## Search found 709 matches

Wed Oct 06, 2010 3:55 am UTC
Forum: Science
Topic: Really Long Stick
Replies: 21
Views: 2985

### Re: Really Long Stick

Spoiler'd for pedantry Actually, speed of sound in a material is inversely proportional to the square root of density, for a given stiffness. That means that a higher density will cause a lower speed of sound. The equation for speed of sound in solids is found here . The reason most people think tha...
Tue Oct 05, 2010 5:47 pm UTC
Forum: Science
Topic: Facepalm TV / Doing It Wrong
Replies: 553
Views: 62172

### Re: Facepalm TV / Doing It Wrong

In regard to the colliding trucks question, the question should really be whether driving two trucks at 80mph into each other the same as driving one truck 160mph into a stationary truck. Introducing a brick wall into one system is just confounding the situation. 160^2 = 25600 > 2*80^2 = 12800. The...
Mon Oct 04, 2010 2:55 am UTC
Forum: School
Topic: Have you dropped a class because you had too many?
Replies: 10
Views: 2218

### Re: Have you dropped a class because you had too many?

I've always been confused about credit hours in the US Universities. I assumed it was how many hours of class you have per week, but since I have 31 and you dropped to 12, that's probably not right. How many credit hours is one half year or full year course? You're in 31 hours of class a week? That...
Wed Sep 22, 2010 6:03 am UTC
Forum: Science
Topic: Can you swim in a superfluid?
Replies: 26
Views: 4737

### Re: Can you swim in a superfluid?

Correct. I didn't mean to imply that lift is possible in an actual inviscid fluid, just that the lift on a body in a viscous fluid can be calculated using inviscid theory. I include the Kutta condition as part of inviscid theory, since it's pretty much a requisite for getting any useful data out of ...
Tue Sep 21, 2010 8:48 pm UTC
Forum: Science
Topic: Can you swim in a superfluid?
Replies: 26
Views: 4737

### Re: Can you swim in a superfluid?

When you study basic aerodynamics, you work with inviscid fluid mechanics, and you just sort of ignore things like D'Alembert's Paradox. You can quite easily do things like calculate the lift or drag of a body in an inviscid flow, because viscosity effects operate primarily in the boundary layer. Y...
Fri Sep 17, 2010 4:35 am UTC
Forum: Science
Topic: Current Sources in Series
Replies: 5
Views: 4890

### Re: Current Sources in Series

Ideal current sources and ideal voltage sources are imaginary, unphysical things. Asking what happens when you put two different current sources in series is like asking what happens when an unstoppable object hits an immovable wall.
Sun Sep 12, 2010 11:17 pm UTC
Forum: School
Topic: Hard work vs. Smartishness
Replies: 247
Views: 38531

### Re: Hard work vs. Smartishness

TheKrikkitWars wrote:being a relatively gifted "wet" chemist

OT, but the combination of this sentence with your avatar makes for an amusing mental image.
Sat Sep 11, 2010 5:55 pm UTC
Forum: School
Topic: Impact of Eagle Scout. (should i continue or not?)
Replies: 27
Views: 4521

### Re: Impact of Eagle Scout. (should i continue or not?)

I'll just point out that, being an Eagle scout, beyond part time jobs, it's kind of quite worthless. Actually, it's come in quite handy when interviewing for engineering positions. Most interviewers will at least mention it, and those who are familiar with the process may ask about your project, et...
Wed Sep 08, 2010 4:02 am UTC
Forum: Science
Topic: Reducing the effects of acceleration on the human body
Replies: 123
Views: 16907

### Re: Reducing the effects of acceleration on the human body

Here's some actual data (from J Aviat Med. 1958 Jun;29(6):433-7. Protection against acceleration forces in animals by immersion in water. MARGARIA R, GUALTIEROTTI T, SPINELLI D.): -8 out of 10 rats survived a brief acceleration of 1000g while submerged in water, while nearly 100% died during a brief...
Mon Sep 06, 2010 2:33 am UTC
Forum: Science
Topic: Direction of electric field {simple problem}
Replies: 7
Views: 2242

