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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124
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10answers
27k views

Why do spaceships heat up when entering earth but not when exiting?

Recently I read up on spacecrafts entering earth using a heat shield. However, when exiting the Earth's atmosphere, it does not heat up, so it does not need a heat shield at that point of time yet. ...
105
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6answers
24k views

Why is oil a better lubricant than water?

How come mineral oil is a better lubricant than water, even though water has a lower viscosity? When two surfaces slide over each other with a gap filled with a fluid, the different layers of the ...
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5answers
11k views

Why do archery arrows tilt downwards in their descent?

In the movies, arrows shot into the air rotate so that during the descent, the arrow head hits ground first. What is the source of this angular momentum? It would seem that the bow string exerts a ...
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6answers
13k views

Which ball touches the ground first?

This is a very well known problem, but I can't find an answer in the specific case I'm looking for. Let's consider two balls : Ball 1 weighs 10 kg Ball 2 weighs 1 kg Balls have identical volumes (so ...
39
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6answers
69k views

Could someone jump from the international space station and live?

Felix Baumgartner just completed his breathtaking free-fall skydiving jump from $120,000\,\text{feet} = 39\,\text{km}$ above the Earth, breaking the speed of sound during the process. I was wondering ...
38
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5answers
9k views

Why does a weather vane arrow point in the direction of the wind?

It seems that a weather vane will rotate in order to minimize energy and thus orient itself parallel to the wind. What I do not understand is why it is implied that the weather vane arrow should ...
38
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5answers
28k views

Why do heavier objects fall faster in air?

We all know that in an idealised world all objects accelerate at the same rate when dropped regardless of their mass. We also know that in reality (or more accurately, in air) a lead feather falls ...
37
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7answers
15k views

Why is it apparently not dangerous to fire a shotgun (such as when “skeet shooting”) into the air?

If you fire a gun or rifle into the air, whether straight up or at an angle, as I understand physics, a metal projectile will gain surprising momentum on its way down again, more than capable of ...
33
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3answers
7k views

If we threw a baseball from the ISS, could we deorbit the ball?

Clearly this is a hypothetical question. Say we bring a star baseball player into NASA, prep them appropriately for a mission in space, and fly them up to the International Space Station. They go on ...
31
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3answers
13k views

What are the precise statements by Shouryya Ray of particle dynamics problems posed by Newton which this news article claims have been solved?

This recent news article (here is the original, in German) says that Shouryya Ray, who moved to Germany from India with his family at the age of 12, has baffled scientists and mathematicians by ...
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2answers
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How long until we fall into the Sun?

As a planet moves through the solar system, a bow shock is formed as the solar wind is decelerated by the magnetic field of the planet. Presumably the creation of this shock wave would cause drag on ...
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5answers
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Does a person inside a falling bus fall to the front of it?

So I was watching Final Destination 5 and something caught my attention. There's a part where a bridge collapses and everything falls apart, so there's this bus that has a person inside (unaware of ...
18
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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 ...
18
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2answers
2k views

Why do flat objects land softly?

I noticed that if you drop a flat surface, parallelly from a relatively low height, onto another, the impact is almost cushioned. What is happening here? Is this to do with the air, especially near ...
18
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5answers
7k views

Would a fast interstellar 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 ...
17
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1answer
277 views

Why is the top surface of a ceiling fan more dusty than the bottom?

Top surface of a ceiling fan ( that hasn't been cleaned for a long time) The bottom surface The top surface seems to be way more dusty than the bottom. I reason that it doesn't have anything to do ...
16
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4answers
50k views

After what speed air friction starts to heat up an object?

I understand that air friction cools off an object at low speeds. For example, if you blow on a spoon of hot soup, it cools off. Or if you swing a hot frying pan in the air, it cools off faster. But ...
16
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5answers
12k views

What causes a soccer ball to follow a curved path?

Soccer players kick the ball in a linear kick, though you find it to turn sideways, not even in one direction. Just mid air it changes that curve's direction, i.e., it swings, as footballers say. Is ...
16
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5answers
12k views

Why aren't airplanes like golf balls?

Ok this is a silly question but here it goes Although it is good to have a laminar flow of the air around the object for low drag but the laminar flow is prone the phenomena called separation (sounds ...
16
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1answer
318 views

How fast would a truck have to go to pull a pedestrian onto the road? [closed]

Let's suppose a pedestrian P is walking or standing next to a highway. Suppose a truck T will drive by the said pedestrian at speed V leaving distance L between the two. Assuming L is a reasonably ...
15
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1answer
3k views

Can I move an oil tanker?

Let's say that I'm standing at the edge of a basin made of concrete. This basin is filled with salt water and a ship floats on the water close to the edge of the basin. The ship is neither anchored ...
14
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7answers
3k views

What does an undefined formula in physics mean?

I am trying to figure out how undefined formulas in mathematics relates to physics. Take the following formula for terminal velocity. $$V_\text{terminal} = \sqrt{ mg \over{c \rho A}} $$ Say we have ...
14
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7answers
10k views

Flat throw vs 45 degree throw of a ball

Why does my sports coach tell me that when I'm fielding I should throw the baseball 'flat' to get the maximum distance? I thought from physics that you get the most distance from throwing at a 45 ...
14
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3answers
3k views

Which ball falls faster, the cool one or the hot one?

Suppose we're on the top of the Tower of Pisa (or a larger version of it) with two identical cannonballs. We heat one up (say, to 200 degrees Celsius, or some other high temperature before it starts ...
14
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3answers
1k views

Would an airplane flying through superfluid helium experience lift and drag?

