# 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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0answers
16 views

### Why are flat plates less drag than concave surfaces?

Why is B more drag than A? I think it's because the concave surface makes the fluid move backwards, while the flat plate does not.
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### Determining whether I hit the bed when jumping from a cliff [on hold]

For simplicity, assume a perfectly spherical object with uniform density falling from some height to a lake. How can I determine whether I hit the bed of the lake? Maybe this has something to do with ...
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### Why do we consider the viscous force to be tangential?

Is it that since it is a friction force, it needs to be tangential as other friction forces like kinetic friction and static friction forces are?
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### Will arrow from traditional longbow will be dangerous if it is falling from above?

Let's imagine commonly seen in movies and video games "rain of arrows". Archers shoot up to hit enemies behind the obstacles, for example. As Brittanica states: “The best longbows were made of ...
1answer
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### Why can't $U=b\mathbf{v} \cdot \mathbf{r}$ be considered a potential for the drag force ${\bf F}=-b {\bf v}$?

Consider the function $U(\mathbf{r},\dot{\mathbf{r}})=b\mathbf{r} \cdot \mathbf{v}=bx\dot{x}+by\dot{y}+bz\dot{z}$, where $b$ is the drag coefficient. Why can't this be considered as a potential energy ...
2answers
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### Resolve Drag into Vector Components

Assume you have a sphere travelling at a velocity of $30$m/s, at angle $30^\circ$ relative to the local horizontal plane. For the purposes of the below equations please ignore more complicated ...
1answer
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### Finding displacement by integrating forces that vary with velocity

I have a body that is being affected by forces, some of which are invariant ($F_i$) and some of which vary with velocity ($F_v(v)$). Given that $F=ma$ (where $F=F_i+F_v(v)$), how do I integrate this ...
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### Drag force as a function of shear & normal stresses

I would like to understand the relationship between the drag force of an object in a fluid and the microscopic interactions between the object and the fluid particles. Specifically, I would like to ...
1answer
28 views

### What's the “cause” of damping coeff. in springs?

What's the "cause" of damping coeff. in springs? Air resistance, friction?
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### An Interesting Physics Problem of Calculus [closed]

A skydiver of mass m=100 kg is making a delayed drop with an initial speed of $~v=0~$.Find the law by which the diver's speed varies before the parachute is opened if the air drag is proportional to ...
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### Deriving terminal velocity

In my book (Young and Freedman's University Physics) they derive terminal velocity where and use these steps: ...we must find the relationship between velocity and time during the interval before ...
2answers
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### Is the physics behind planetary travel simpler than atmospheric travel?

I've been watching a bunch of documentaries lately and had a question that I couldn't really figure out the answer to online. When spacecraft travel through space, are the equations and physics used ...
1answer
187 views

### Generating lift by Naruto running

"Naruto running" is running with your arms behind you (pictured above). Many characters in the Naruto series are superhuman and can run way faster than a normal human. I thought that they run like ...
2answers
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### Why can't we use air pressure to recharge an electric cars battery

If we use energy to accelerate a vehicle, a lot of that energy is lost to drag and friction, especially in an electric vehicle. Why can't we harvest some of that energy using an alternator and some ...
2answers
58 views

### Flight time of spherical bullet fired horizontally versus dropped vertically / effect of crosswind on spherical car

Would a spherical bullet fired horizontally from a musket stay aloft longer than a spherical bullet dropped from the same height? I know two similar questions have been asked (Will a bullet dropped ...
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### Friction at high speeds

I am reading a book which mentions that frictional force is not exactly proportional to the normal force at high speeds. Quoting: Once the bodies slip on each other frictional force is, $kN$. This ...
1answer
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### Is it possible to find $\mathbf{v}$ explicitly when $\mathbf{F}$ varies with $\mathbf{v}$?

I have the following problem (NO, this is not to ask for a solution to this problem). A block is placed on a plane inclined at an angle $\theta$. The coefficient of friction between the block and ...
2answers
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### Why is the velocity in the horizontal direction constant for 2D projectile motion?