### Re: Direction of electric field {simple problem}

Poster above is right. The direction of an electric field is the direction of the force on a positive charge.
Sun Sep 05, 2010 2:45 pm UTC
Forum: Science
Topic: Does my presence significantly alter air pressure?
Replies: 17
Views: 2490

### Re: Does my presence significantly alter air pressure?

Call these guys. I'm sure they'll be glad to conduct a full scientific investigation.
Fri Sep 03, 2010 4:16 pm UTC
Forum: Science
Topic: Reducing entropy in unknown systems
Replies: 7
Views: 1748

### Re: Reducing entropy in unknown systems

But if it's at a negative temperature already...
Fri Sep 03, 2010 6:13 am UTC
Forum: Science
Topic: Reducing entropy in unknown systems
Replies: 7
Views: 1748

### Re: Reducing entropy in unknown systems

BlackSails wrote:Reduce its temperature and size.

Not entirely fail-safe.
Sun Aug 29, 2010 3:39 am UTC
Forum: Science
Topic: Peaceful, but Mad, Uses of Nuclear Weapons
Replies: 76
Views: 7695

### Re: Peaceful, but Mad, Uses of Nuclear Weapons

Nuclear weapons are not roadside IEDs. They are not designed to foil bomb technicians. Rather, they are designed not to go off unless commanded, to be stable for long periods of time, and to be maintainable.
Sun Aug 29, 2010 3:18 am UTC
Forum: Science
Replies: 21
Views: 2965

### Re: Advice on career choice

People with a BSc in physics end up in a wide verity of places, including engineering. Engineers are mostly hired to do engineering. So, if you want a good shot at an engineering job, do an engineering degree. If you want to keep your options open, and have the option of going the academic/scientis...
Thu Aug 26, 2010 5:53 am UTC
Forum: School
Topic: Do you guys think I should drop orgo?
Replies: 22
Views: 3220

### Re: Do you guys think I should drop orgo?

No one will care about a single W on your record, except maybe you. If I were you, I would stay enrolled in the class. Your schedules are only going to get more difficult as the semesters roll by, so you might as well take a hard class now to get it out of the way. If it turns out that you absolutel...
Wed Aug 18, 2010 7:20 am UTC
Forum: School
Replies: 344
Views: 60145

### Re: Reactions to your Major

I'm an aerospace engineer, so in addition to the usual responses, I also get "So you want to work for NASA?" It's like they've never heard of the entire aerospace industry. Who do they think designs airplanes?
Wed Aug 11, 2010 3:09 am UTC
Forum: Science
Topic: Female disinterest in STEM
Replies: 86
Views: 9879

### Re: Female disinterest in STEM

Many doctors don't work with other doctors. They don't have to present their ideas to other doctors and be judged by other doctors. They don't even have to defend their thesis in front of other doctors. What this means is that even though the profession may have been a boys' club, an individual fem...
Tue Aug 10, 2010 1:33 am UTC
Forum: School
Topic: Getting a Dog During College
Replies: 14
Views: 2635

### Re: Getting a Dog During College

not good at these things wrote:There are these miniature dotsons that are just cute little dogs...

Dachsunds (pronounced dock-sin). They're great little dogs, even purebred.
Sun Aug 08, 2010 10:43 pm UTC
Forum: School
Topic: Engineering school vs general science/liberal artsy?
Replies: 10
Views: 2234

### Re: Engineering school vs general science/liberal artsy?

These are definitely questions you should be asking before you decide on a college. You want to make sure your college will fulfill your academic needs. The answers are going to vary substantially between different colleges. Here's what you'll need to do: ⋅ Go to the websites of the progra...
Tue Jul 27, 2010 6:55 am UTC
Forum: Science
Topic: Propellers and rotors
Replies: 22
Views: 6072

