always decrease fluid velocity relative to the solid object in the fluid's path.

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  1. M

    Free Body Diagrams and Forces

    I don't even know how to begin this. I know that I need to somehow account for the drag force that duck 3 is causing on the first 2, but I don't know how to deal with that. I am asking for someone to help me get started, not to give me the answer.
  2. I

    Motion of a Parachuter (Terminal Velocity, Time of Flight, Distance)

    (a) -98 m/s (b) 490 m (c) My understanding is that at terminal velocity the net force in the y direction must be zero. Therefore: F_y = ma = 0 Only drag and weight forces act on the skydiver so: F_D + mg = 0 F_D = -mg -0.75*v = -82*(-9.8) v = -1071.5 m/s The value I get for v appears to...
  3. eddiezhang

    I Drag Coefficient of a 'flexible' object (e.g. a piece of paper)

    Hi all and thanks for your time. I'm a little new to this site and was unsure what the prefix to this post should be, so I put it under 'intermediate'. Imagine having a piece of paper glued to the palm of your hand. You swing your hand down and the edges of the paper bend backwards because of...
  4. Y

    I Force applied on sphere by turbulent flow

    Hello everybody, I am thinking of the following problem: A sphere a radius r is in a much larger container of radius R. In this container, a fluid continuously flows with turbulent conditions from bottom to top. I would like to approximate the force pushing the sphere up. Some calculations I...
  5. Tobi9242

    Mathematical model for drag on tether

    I have a model for airs density as a function of height I would imagine the speed can be describes as the angular velocity times length The coefficient of drag can be found online, seems to be around 1.17 for a cylinder It seems to me that im going to need an integral somewhere, but can't quite...
  6. H

    I Fluid dynamics: drag coefficient and pressure at the stagnation point.

    Hi, In my textbook the author say that the drag coefficient is the drag force divided by the pressure at the stagnation point time the area perpendicular to the stream. ##c_d = \frac{2F_d}{\rho v^2 A}## To get the pressure at the stagnation point I'm using Bernoulli for an incompressible fluid...
  7. Q

    How can I show the drag force-velocity relationship of a shuttlecock from my recorded trajectories?

    For a school project, I’m looking at modelling the vertical trajectory of a shuttlecock. I have several videos of trajectories, along with velocity and position data from LoggerPro. I’m aware that for a shuttlecock, the drag force is proportional to velocity squared, but is it possible for me to...
  8. K

    Engineering Designing a Cup Anemometer

    First, this class uses Frank White's Fluid Mechanics textbook. This particular problem is taken straight from chapter 7, which is on "Flow Past Immersed Bodies" and is basically focused on external flow, geometry effects, and boundary-layer conditions. So I imagine that the problem makes use of...
  9. Y

    B Terminal Velocity Equation in vertical cylinder with some fluid

    I just have a question that could you guys make an equation that expresses the terminal velocity based on followed condition? - When diameter increase, velocity decrease - velocity should change depending on both cylinder and sphere's diameter - We know every variable - The sphere is in...
  10. K

    Iron block dropped into a container of water sitting on a scale

    Does the scale change during the block sinks? I am so confused... Is there any difference on change of scale with the applying of drag force?
  11. T

    Relationship between Drag Force & Viscous Torque on USA Football

    Hello, I am a Physics undergrad degree graduate who is attempting to do a personal project involving the projectile motion of an American football in a 2D space. I want to take into account the drag force that the ball will experience and also take into account the spin of the football (in the...
  12. T

    Quadratic Drag Force: Solving Differently

    But the answers to these two questions confuses me. For the first question the answer goes like: $$m\ddot y = -mkv^2-mg$$ $$\therefore \ddot y = v\frac{dv}{dy}$$ $$\therefore v\frac{dv}{dy}= -kv^2-g$$ but for the answer to the second question we have: $$m\dot v = mg - cv^2.$$ Both questions...
  13. E

    Drag force on a descending sphere

    i tried a force balance around the sphere but the weight of the displaced fluid is greater than the weight of the sphere which gives a net acceleration upwards and no terminal velocity but the book says that the terminal velocity has a certain value from there the exercise is meaningless to me...
  14. B

    Direction of acceleration of a projectile with drag force

    First and foremost, thank you so much for your help! I'm new to Physics Forums, and this is my first post. I thought I understood the problem, but as I moved on to the subsequent parts of it became apparent that I was missing something. I set up my ##F = ma## equation as below, and solved that...
  15. tanaygupta2000

    Motion involving drag force

    Since given F = -kdx/dt so I equated mx'' = -kx' which gave x(t) = A + B exp(-kt/m) hence v(t) = (-kB/m) exp(-kt/m) and using v(0) = u, v(t) = u exp(-kt/m) then I...
  16. jisbon

    Upthrust, drag force in water

    So using FBD, I came out with: since it reaches terminal velocity, I can assume F=0, thus mg = upthrust +drag So my density = mg - drag force/g * volume However the answer seems to be wrong from the answer key I was given. Any ideas why? Thanks
  17. T

    Calculating the drag force on a spherical object with holes

    I am looking for a bit of guidance on how one could calculate the drag force of a sphere with holes in the sphere falling through a fluid, in my case water. So I know for a low Reynolds number the drag force on a sphere is given by stoke law, but what I would like to do is calculate the drag...
  18. A

    Why does Cd increase until Mach1 while drag force increases?

