Drag force Definition and 166 Threads

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. nysnacc

    Deceleration Calculation for Drag Force with Varying Units

    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...
  2. 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...
  3. Elvis 123456789

    Falling object in a gravitational field with v^2 drag force

    Homework Statement Consider a particle in a gravitational field that is also subject to a resisting force proportional to the velocity squared ( Fdrag = + or - cv2). a) Find the terminal velocity, vT, for the object as it falls. b) Show that for an object dropped from rest that the velocity...
  4. nysnacc

    Velocity Drag force and distance traveled

    Homework Statement Homework Equations Sum of force a = dv/dt v = integrate a + C The Attempt at a Solution I found the equation in terms of final v, initial v... however, on the right hand side, there is another v, and I think it is time dependent, so I am not sure which value should I...
  5. nysnacc

    Calculating Drag Force for Parachute: F=ma and Sum of Forces

    Homework Statement Homework Equations F=ma Sum of force The Attempt at a Solution Not sure if my a is correct, but actually, I need to have it in imperial (US) unit,[/B]
  6. Wanna_be_Feynman

    Distance a bullet will travel while shot underwater

    Homework Statement hey I am trying to work out the problem: If I shoot an ak47 underwater with 7.62x39mm ammunition, how far will the bullet travel before coming to a stop? Homework Equations The equation that I have used to find the drag force is the drag equation: F =1/2 p*A*C_d*v^2...
  7. R

    Can drag force and lift force be in the same direction here:

    In the attached picture, can I say that there is a lift force in the Y-direction, and a drag force too in the same Y-direction? FL proportional to V_fx2 ? FD proportional to V_py2 ? Is this equation of motion for the Y-direction correct here: ma = − mg − FD + V(rho)g + FL The lift force is...
  8. John Lam

    Calculate Vertical Displacement with Drag Force Equation | Physics Homework

    Homework Statement Assuming that the drag force magnitude is given by the equation D= bv, where b is the drag parameter and v is the instantaneous velocity magnitude of the object. (a) Show that the vertical displacement through which a dropped object must fall from to reach X% of its...
  9. Nurah

    Calculate Drag Force & Power for Long Cylindrical Antenna

    Homework Statement A long cylindrical antenna of 9 mm (0.009 m) diameter is mounted vertically on a car moving at 100 km/h (27.778 m/s). Antenna is 920 mm long (0.92 m). Calculate the power required to move antena through the air with standard kinematic viscositiy ν = 1.46 ⋅ 10-5 m2/s. The...
  10. A

    Differential equation for grav, boyant and drag force

    Homework Statement So there is a falling object, you have to take into account the boyant force, the pull of gravity and the drag force A time dependent distance equation is what we're looking for Homework Equations Fd=CdApav2/2 Where Fd is the drag force Cd is the drag coefficient A is the...
  11. J

    Finding maximum speed (known: Force output, drag, time)

    1. In general, dense fluids (such as water) produce a drag force that is directly proportional to the speed of an object moving through them. Suppose a boat is moving through the water and experiencing a fluid drag force of F=-8 v. Suppose the boat has a motor which can output up to 450 Newtons...
  12. B

    Drag, terminal velocity, and force.

    Homework Statement Coal miners often find mice in deep mines but rarely find rats; let’s see if we can figure out why. A mouse is roughly 5 cm long by 2 cm wide and has a mass of 30 g; a rat is roughly 20 cm long by 5 cm wide and has a mass of 500 g. Assume that both have a drag coefficient CD...
  13. T

    Is Drag Coefficient Constant for same shape, different size?

    I've read that drag coefficient depends on the shape of the object but I am confused as to what shape means. Does it mean geometric shape or is area included in that? Say I have one sphere of radius r and keep fluid velocity, density, and viscosity constant and find its drag coefficient. Would...
  14. D

    Drag force of a cylinder with it's axis parallel to the flow

    Hello, I would like to know how to calculate the drag force per unit length of an infinite cylinder with it's axis parallel to the flow field, I had read about a post here previously titled " Drag force on cylinder in parallel flow" but the slender body approximation is not valid for inifinite...
  15. J

    Difference between viscuous force and drag force?