### Re: Propellers and rotors

A lot of people are trying to draw a distinction between lift due to a pressure differential and lift due to pushing air downward. This is a false dichotomy. Think of it this way: there are two ways that the air and rotor blade interact: viscosity and pressure. Viscosity and Why I'm Ignoring It Visc...
Thu Jul 22, 2010 5:32 am UTC
Forum: Science
Topic: Charge Sensor
Replies: 5
Views: 1007

### Re: Charge Sensor

A voltmeter shouldn't have to touch the circuit itself to measure voltage. Just placing the leads close to wires on either side of the capacitor should do.
Mon Jun 28, 2010 5:23 am UTC
Forum: Science
Topic: The STEM Job Prospects Thread
Replies: 5
Views: 743

### Re: The STEM Job Prospects Thread

It's my experience that those positions are all only posted for show, as a legal precaution, and that any given position is only available or granted after successfully impressing upon someone who is hiring that you are fit for the job, at which point, a job is created for whom the requirement to a...
Mon Jun 28, 2010 2:03 am UTC
Forum: Science
Topic: The STEM Job Prospects Thread
Replies: 5
Views: 743

### The STEM Job Prospects Thread

I see a lot of articles like this one lamenting the lack of science jobs (and about as many articles lamenting the lack of scientists, but I suspect that's BS), but I rarely see anything with hard numbers from specific fields. To satisfy curiosity, I invite everyone to submit their own experience in...
Sat Jun 12, 2010 3:20 am UTC
Forum: School
Topic: IB Physics
Replies: 13
Views: 1821

### Re: IB Physics

Rwm28juni wrote:Rocket Science (or whatever it's called)

Aerospace Engineering
Mon Jun 07, 2010 12:48 am UTC
Forum: Science
Topic: Estimating Damage due to High-ISP Rockets?
Replies: 8
Views: 1804

### Re: Estimating Damage due to High-ISP Rockets?

For a rough estimate, I would start by making a few wild-ass guesses: ⋅ Damage is proportional to energy flux of the exhaust ⋅ The energy stays mostly at ground level. ⋅ Some other assumption I'm probably missing Energy flux of the exhaust stream is \frac{1}2\dot{m}v^2 ...
Fri Jun 04, 2010 11:42 pm UTC
Forum: Science
Topic: Is the psychobabble on Frasier convincing?
Replies: 19
Views: 3203

### Re: Is the psychobabble on Frasier convincing?

If you're a geek/freak/nerd/dork: Do you think I'm wrong about The Big Bang Theory ? Complaints spoilered: Even as an engineer, I can tell that a lot of the science on the show doesn't make sense, especially the easter eggs. For example, in one episode, there's a very simple circuit and tra...
Wed Jun 02, 2010 12:27 pm UTC
Forum: Science
Topic: Voltage and Current
Replies: 6
Views: 728

### Re: Voltage and Current

I've seen a textbook on hydraulics that suggested developing an intuition for fluid flow by comparing it to electricity. This was for engineering students who presumably had already taken E&M and Circuit Analysis, and therefore already had a good intuition for electricity. Different strokes, I g...
Mon May 31, 2010 5:47 pm UTC
Forum: Science
Topic: Extension of a Spring Due to Gravity
Replies: 11
Views: 2093

### Re: Extension of a Spring Due to Gravity

JWalker wrote:Since we stretched this thing a distance d, the spring potential energy is [imath]U_s=\frac{1}{2}kd^2[/imath]

That only works for a uniformly stretched spring. For a spring supporting its own weight, the top will be more stretched than the bottom, because it's supporting more weight.