    When I was looking a project that included Mach vs Cd and Mach vs drag Force for a grid fin at different altitudes with different mach numbers, I saw that as Cd approached Mach 1, it increased but after passing Mach 1, it started to decrease but the drag force kept on increasing. I initially...
  19. M

    Drag Force Acting on an Object with Respect to Velocity

    Homework Statement The final velocity of an object falling through air from various heights is given. From this, can you derive an equation for the drag force acting on the object with respect to velocity? Homework Equations Maybe relevant? Wno drag$$=mgh,$$ Wreal$$=\frac{1}{2}mv^2,$$...
  20. H

    Varying Gravity and Air Resistance in projectile motion

    Salutations, I have been trying to approach a case about projectile motion considering variation of gravity acceleration and air resistance: A spherical baseball with mass "m" is hit with inclination angle $\theta$ and launching velocity $v_0$, then, the wind has a drag force equals to ##F=kv##...
  21. EelAnes

    How to calculate the drag force?

    Problem How to calculate the drag force of the model helicopter using the given data above? Research Question How does increasing the length of the wing planform of a model paper helicopter affect the time it takes the helicopter to fall to the ground and hence the air resistance? Variables...
  22. K

    Lift and Drag force in a Wind Tunnel

    Hello guys, I am trying to calculate the lift force and drag force in a wind tunnel at my school as a part of a project that i am doing. I am varying the length of the airfoils and trying to measure the lift force and drag force. I have 3-d printed 7 airfoils. However, I am not able to find any...
  23. babaliaris

    Air drag force: Why heavy objects accelerate faster?

    I've done the math but because i can't find this answer anywhere in the book which I'm reading and on the web, I would like to be sure if my calculations are correct. I know that if two objects (starting at the same time) are free falling without a drag force being applied to them, the...
  24. David Koufos

    Air resistance differential equation

    Hello all, I want to say thank you in advance for any and all advice on my question. My classical mechanics textbook (Marion Thornton) has been taking me through motion for a particle with retarding forces. The example it keeps giving is: m dv/dt = -kmv which can be solved for: v = v0e-kt...
  25. Ushitha Dissanayake

    How do I find the terminal speed of a body in water?

    Homework Statement A baseball has a terminal speed of 42 m/s in air (ρ = 1.2 kg/m^3). What would be its terminal speed in water (ρ = 1.0 x 10^3 kg/m^3)? A) 0.05 m/s B) 1.5 m/s C) 18 m/s D) 42 m/s E) 1200 m/s Homework Equations D=½Cρ*Av^2 where the magnitude of the drag force (D), relative...
  26. N

    Velocity of a football with and without drag

    Homework Statement A professional thrower projects a football straight up in the air. 1. Assuming there is no air drag on the football, find the speed of the football as a function of height as the ball goes up. 2. Assuming the air drag on the football varies linearly with speed, find the speed...
  27. R

    How increased mass and drag affect speed

    Hello. I read an article about aerodynamics. http://www.cyclist.co.uk/in-depth/2873/fat-v-skinny-who-goes-downhill-faster I'm a little bit confused with this statement regarding mass, drag, and velocity: "When you increase the mass the speed increases by cubic function, whereas if you...
  28. grandpa2390

    What is this formula being used to calculate drag force?

    Homework Statement I'm writing a program to plot the trajectory of a baseball. the formula is given to me by the book, but I'm not sure what it means. Homework Equations The Attempt at a Solution I am given that v_d = 35 m/s and delta = 5 m/s what is v? as in what does it represent? is it...
  29. V

    Find the point when velocity is momentarily zero

    Homework Statement [/B] A block travels in the positive x-direction with some velocity ##v_0##. It is subject to a drag force $$F(v)=-F_0e^{Kv},$$ where ##F_0,\,K## are positive constants. Find the point in time when the velocity of the block momentarily goes to zero. Find how far the block has...
  30. S

    What does FL represent in the drag coefficient equation?

    So I did a project about a year ago and I can't remember one of the things I wrote in this equation. The equation apparently I got it from NASA's website. https://www.grc.nasa.gov/www/k-12/airplane/dragco.html This is my equation CD = FL/ (0.5 * Air viscosity * V^2 * Area) = 0.4These are the...
  31. R

    Lift and Drag Force in ANSYS CFX

    How i can know the magnitude of lift and drag force from ansys cfx?
  32. V

    2D equation for projectile with linear drag force

    Homework Statement Given the equations a) find the solution to the problem (1) in vectorial form, by first writing equation (1) in component form and then solving the two parts separately. These can then be combined to obtain the vector form of the solution. b) solve the results of the...
  33. S

    Automotive Motor Selection for Roller: Diameter 300mm, Length 1350mm, Inertia 3.95 KG.M

    i need to select the motor for a roller of Diameter 300mm , length 1350mm having inertia 3.95 KG.M ,Which needs to accelerate from 0 to 600MPM at 20 sec . Assuming existing web tension acting on the roller 20 N/M. THANK YOU
  34. S

    Drag force on a flat plat like a pendulum?

