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.
Questions tagged [drag]
1209 questions
127
votes
10 answers
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. Why is this so? I know then when entering earth,…
QuIcKmAtHs
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109
votes
6 answers
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 fluid are dragged at different speeds. The very top…
DK2AX
- 4,860
72
votes
9 answers
Why do fans spin backwards slightly after they (should) stop?
Today, I've decided to observe my PC fan as I shut the computer down. The fan slowly lost angular momentum over time. What I've found really interesting is the fact that the momentum vector change did not stop at the zero vector, but instead flipped…
Captain Trojan
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69
votes
7 answers
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 force directly in line with the arrow.
lamplamp
- 1,668
53
votes
7 answers
Solving the helicopter hanging cable problem through differential analysis
The above problem is taken from the 2014 $F=ma$ contest.
This question generated a great deal of controversy. At least two test takers challenged the
answer, one who even tried to do the experiment. I’m told that several different…
Neox
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41
votes
6 answers
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 if the next step could be jumping from the…
Reactgular
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41
votes
5 answers
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 much faster than a duck's feather with exactly the…
Simd
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40
votes
6 answers
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 Ball 1 is much more dense)
Balls have identical…
FlipFlapFlop
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38
votes
6 answers
How can a Kestrel hover in the wind?
Kestrels are birds of prey commonly found in Europe, Asia, Africa, and the North America. They belong to the falcon family but have a unique ability to hover in the air. You can find a whole bunch of videos (See 1,2,3,4, for example) about these…
AlphaLife
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37
votes
8 answers
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 killing a grown human being, not to mention small…
user12989506
- 503
37
votes
5 answers
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 point in the direction of the wind.
I do not…
user391339
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33
votes
3 answers
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 a spacewalk with a baseball, and at the apoapsis…
Marsh
- 453
32
votes
3 answers
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 solving two fundamental particle dynamics problems…
Zev Chonoles
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29
votes
9 answers
Effect of drag on projectile flight time - simple solution?
I saw a question like this in an AS-level physics paper (consisting of 40 questions given to ~17-year-olds, with a 75-minute time limit):
Two identical balls, x and y, are thrown up from the earth's surface with the same velocity. x is thrown in…
Jao Bai Dun
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28
votes
2 answers
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 the planet, certainly in the direction of orbit…
tpg2114
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