    What is the difference between viscuous force and drag force? Are they the same?
  16. T

    How Is Terminal Velocity Calculated in a Submerged Block System?

    Homework Statement Consider two blocks connected by a light, inextensible string over a light pulley as follows: The slope is frictionless and the masses are released from rest. The mass m1 is 3 kg and the mass m2 is 4 kg where m2 is submerged completely (from the beginning) in a liquid of...
  17. toforfiltum

    Variation of Force-time graph for person opening parachute

    Homework Statement Homework Equations F∝v The Attempt at a Solution I chose C because I thought that at time T after opening the parachute, the resisting force on the diver will increase. But it is not so since the answer is B. Is it because the diver has reached terminal velocity? Even so...
  18. C

    Energy consumed by variable drag force when stopping?

    I was trying to roughly calculate the energy that could be recovered by regenerative breaking when bringing a vehicle to a stop, so I calculated to total kinetic energy and then tried to calculate the work done by air resistance that would take away from the energy that could be captured. So I...
  19. Dain Ironfoot

    How to calculate distance required for observable difference

    Me and my grandfather got into a "debate" (more like one-sided argument) on whether objects fall at the same rate on Earth independent of air resistance or not. He claims that "If you drop 2 objects from an airplane -- like a car and a marble, both objects would hit the ground at the same...
  20. K

    When will the fishing boat and the speedboat meet?

    Homework Statement a) A fishing boat of mass m moves through water in the +x direction. At time t = 0, it is at location x = 0 and has speed v0 at that precise moment, the boat’s captain turns off the engines and let's the boat drift. Taking the drag force into account, Fd=-Kv^2, calculate the...
  21. P

    Newton 2nd. 2D velocity fn. Distance (boundry conditions)

    I understand that this has been answered, but I can't follow it. My apologies, physics is a realm I want to understand but it doesn't come naturally and I have no High school physics background just 1st yr Engineering physics. (passed with supps.) A particle is projected vertically upward in a...
  22. F

    Why Does Drag Force Depend on Cone Shape and Size but Not on Mass or Gravity?

    Problem 2.14: Explaining the Simplification from Street-Fighting Mathematics by Mahajan "Why is the drag force independent of the gravitational acceleration g and of the cone's mass m (yet the force depends on the cone's shape and size)?"Context Imagine two paper cones formed by taping together...
  23. P

    Find k & a for Infinite Distance Travel w/ Drag Force F=kv^a

    Homework Statement Only force acting on body is drag force $$F=kv^a$$ where k is constant, a coefficient bigger than zero and v is velocity. Body is given initial velocity u. Find a such that body travels infinitely large distance.[/B]Homework Equations $$F=kv^a$$ $$F=m(acceleration)$$...
  24. M

    How do you do projectile calculations, but with drag force?

    And how do you find the drag force?
  25. T

    Drag force on a sphere moving through a fluid

    A body moves through a fluid, a retarding force due to turbulence may be experienced. In case of a sphere of radius R moving with speed v through a stationary fluid of density p which it at rest, this force is given by F = kp (R^2) (v^2) k is a constant. Why F is proportional to kp (R^2) (v^2) ?
  26. M

    Testing Drag Force on a Sphere

    Hi all. This is my first question on these forums. I am given a task to test out whether or not FD=1/2 CDAρv2 is a good model to test drag force. Where CD is described by Reynold's Number. We have a balloon a small ball and a myriad of basic physics lab equipment.What is a experiment I could...
  27. D

    Conservation of Energy, Car Driving with Drag Force

    Homework Statement A 710kg car drives at a constant speed of 23m/s . It is subject to a drag force of 500 N. What power is required from the car's engine to drive the car (a) on level ground? (b) up a hill with a slope of 2.0o? Express your answer to two significant figures. Homework Equations...
  28. C

