# 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.
0answers
25 views

### 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 ...
1answer
39 views

### 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?
1answer
64 views

### 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 ...
3answers
27k views

### Explanation that air drag is proportional to speed or square speed?

A falling object with no initial velocity with mass $m$ is influenced by a gravitational force $g$ and the drag (air resistance) which is proportional to the object's speed. By Newton´s laws this can ...
1answer
73 views

### 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
29 views

### 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
42 views

### 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 ...
0answers
23 views

### 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 ...
4answers
408 views

### How are orbits made stable?

I understand the concept of object staying in some orbit due to centrifugal force and gravity. However I do not understand how is orbit of a body like satellite or planet has perfect balance between ...
1answer
28 views

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

What's the "cause" of damping coeff. in springs? Air resistance, friction?
0answers
36 views

### 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 ...
2answers
90 views

### 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
156 views

### the different settling speed of two solid particles in fluid

In a container full of fluid A, which can be water or oil, I have two solid particles, both of which are of the same material. These two particles are of different size. One is bigger than the other ...
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 ...
1answer
32 views

### 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 ...
3answers
12k views

### Why does a sheet of paper fall slower than the same when rolled into a ball?

It depends on volume but both the sheet and the sphere have the same volume. Does surface area play any role here?
2answers
46 views

### 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 ...
1answer
102 views

### Forces in a body falling with air resistance

I would like to know why when a body falls with air resistance, we have that the drag caused by the air is $-kv$ and the acceleration is $-mg$. What I don't understand is how they both have the same ...
1answer
472 views

### Parachute jumping with air resistance

I need to write down a model for a man parachuting from a plane at a height $h$ above the ground, having a velocity $v_{\text{plane}}$. I've had a look at many models online and they all start saying ...
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 ...
0answers
39 views

### 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
57 views

### 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
36 views

### 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
32 views

### 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 $v_0$ (...
0answers
31 views

### 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 ...
2answers
742 views

### Falling book and paper

I've seen an experiment where a closed book with a piece of paper lying on its cover is dropped a short distance (the piece of paper is smaller than the book; the book's cover is parallel to the Earth'...
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 ...
1answer
29 views

### Effect of air resistance of the period of a pendulum [duplicate]

Does air resistance increase or decrease the period of a simple pendulum?
1answer
29 views

### 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 ...
1answer
36 views

### 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 ...
2answers
316 views

### Work done by air resistance

How can air resistance do work on a freely falling body on earth. then it's displacement is only due to gravity. I think Air resistance doesn't displace the body falling. So what is the meaning of ...
3answers
189 views

### 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 ...
1answer
86 views

### 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
77 views

### 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, ...
2answers
35 views

### 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
68 views

### 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 ...
3answers
1k views

### Drag - Dimensional Analysis / Buckingham $\pi$

I'm working on dimensional analysis and I'm having trouble. Here's a problem from my book I'm working on. I'm supposed to consider a small sphere experiencing acceleration due to gravity $g$. The ...
5answers
1k views

### How does a helicoper auto-rotate? The force of the air pushing on all blades would equal out. Wouldn't it?

So, I was learning about helicopter and how they auto rotate and I learned that when the engine fails the helicopter starts to fall and the air is thrown up at the blades which turns them like a ...
1answer
97 views

### Train Physics Simulation

It's my first time asking here so bear with me. I'm a computer scientist, and I'm working on a train simulator project. I'm having quite a difficult time understanding all the physics and formulas ...
2answers
10k views

### If starting speed is faster than terminal velocity then what?

If an object is say thrown down (vertically) at an initial speed that is faster than its terminal velocity, what would happen to that objects speed? Would it slow down?
0answers
31 views

### Davis formula application

So I stumbled upon the Davis formula for trains while doing some researches about my project but I don't know how to apply it (programmatically) : Let's say for example this variant : R'=1.3+\frac{...
0answers
33 views

### Fuel efficiency of supersonic planes

I stumbled upon an interesting plot; in particular, the dependence of wave drag on the Mach number: It is curious to see that the drag coefficient drops so abruptly in the supersonic regime, but I am ...
4answers
7k views

### Would a fast inter-stellar spaceship benefit from an aerodynamic shape?

Some (generous) assumptions: We have a spaceship that can reach a reasonable fraction of light speed. The ship is able to withstand the high energies of matter impacting at that speed. Given the ...
0answers
20 views

### Individual air molecule momentum exchange

Background: Looking at this illustration about solar radiation pressure on a perfect reflective surface, incident photon exchanges its momentum to the slanted surface which provides a reaction force ...
2answers
67 views

### How do you find the minimum height to open a parachute for a safe landing?

What concepts/formulas can be used to find the optimum/minimum release height of a parachute?
5answers
5k views

### What happens when the drag force exceeds the weight of an object falling into earth?

Let's say a meteor is coming towards earth. It's not accelerating, but it does have an initial velocity. This meteor is shaped so it has an insane amount of drag, enough to even exceed its weight (not ...
0answers
19 views

### 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 ...
4answers
68 views

### Why the book falls faster than a feather, dropped from the same height? [duplicate]

If I dropped book and feather from same height. Why book falls first, however book has more windage(air resistance), more area(square) than feather?
1answer
3k views

### How is the fall time for a parachute affected by the mass of the load?

Why do parachutes with a heavier load fall faster than a parachute with a lighter load?