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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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No friction in pure rolling - how about driving a car?

I remember the un-intuitive result that pure rolling without acceleration involves no friction by the law of conservation of angular momentum. Conjectures: I understand that when I'm driving a car at ...
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29 views

Thrust needed from an engine to reach orbit

Assume you had an airplane with magical engines that didn't need fuel, air or power, to operate. What thrust to weight ratio would the airplane need to reach orbit? Assume not needing fuel, air or ...
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Why are golf balls the only (famous) object with dimples?

To my knowledge there isn't anything that uses dimples to reduce drag. It's weird to hear why dimples are useful and help the ball go farther while at the same time finding no other examples. I ...
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Manipulation with drag force [closed]

I have a problem to solve concerning drag force and its relation with velocity. The problem is following: A car of mass m is propelled forward starting from rest by a constant force +F. Use b for the ...
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2answers
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Did Usain Bolt really sustain 11 horsepower of exerted power during the 100 m sprint?

I've just come across a WP article which says: "The Jamaican sprinter Usain Bolt produced a maximum of 3.5 hp (2.6 kW) 0.89 seconds into his 9.58 second 100-metre (109.4 yd) dash" Out of curiosity, I ...
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38 views

Which way would objects, inside a container falling through earth's atmosphere, move, relative to the container?

Say, a sealed hollow container with 1 atm air pressure inside, is falling through earth's atmosphere. It is falling steadily with one side always facing the ground (Front Side) Inside the container, ...
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Aerodynamic Force Decomposition

We know that aerodynamic drag is proportional to the square of the velocity of the incoming flow: $$D=kV^2.$$ If I decompose velocity into arbitrary orthogonal $x$-$y$ directions:$$V_x=V\cos\theta\\...
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With drag, why does it take longer for an object thrown upwards to fall back down than it does for it to reach its highest point? [duplicate]

Why does it take longer for an object thrown upwards to fall back down than it does for it to reach its highest point? We can draw a free body diagram for when the object is falling down and for when ...
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39 views

How to calculate air resistance? [closed]

What is the best way to calculate or take into account air resistance? I have an assignment which goes as: Drop an object by itself and with a parachute, calculate air resistance for the parachute. ...
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24 views

Does the Choice of Coordinate System Matter for a Particle Falling Downwards in a Linear Medium

I have a question regarding John Taylor's treatment of a particle falling down in a medium that exerts a linear drag force (Chapter 2 of his book "Classical Mechanics").First some background, he ...
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4answers
68 views

What is the reason terminal velocity changes with radius?

I know that terminal velocity equals to some multiple of radius square. What is the physics behind this relationship. Is it just because as terminal velocity increases, the surface area increases and ...
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fluid flow over a incline and decline slope

I was recently watching fluid flow simulations on a cone. And noticed that if the tip on the cone is facing in the opposite direction to the fluid flow i.e fluid flow in $+x$ and tip of cone in $-x$ ...
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Can pressure drag ever have a linear relationship?

I know from aerodynamics that pressure drag has a quadratic relationship for high Reynolds number of $10^4$ but what if the Reynolds number is between 1 and 10^3 say can pressure drag have a linear ...
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Why do 2 objects, when dropped, reach the ground at the same time? [duplicate]

2 objects of the the same volume and dimensions but with different weights are dropped from a sufficient height in which said objects can reach terminal velocity. Galileo's finding was that both ...
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28 views

How to calculate drag caused by string?

An example - I throw a tennis ball with a short string hanging off one side. As the ball flies the string is dragged to the side opposite the direction of the ball's velocity vector, anchoring the ...
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1answer
21 views

Small amplitudes and Stokes drag law

Why is it that on a damped harmonic oscillator or a pendulum in a fluid, the Stokes drag law in the fluid only applied to small amplitude oscillation compared to large amplitudes oscillations? Dose ...
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The effect of mass on the optimum angle of a projectile, taking into account air resistance

I know that air resistance causes projectiles to have an optimum angle that is below 45 degrees, however, when we compare projectiles of different masses, for example a golf ball and a ping pong ball, ...
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Does dark matter experience drag?