    Drag Force from Cable: Calculate & Understand

    Hi, I have a raft that move along in a tunnel with the water flow (no propelling engine). A neutrally bouyant cable is attached to the device at the back to supply power for the apparatus on the raft. The cable is about 14mm in diameter and the max length of cable can be 5km. May I ask how can...
  29. steves1080

    Calculate drag force on a temperature probe inserted in a water pipe

    I'd like to add a temperature probe to a 4" water pipe downstream of a centrifugal fill pump, but I am afraid of the probe shearing from being subjected to a constant force from the upstream pump (which pumps at about 400 gal/min). Naturally, my thought was to use the drag force equation, but I...
  30. K

    Experimental Derivation of the Drag Force

    I am trying to experimentally derive the drag equation. I have dropped coffee filters with varying masses and determined their resulting terminal velocity. I plotted the data and found that the mass of the coffee filter is proportional to the terminal velocity squared. I was now wondering how I...
  31. patrickmoloney

    Drag Force - Air Resistance Question

    Homework Statement A skydiver drops o¤ an outcrop at the top of a sheer face on a mountain and falls vertically downwards. Let v(x) be the velocity of the skydiver at a vertical distance x below the drop-off point. As the skydiver falls he will experience a drag force of magnitude...
  32. P

    Velocity of a Spherical Particle in a Viscous Liquid: Integrating Drag Force

    Homework Statement An object moving in a liquid experiences a linear drag force: D⃗ =(bv, direction opposite the motion), where b is a constant called the drag coefficient. For a sphere of radius R, the drag constant can be computed as b=6πηR, where η is the viscosity of the liquid. Find an...
  33. T

    Calculate Drag Force for a 14.7mm Sphere in Oil with Given Parameters

    A sphere, 14.7 mm in diameter, drops at a rate of 0.08 m/s in oil µ = 0.1 Ns/m^2 , σ = 0.85 ). Calculate the drag force acting on the sphere. [Answer: 1.85e-3 N] F_d=0.5*rho*C_d*A*u^2, Re=u*p*L/μ I attempted to find the Re, but am struggling on finding the coefficient of drag...
  34. X

    Drag Force Equation: Sphere vs 1/2pv^2C_dA

    Homework Statement Hi, i have a peculiar question after watching MIT lecture:http://ocw.mit.edu/courses/physics/8-01-physics-i-classical-mechanics-fall-1999/video-lectures/lecture-12/ What is the difference between the equation representing the drag force for a sphere...
  35. S

    A question about linear drag force

    My classical mechanics textbook says that, for a projectile, the linear drag force is given by f = -bv and the second law is written as m\ddot{r} = mg - bv (a second order differential equation) which can be rewritten as m\dot{v} = mg - bv (a first order differential equation) because the forces...
  36. A

    Air Resistance (Drag Force) and Terminal Velocity

    Homework Statement "How does air resistance affect terminal velocity" Homework Equations N/A The Attempt at a Solution I know most of the answer of this, however I am just wondering say take a parachutist for example, if the air resistance is the resultant force, then in order...
  37. D

    (simplified?) Air drag force question.

    My issue/knowledge Hello all, I think this is my first time posting a question here (I have read the guidelines). This problem is not in my textbook or notes, and I'm not sure how to go about it. Online all I can find about air drag equations requires knowing variables which I'm not given here...
  38. A

    Drag Force on a Streamlined Body

    Hi, I know that the drag force on an object: Fd= 1/2 . ρ . v^2 . Cd . A where A is the reference area. But in the case of a streamlined body, I don't know what will be taken as the reference area. Should it be the largest cross-sectional area of the body?
  39. I

    How do I determine the appropriate drag force equation for my problem?