For 2D projectile motion, why is the velocity in the horizontal direction constant? I learned that we neglect air resistance, but why? And isn't there horizontal acceleration at the beginning when ...
1answer
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### Damped harmonic oscillator's maximum displacement [closed]

I want to know the maximum displacement $x_0$ of a mass $m$ on a spring with spring constant $k$, in the case that the system is damped with damping constant $c$, and where the initial velocity $v_0$ (...
3answers
180 views

### Why is the drag force proportional to $v^2$ and defined with a factor of $1/2$?

$$Drag = \frac{1}{2}C_d \rho Av^2$$ I understand that the strength of the drag depends on the density of the fluid the body passes through, the reference area of the body, the drag coefficient, and ...
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### Effect of air resistance of the period of a pendulum [duplicate]

Does air resistance increase or decrease the period of a simple pendulum?
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### Calculate the kinetic friction velocity vector from the kinetic friction force in a simulation

I am doing (programming) a simple kinematic 2D simulation on blocks. The idea is that the block will have a force applied. 1) From the force and mass I calculate the the acceleration vector (will ...
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### Why is it easier to catch mosquitoes with your hand when your hand is wet?

Recently I've noticed that it's significantly easier for me to catch a mosquito with my hand if my hand is very wet (e.g. from having washed my hands and not yet dried them, or from being in the ...
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### High velocity mushrooms?

So y’all know meteoroites burn up in our atmosphere I’m looking for an equation or something that will allow me to calculate how fast a substance can move before it starts to burn up. Specifically I’m ...
2answers
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### Does air resistance have a greater affect on longer pendulums than shorter ones due to the greater exposure it has to air?

I'm thinking, because longer pendulums travel for a greater time period through the medium of air, air resistance will have a greater affect on the pendulum bob (and string) and so the angle the ...
1answer
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### Is Verlet method suitable for to solve projectile motion with quadratic drag?

Consider the following non-dimensional equations of projectile motion in presence of air resistance, I understand it can be numerically solved using the mid-point method, but can I also use Verlet ...
2answers
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### Projectile with air resistance from a given hight

Objects take same time to fall a given height independent of their horizontal speed when air resistance is ignored, is this also true when air resistance is not ignored? In presence of air resistance, ...
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### Why is the rudder of a ship shaped like a wing?

I don't understand why lift gives an advantage, it could be working the same even if it was just flat.
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### Drag Coefficient of a rounded nose cylinders

According to this page The drag coefficient of a rounded cylindrical bodies is given by this graph Then the drag coefficient of a cone for a half vertex angle ε is given by this graph. How can ...
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### Viscosity from terminal settling velocity of a sphere

I don't have an attempted answer to this question because I don't really know where to start. The Tip says to start from a force balance for the sphere, but I'm not sure on how to do that. I know ...
1answer
101 views

### How to find drag of a cylinder?

How can I find a drag on the cylinder placed in uniform water flow, if I know a velocity field around it?
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### Coefficient of drag past a cylinder

I have a lab assignment to determine a drag coefficient of a cylinder perpendicularly submerged in water. I have a measured velocity field and cylinder diameter. How can I find Cd? (I heard of a ...
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### At what speed in air would a solid object turn to plasma?

Just curious, friction can heat up what ever is moving. The faster something moves the quicker it heats up. Is it possible in the perfect scenario to turn a speeding solid object to plasma through ...
1answer
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### Which ball touches the ground first? Different explanations

Two balls with the same shape and volume but very different masses are dropped from the same height WITH air. The heavier ball should land first, but is it because of terminal velocity (see this ...
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### Does cross-sectional area affect the air time of a vertically thrown object?

Factoring in air resistance, I have two objects A and B of identical mass, however have different cross-sectional areas. A has a larger cross-sectional area than B. If I throw both objects directly ...
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### Derivation of the wind load formula

I am trying to derive the wind load formula: $F_d = \frac{1}{2} \rho v^2 A C_d$ in which I assume the drag coefficient to be equal to 1. My starting point is that the momentum of a rectangular wall ...
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### Where exactly does the drag force come from when using eddy currents?

I read the Wikipedia page on eddy currents and the explanation for braking confused me At the leading edge of the magnet (left side) by the right hand rule the counterclockwise current creates a ...
2answers
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### Does damping force depend on frame of reference?

I learn that damping force with regard to forced damped oscillations is given by F = -bv where is the velocity of the object measured from ground frame. Suppose we are in a frame which is moving with ...
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### Force applied by horizontal wind on object

Hello, I have a question for a project I'm currently doing: In a tunnel with no gravity, there is a constant wind blowing through. A sphere in the middle of the tunnel is completely motionless to ...
1answer
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### Calculating magnetic strength required to hold an objects weight + wind speed?

Note: I'm a bit new to this subject, so I'm looking for some general answers, ballparks, and direction to continue my research. Scenario: I have three electromagnets capable of X amount of holding ...
2answers
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### The force of wind on baseball

Does anyone know of an equation that I would be able to use for the force of wind acting upon a baseball? I am working on the projectile motion of a baseball with air and wind resistance. I have the ...