Would an airplane flying through superfluid helium experience lift and drag? The airplane is presumed cold enough to not heat up the helium.
14
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2answers
1k views

Do celestial objects experience drag from the near vacuum of space/does the near vacuum have a mean velocity?

For instance do the planets around the sun experience drag from the near vacuum of space? Or do the (hydrogen) atoms in interplanetary space have a mean velocity near orbital speeds, such that object ...
14
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5answers
9k views

How do I calculate the distance a ship will take to stop?

I am a River Pilot and drive ships for a living. These ships are very large and range up to 160,000 Metric Tons. I am trying to figure out how to calculate the distance to stopping. I have a basic ...
13
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4answers
5k views

Why doesn't a tied balloon behave like a pendulum?

It is well known that a tied weight will oscilate under the effect of gravity if left from aside, like a pendulum. However, if we tie a helium balloon to the ground from and left it form the floor (...
13
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4answers
31k 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 ...
13
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2answers
12k 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?
12
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6answers
14k views

Why would a fat skydiver fall first in free fall?

I was having one of those obnoxious conversations with a friend where he was arguing that a fat skydiver would reach the ground faster than a skinny skydiver. To me it seemed as obvious that the world ...
12
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2answers
3k views

Why do co-rotating vortices coalesce, but not counter-rotating ones?

In studying the aerodynamics of modern aircraft equipped with high-lift devices, I have discovered that quite a number of distinct trailing vortices are present in the immediate wake of an airplane in ...
12
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2answers
7k views

Will a bullet dropped and a bullet fired from a gun horizontally REALLY hit the ground at the same time when air drag is taken into account?

In a world without air, I understand they definitely would. However, with drag taken into account, I think they wouldn't. Since the drag force varies proportional to the square of speed (ignoring the ...
12
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1answer
195 views

Physics of air flow in Kipchoge's sub-2:00 marathon

Yesterday Eliud Kipchoge became the first human to run a marathon distance in under two hours. Part of what allowed him to do it seems to have been that he had pacers running along with him to break ...
11
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1answer
4k 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 ...
11
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5answers
2k views

Do objects have a tendency to fall in their most aerodynamic position?

In one of my physics classes, we are using slow motion video to analyze the falling motion of an object and then find out the drag coefficient of that object etc. I noticed while doing this that if I ...
11
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4answers
17k views

Acceleration of two falling objects with identical form and air drag but different masses

I have a theoretical question that has been bugging me and my peers for weeks now - and we have yet to settle on a concrete answer. Imagine two balloons, one is filled with air, one with concrete. ...
11
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1answer
1k views

How would you swim in inviscid water?

The viscosity of water creates drag on swimmer's body so its effect is to slow down the swimmer. However the viscosity seems to be essential for pushing the water backwards by the swimmer's arms and ...
9
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2answers
5k views

How much more efficient is a road bike than a mountain bike? [closed]

What would be a good estimate on the difference of efficiency between a road bike and a mountain bike? A number of links cite all the usual reasons: thinner tires, better aerodynamics... But I'm ...
9
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5answers
8k views

What factors determine the coefficient of friction?

I am doing a physics class online, and have a test next week and it is pretty hard to understand a physics class when you do not have the privilege of asking questions as often as i would like. So i ...
9
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2answers
25k views

What shape has the highest drag coefficient?

This image from NASA illustrates drag coefficients for several shapes: It is generally accepted that some variation of the teardrop/airfoil shape has the lowest drag coefficient. I was wondering ...
9
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1answer
19k views

Terminal velocity of two equally shaped/sized objects with different masses?

I've tried doing research on this and there are some similar questions. However, they have slightly different scenarios and to make sure I understand things perfectly, I wanted to word it into my ...
9
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2answers
6k views

Could some design of a propeller be used in both air and water?

Propellers in water are smaller in diameter. They also move more slowly. On the other hand, aircraft propellers are larger in diameter, have narrower blades and operate at very high speeds. An ...
9
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3answers
188 views

Did Newton know or assume that planetary (extraterrestrial) space was frictionless vacuum-space?

For a correct calculus of the perpetual orbital motion of planets as determined by Newton’s laws of gravitation, frictionless motion through interplanetary vacuum space would have been a prerequisite. ...
9
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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 ...
8
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3answers
8k views

Why does tossing a coin in a train and on a train differ?

Suppose that I am inside of a moving train. I have a coin in my hand and I am standing still. If I toss this coin straight up, it will fall back into my hand. Now, suppose that I am on that moving ...
8
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9answers
2k views

Physics Paradox about Newtons Second Law $F=ma$

If force equals mass times acceleration, wouldn't a basketball dropped from the top of the Eiffel tower exert the same force on the ground as a basketball dropped a foot off the ground? They both have ...
8
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2answers
2k views

What is the terminal velocity of a sheep?

Inspired by this question on Gaming.SE Using actual in-real-life physics, what would the terminal velocity of a sheep actually be? I would assume it would be around 50m/s, but I might be wrong. ...
8
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1answer
2k views

What is the Davis Equation and why is it used in a Train Simulator?

I have been trying to understand how Microsoft Train Simulator works and people seem to use some Davis equation to calculate friction. So my questions are: What is it? Why do they use it? Are there ...
8
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2answers
612 views

Theory behind the relationship between the mass of a cylinder and the time taken for it to roll down an incline - air resistance?

I conducted a simple experiment where I tried to find the relationship between a cylinder's mass and its time taken (or average speed or acceleration, which can be easily derived from the time & ...

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