    i have an object thrown up in the air with drag present. i want to know how much time it takes to reach the peak ie when v=0 m\ddot{x}=-mg-kv2 basically, i don't know which one to use for drag, I've seen bv being used before in problems, and I've also seen kv2 being used before in...
  40. A

    Linear Drag Force Homework: Acceleration & Constant Speed Calculations

    Homework Statement We sink ball with density 1450 kg/m^3 in some liquid with density 1400 kg/m^3 a) What's acceleration in moment we drop the ball? b) With what constant speed will the ball sink in balace? Assuming that the drag force is linear. Radius of ball is 3mm and viscosity of...
  41. W

    Gas consumption to overcome drag force

    Homework Statement A car moving with speed v is subject to a drag force F_{d}=0.5\rho A c_{d}v^{2}, where \rho is the density of air (1.25 kg/m^{3} at STP), A is the cross sectional area of the car, and c_{d} is the drag coefficient. A Honda Civic has A=1.9 m^{2} and c_{d}=0.36. Assuming...
  42. Y

    Question on coriolis effect with drag force

    I really need help with this question. A small floating object initially moves with velocity v on the surface of a liquid at latitude λ. The drag force due to liquid is F=-αv. Find the shape of the trajectory of the object due to drag and Coriolis forces. What will be the trajectory if α=0 ?
  43. K

    What is the average drag force on a softball pitched at 99.6 km/hr?

    A softball having a mass of 0.250 kg is pitched at 99.6 km/hr. By the time it reaches the plate, it may have slowed by 10.8 percent. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is 15.2 m. F=ma...
  44. R

    How do I calculate the drag force on a motorboat accelerating from a dock?

    1. A 940 kg motorboat accelerates away from a dock at 2.2 m/s2. Its propeller provides a thrust force of 3.9 kN. What is the drag force exerted by the water on the boat? 2. I know that the force can be get by F= m a 3. My teacher told us to draw a free body diagram to get all the forces acting...
  45. U

    Pebble falling into water; drag force

    Homework Statement The drag force experienced by the spherical pebble in water is given by: (0.5)CpwAv2 mass of pebble = 83.8g radius of pebble = 2 cm C = 0.7 (a) Write down the differential equation governing pebble's descent. (done) (b) Derive an expression for terminal...
  46. B

    Drag force and maximum velocity

    Homework Statement So for my intro engineering class one homework problem is given as follows. "Considering only aerodynamic drag force, calculate the maximum speed (in mph), that a vehicle would experience with the following specifications." Horsepower = 330 Mass density of fluid = .077...
  47. Blandongstein

    Hydroynamics: Stoke's Law, Find work done by drag force

    Homework Statement A water droplet starts falling from rest from a height h and a quires the terminal speed just before reaching the ground. If g(acceleration due to gravity) is assumed to be constant and the radius of the drop is r, find the work done by air drag. The density of air is...
  48. Vigardo

    Modelling drag force of big spheres in air.

    Hi all, I´m a researcher in computational biology thinking on topics quite far from my field. Would you help me? Thanks in advance! I want to calculate the drag force in air of big rigid spherical and cylindrical objects at speeds form 0 to 100 Km/h. Their diameter would range from 1 to 20m...
  49. S

    Calculate Drag Force for Tennis Ball at 251 km/h

    Homework Statement A tennis player hit a serve of 251 km.h-1 in a match. Calculate the Drag Force acting on the tennis ball. Diameter of ball is 6.5cm, density of air is 1.3 kg.m-3 and air viscosity is 1.8x10-5 kg.m-1.s-1. Homework Equations Drag Force is: Fd= \pi.d2.CD.pf.u2.1/4...
  50. M

    Please help me to calculate drag force and lift force

    Homework Statement Hello guys, I am here and really need your help. In the figure below, the water flow from inlet and then out at outlet with velocity, v = 0.71 m/s. The objective is to calculate find the drag force and lift force act on fishing lure. I have done Ansys Fluent analysis but...
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