Is dark matter dragged around the galaxy by gravity as stars and groups of stars orbit the galaxy, and, if so, is its shape/distribution deformed? Similarly, would the Oort cloud be deformed by being ...
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gravitation (kinetic energy and angular momentum)

When a satellite in a circular orbit around the earth enters the atmospheric region it encounters small air resistance to its motion. then (1) kinetic energy increases (2) angular momentum decreases ...
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1answer
30 views

Why are there no coefficients of drag for cubes and cones of low Reynolds numbers

I am currently reading ''Fluid Mechanics-Fundamentals and Applications'' by Yunus A.Cengel and John M.Cimbala. I am currently reading about drag coefficients in chapter 11 and how it talks about the ...
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1answer
45 views

Resistance in fluids

Is atmosphere depth important in reaching terminal velocity in terms of slowing down an object. For instance, if a meteor was dropped from height $h_1$, would it hit the ground with the same velocity ...
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1answer
29 views

How does one calculate the energy used depending on the velocity and air resistance of an object [closed]

I'm in need of a equation that can tell me how much energy/work I need to move an object inside a low air-pressure tube. The equation should (if possible) include drag, object velocity and mass. If ...
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Is there a “solid dynamics” and are there optimal shapes for it?

I am interested in designing an object that can move swiftly through a more solid medium like rock or dirt. Is there any particular kind of mechanical shape (besides a conventional drill) like a ...
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How to calculate the drag force of a cyclist and the drag coefficient?

I have a creative math assignment which my class was tasked to do. Thus I decided to create my work on physics, more specifically aerodynamics. I want to create a function which calculates Drag with ...
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1answer
62 views

Why a rope grabbed by a single end seems to follow the hand that grabs it?

Context I am thinking about the physics of the movement of a rope in the context of a person running and grabbing a rope in one hand (the other end is "free", there is nothing attached). When the ...
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1answer
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Determining $v(t)$, time taken and distance covered by a plane given $a(v)$. Plus, reason why it is unreasonable.

GIVEN PROBLEM: A jet plane landing on an aircraft carrier deploys a parachute to slow itself. The acceleration achieved is $a=-0.005v^2 m/s^2$. a) If the initial speed of the plane is $60 m/s$ ...
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1answer
29 views

How to obtain the $dC_d/dC_l^2$ value from the drag polar of an airfoil?

I'm currently trying to do an initial design for a propeller. In order to do this I'm trying to use Xrotor. Xrotor allows the user to enter certain information about both the propeller geometry, ...
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1answer
39 views

Finding the drag force from the final velocity of a falling object

I know the velocities (v) of an object after it fell for respective distances (s). From that alone, is it possible to calculate the drag force at a specific moment in time? If not what else would I ...
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Where does this equation come from?

I am investigating about viscosity of fluids and I found the following equation to calculate the viscosity: $$\nu = \frac{2(\rho_s-\rho_l)\cdot g \cdot r^{2}}{9\cdot\Delta v} $$ The experiment ...
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1answer
40 views

Does mass slow down an object falling through the atmosphere? [duplicate]

If I throw two objects with the exact same shape and size, but one of them is heavier, will they arrive at the same time? We learn in basic Newtonian physics that mass doesn't influence the speed in ...
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46 views

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 ...
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1answer
62 views

Rocket equation and drag formula

i originally posted this question over at the math section but a guy told me to switch it to here instead. i'm writing an assignment on firework rockets and their trajectory. Now of course im doing ...
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1answer
64 views

Derive formula for air resistance $F = \frac{1}{2}CAdv^2$ through dimensional analysis

I have an assignment, where I’m required to derive the formula for air resistance for a falling object. $$ F = \frac{1}{2}CAdv^2 $$ where $C$ is drag coefficient, $A$ is the cross-sectional area, $...
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Equations for an object moving linearly but with air resistance?