EDIT: Ninja'd
Sat May 29, 2010 9:12 am UTC
Forum: Science
Topic: Simulation of a bending plant stem
Replies: 17
Views: 1882

### Re: Simulation of a bending plant stem

I'd love to see video of the final product in action, if that's possible.
Sat May 29, 2010 3:23 am UTC
Forum: Science
Topic: Extension of a Spring Due to Gravity
Replies: 11
Views: 2093

### Re: Extension of a Spring Due to Gravity

I've never seen this proof anywhere, but it is a neat little result. I suggest you prove it yourself.
Fri May 28, 2010 8:27 pm UTC
Forum: Science
Topic: Simulation of a bending plant stem
Replies: 17
Views: 1882

### Re: Simulation of a bending plant stem

I would approximate the stem as a series of rods connected by rotational springs and dampers. To make it look right, fit a spline to the points given by the spring/damper simulation. This would be easiest in 2D, but could be used for 3D as well.
Fri May 28, 2010 4:05 am UTC
Forum: Science
Topic: Simulation of a bending plant stem
Replies: 17
Views: 1882

### Re: Simulation of a bending plant stem

Is this meant to somewhat-accurately simulate bending, or just give a superficially plausible shape for the stem? Is this a dynamic simulation, or a static one?
Sun May 23, 2010 6:31 am UTC
Forum: Science
Topic: Temperature and velocity
Replies: 2
Views: 1249

### Re: Temperature and velocity

Temperature is, as I've been told, the average kinetic energy of a particle in a sample of a substance. Only for an ideal gas. A more general definition involves the amount of entropy added during heat transfer and is found here . So how are they mathematically related? Are the velocities of partic...
Fri May 14, 2010 5:59 am UTC
Forum: Science
Topic: High-strength magnetic fields
Replies: 12
Views: 1894

### Re: High-strength magnetic fields

Sir_Elderberry wrote:I'll pop in to note that an electric field wouldn't work at all if the metal has no net charge.

An electric field applied to a neutral piece of metal will induce a dipole in the metal, which can result in a net force on the metal.
Fri May 14, 2010 1:02 am UTC
Forum: Science
Topic: public misconceptions
Replies: 1073
Views: 149978

### Re: public misconceptions

you can be sued for accidentally raising GMO crops just by collecting seed pollinated by your competitor 10 miles away, even assuming that it doesn't have any other detrimental effects. If you are referring to Monsanto v. Schmeiser, it's pretty clear that Schmeiser intentionally cultivated herbicid...
Tue May 11, 2010 6:36 pm UTC
Forum: Science
Topic: Does the speed of sound vary depending on the intensity?
Replies: 5
Views: 985

### Re: Does the speed of sound vary depending on the intensity?

The speed of sound is dependent on air pressure. And guess what, sound is a pressure wave. Actually, for an ideal gas (which air approximates very well at STP), the speed of sound depends only on temperature. Temperature does change within a sound wave, but not much, as long as the wave is of reaso...
Sun May 09, 2010 4:12 pm UTC
Forum: Science
Topic: IB Chem SL review (redox, mass spec and more!)
Replies: 14
Views: 3662

### Re: IB Chem SL review (redox, mass spec and more!)

Biodiesel makes use of plants' ability to fix atmospheric carbon by photosynthesis. Many companies and individuals are now using biodiesel as a fuel in order to reduce their carbon footprint. Biodiesel can be synthesized from vegetable oil according to the following reaction: vegetable oil+3 me...
Sat May 08, 2010 12:50 am UTC
Forum: School
Topic: Calculus in engineering education
Replies: 10
Views: 1753

### Re: Calculus in engineering education

Can I ask what department you worked in? I hadn't really been thinking about numerical methods but that makes sense. But don't you still need a pretty solid understanding of the calculations in order to use them? Or can you really just get by with running built-in functions? Ideally, you have a good...
Fri May 07, 2010 10:01 pm UTC
Forum: School
Topic: Calculus in engineering education
Replies: 10
Views: 1753

### Re: Calculus in engineering

I'm still an Aerospace Engineering undergrad but I have some "real world" experience from co-oping and research. One thing I've considered is that perhaps in real life mechanical engineering problems the systems are not that much more complicated than they are now. Can the distribution of ...