    Hi , please i want to know if i have flat plate (rectangle) but its fixed like pendulum (fixed from one end and free at the other end and can rotate around this fixed end) i want to know the drag force due to air on this plate?
  35. A

    Drag Force: Mass & Why It Doesn't Affect Object

    Why drag force doesn't Depend on the mass of the Object?
  36. M

    Find the time dependence.... (Mechanics)

    Homework Statement I am not looking for a solution to the problem, as much as I need a clarification on what it's asking for. The problem: "A particle of mass m slides down an inclined plane under the influence of gravity. The particle is starting its motion from rest. Find the time dependence...
  37. Kiwigami

    Understanding Drag Force against a non-linear Force

    Homework Statement I'd like to understand Drag Force better; but school always ignores it. Thus, I'm asking this purely out of obssession. I'm picturing a scenario where a non-constant force is pushing an object horizontally, ignoring friction. But, I'd like to understand how Drag Force...
  38. R

    Finding the average magnitude of the drag force

    Homework Statement A saucer of mass 1.75x10^9 enters 1.the gravitational field of PlanetX and enters its atmosphere; the gravitational field of the planet is 10.6 m/s2 and is considered uniform throughout the 80-km thick atmosphere. If the saucer enters the atmosphere at 460 m/s and slows...
  39. U

    Drag force on a cylinder in an air tunnel

    Homework Statement Let's have a cylinder in air tunnel. The air is flowing around cylinder. I want to calculate a net force acting on the cylinder. Part of the incoming air hits the cylinder and its trajectory direction changes. For that reason we can see straight behind the cylinder lower...
  40. gelfand

    Drag force with differential equations, finding max speed

    Homework Statement A submarine engine provides maximum constant force ##F## to propel it through the water. Assume that the magnitude of the resistive drag force of the water experienced by the submarine is ##kv##, where ##k## is the drag coefficient and ##v## is the instantaneous speed of...
  41. R

    How the angle of launch affect the range?

    Homework Statement I'm about to conduct an experiment about factors that affect the flight of an elastic band. The aim of this experiment is to find how the angle of launch, when shooting a rubber band, affects the range or distance of the shot. Do you suggest to consider the drag force? like...
  42. R

    If air drag is a factor, how will it affect a projectile?

    If air drag is a factor, how will it affect a projectile’s trajectory qualitatively? Its velocity? Its acceleration?
  43. Macykc2

    Solving Boat Speed & Distance with Drag Force

    Homework Statement A boat with initial speed vo is launched on a lake. The Boat is slowed by the water by a force F=-αeβv. Find an expression for the speed v(t), and find the time and distance for the boat to stop. Homework Equations Drag force F=-αeβv alpha and beta are not specified as to...
  44. Arman777

    Drag Force Ratio: Jet vs Transport at 1200 km/h, 15 km Altitude

    Homework Statement Calculate the ratio of the drag force on a jet flying at ##1200 km/h## at an atttude of ##15 km## to the drag force on a prop-driven transport flying at half that speed and altitude.The density of air is ##0.38(\frac {kg} {m^3})## at ##10 km## and ##0.67(\frac {kg}...
  45. victorhugo

    What do we know about the formula for air drag force?

    Is it the typical "get some results and stack the maths together and chuck in some constants to make it fit to get some approximation" or do we understand the rules behind it to derive the formula, such as how the molecules repel each other and how energy is transferred depending on temperature...
  46. Nivek Writer

    How to calculate the drag force of a Bussard ramjet?

    Hello everyone, I am making a paper on the possible applications for nuclear fusion. One of these possible applications is a Bussard ramjet. I'm trying to calculate if Bussard ramjets are feasible, based on their thrust and the drag they experience. A Bussard ramjet would use a very big...
  47. nysnacc

    Drag force deceleration

    Homework Statement I forgot if the deceleration is -0.003v or same here -0.003v2 Homework Equations v = u + at (first acceleration) dv/dt = a (deceleratioin) = -0.003v^2 The Attempt at a Solution From first equation, 342.2 = 0 + 30*t1 t1= 11.407s From 2nd equation, dv/v2 = -0.003...
  48. Elvis 123456789

    How can I be sure of my numerical result?

    Homework Statement In this problem you will do numerical computer calculations. A skydiver of mass 75.0 kg jumps out of a plane at an altitude of 30.0 km above the surface of the Earth. His parachute fails to open. Assume there is no horizontal motion and the initial velocity is zero. We...
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