If F be the independent force acting on the object and D be the velocity dependent force acting in the opposite direction of F. The net force accelerating the object is; $$F − D = ma$$ where $D = \...
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2answers
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Aerodynamics of cycling into a tail wind

I was looking at Steve Gribble's Cycling Calculator , and I noticed that the aero resistance was higher going 40 mph with a 20 mph tail wind than going 20 mph with no tail wind. Why is this? I always ...
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1answer
39 views

Effect of velocity upon kinetic friction

This question has been asked before... (Does the force of kinetic friction increase with the relative speed of the objects involved? If not, why not?), ...but there's a very specific part I'm ...
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66 views

Speed of a falling object

When an object is dropped, does it accelerate to terminal velocity? or is it at terminal velocity immediately?
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1answer
39 views

What forces the maximum speed of a cyclist on a steep climb?

I know that on a flat road drag is the main force, I have to provide as much force as the drag (and the friction in the drive train) produces. I can also see that the faster I ride, the harder it gets ...
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3answers
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Are there any cases where Stokes law does not apply in viscous fluids?

A friend of mine and I are conducting an experiment to find the relationship between terminal velocity and radius of a sphere (i.e trying to confirm Stokes law). We are using spheres ranging from 1....
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1answer
36 views

Find the drag coefficient from a ln(acceleration) v time graph [closed]

I don't have a huge amount of information to go on, but I basically have the decay of a pendulum v time, and then taking the decay of this graph, I have a plot of ln(Theta max) v time. From this I ...
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2answers
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Does free fall ever occur on the surface of Earth?

According to the definition of "Free fall", which is "Downward movement under the force of gravity only.", free fall only occurs when gravity is the only force acting on an object. But here on Earth, ...
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Rotational Motion, Kinematics, Air Resistance

When a body is thrown of height in a practical situation ( air is present ) considering air resistance is applying constant opposite force, we could calculate its speed by calculating acceleration ...
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1answer
2k views

Is there a way to calculate the time taken by a falling object to reach terminal velocity? [duplicate]

I know it is possible to calculate terminal velocity using air density, mass, and drag coefficient, but is there any way to calculate the time taken until that speed is reached (assuming air density ...
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1answer
97 views

Does the drag equation only apply to turbulent flow

I am doing an analysis of the motion of an object in air and so I'm first finding whether the flow is laminar or turbulent. From my research, I'm still a bit confused as to whether the drag equation ...
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1answer
51 views

If I push an object underwater, how long before it stops?

If I were to push an object that is completely submerged in water with a know force, how would I go about finding the distance it travels before coming to a stop given that I know the drag coefficient ...
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1answer
50 views

Is the mechanical power output of a car constant?

According to my textbook. The mechanical power output of a car is constant. My reasoning tells me otherwise though. According to a lot of pages on this forum related to the driving force of a car. ...
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1answer
118 views

I need to find the drag coefficient of a pendulum bob [closed]

Is it possible to find the drag coefficient of a pendulum bob from the damping caused on it during swinging. I will be able to measure its displacement from the point of origin and plot it against ...
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On the performance of Bolt in the 100 metre sprint - solving equation of motion [closed]

I'm looking at the following article(1) in which a mathematical model is used to describe the performance of Bolt (in general of a sprinter) in a 100 m sprint. The equation of motion is $$ m\dot u = ...
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4answers
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Why is $mg = bv$ and not $mg = -bv$?

I was given two formulas, $$F_D = -bv $$ $$F_D = -bv^2 $$ and was told that at terminal velocity, $$v = \frac{mg}{b} $$ which implies that $$mg = bv$$ $$mg + (-bv)=0$$ $$mg + F_D = 0$$ From ...
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Why wouldn't the weight of an object affect the magnitude of the drag force on that object?

I ran into trouble again with a course about drag force on skiing. This is the question, and its explanation: Which of the following factors would not affect the magnitude of the drag force on an ...