Wikipedia:Reference desk/Archives/Science/2008 October 4

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October 4

Seeing bullets (with no tracers) streak through the air using IR goggles

Would bullets (with no tracers) be very visible if you were to observe them using IR goggles? —Preceding unsigned comment added by ScienceApe (talk • contribs) 16:38, 4 October 2008 (UTC)

There are two main types of IR goggles and cameras. There are night vision ones that work user near-IR (nearer to visible light, that is) which work by capturing the reflected IR in the same way that visible light is used. They often come with an IR light that illuminates the area with IR so it can be seen (if you watch night vision video you can often see that there's a light shining on the middle of the image and around the edge is much darker). There is then thermal imaging which uses far-IR and captures IR emitted directly by the objects before of their heat. I believe bullets are fairly warm, so would show up well on thermal imaging, but I see no reason why they would show up any better than anything else under night vision. --Tango (talk) 16:57, 4 October 2008 (UTC)

Yes, very visible. Well, the thermal imaging ones at least, as Tango said.

edit: You may want to consider these things though:

• A bullet is small and fast, so seeing it will be really hard using goggles, a camera will have a better chance.
• As noted in the link, the bullet will cool down in flight.

- Dammit (talk) 22:17, 4 October 2008 (UTC)

The night vision goggle (NVG) type can see emitted IR as well as reflected - but the higher frequencies that NVG's are sensitive to are not normally emitted in much quantity by things that are merely warm. However, a piece of "red hot" steel is obvious even to the naked eye (that's why we call it "red" hot). Hence, something that's just a little cooler than red hot would be highly visible by radiated IR in NVG's. The lower frequency detectors in InfraRed cameras (such as you might find on a combat helicopter, drone or fighter/bomber) are able to see radiated IR across a wider range and are sensitive enough to see things that are just a fraction of a degree above their environment - you can see warm 'tracks' left by a vehicle driving by for example! I've worked a lot with both kinds of sensor - you can't see regular bullets in flight with either of them - there just isn't enough light (IR or otherwise) and it's not there for long enough. Also, the resolution of both NVG's and IR cameras is nowhere near fine enough to pick up something that small at a distance. But tracer is highly visible to both because it produces a lot of visible light (which the NVG can see) and the cloud of combustion products is large enough and hot enough for the IR camera to pick up. The 'rangerats' stuff that User:Dammit provided is deceptive. Firstly they aren't using regular NVG's or military IR - they are using some kind of very fancy IR camera that's specifically designed for measuring temperature rather than for seeing well at night (this is obvious from the 'false color' images on their site - military stuff doesn't use false color - the images are invariably monochromatic, and typically green). Secondly they say that the bullet was only visible fairly briefly just as it left the barrel of the gun - a fraction of a second later, it was too cool to register on their equipment. SteveBaker (talk) 11:56, 6 October 2008 (UTC)

Please read better before of calling something deceptive. The only thing fancy about the camera used is that it is a high speed one, other than that it's not all that different from thermal imaging goggles. Also they don't write that the bullet was only visible briefly, in fact they could have followed it right to the target if the camera could pan fast enough (see the link to the shot apple on the article). They just used a static camera pointed at the muzzle and selected the first image where the bullet came out of the gas cloud (before that bullet it was not visible). - Dammit (talk) 23:40, 8 October 2008 (UTC)

Is this understandable?

Quite confusing IMO.

Our sail car is trapezoidal with two horizontal extensions, one on each side of the car in the back. The extensions are created using four straws. Two are linked together to form what appears to be one long straw in the very back (creating the rear base of the trapezoid as well), so that only very ends of the 'straw' are part of the extension. It holds two wheels on each extension, both (wheels) kept from sliding by two pins placed beside each wheel, the pins being stuck into the straw. The other two straws are on opposite sides of the car and in front of the rear straw. They support the wheels as well (the support pins are stuck through them after being stuck through the rear straw), but they bend towards the front of the car upon clearing the extensions. These straws bend upon reaching the front, creating the smaller (shorter) top (front) base of the trapezoid by connecting at the center of the front base. The front ends of the straws then hold two more wheels near the bent area. Right at the bend of each of the two front straws are two more straws are pinned to each one of the straws just aforementioned. These two straws converge and meet at the midpoint of the rear straw.

Roughly halfway between the extensions and the midpoint of the rear straw are straws extending vertically upwards. These straws are connected to a sail. The sails is bent inwards and is supported by a crossbeam at the top.

Rest assured, for the prototype actually worked.

--hello, i'm a member | talk to me! 22:21, 4 October 2008 (UTC)

Clarification is needed here. Is this native English language or a translation? (For that matter, please provide proper attribution when quoting extensive text on a GFDL site such as Wikipedia - who said that, where?)

And in particular, what does "straw" mean in context? Drinking straw, wheat straw, something else? Once you attribute that quote, we may be able to shed some light. Franamax (talk) 05:11, 5 October 2008 (UTC)

It seems to be some kind of little toy made with drinking straws. To answer the question: yes, this text is confusing. I got lost in the first sentence because I could not visualise the "sides" and the "back" of the trapezoid. A diagram would help. Itsmejudith (talk) 15:44, 5 October 2008 (UTC)

Is there any way I can clarify the passage? 'Front' and 'back' are arbitrary positions (they were defined on a whim...doesn't really matter too much) and yes, those straws are drinking ones. --hello, i'm a member | talk to me! 15:57, 5 October 2008 (UTC)

I second Itsmejudith...a diagram would help immensely. Even a very simple sketch would clarify what is where relative to what else. Alternately, a more technical diagram could have labeled parts replace this entire paragraph! DMacks (talk) 16:09, 5 October 2008 (UTC)

Assuming that I have a diagram, would this passage still be confusing? I know my question isn't all that answerable... --hello, i'm a member | talk to me! 16:28, 5 October 2008 (UTC)

The description is confusing and ungrammatical in places. It sounds like a first draft. In the fourth sentence, it's not clear what the pronoun "It" refers to. Perhaps if the text said "The rear axle," with that axle defined by what straws it was made of, all would be clearer. In the fifth sentence, instead of "in front of the rear straw" it should say "at the front of the trapezoid" to give a point of reference. In the sixth sentence replace "they" with an explicit declaration of what is referred to. In the 7th sentence, it is not clear in what direction the front straws bend: is the outside end of a front straw closer to the rear, or farther from the rear than the center of the front line of the trapezoid? In the 8th sentence, "the bent area" is undefined. The 9th sentence is vague and confusing, and contains an extra "are." If the front 2 wheels are on straws which are bent, then are their axes not parallel to the axes of the rear wheels? It sounds like the front wheels point at an angle, which would make it difficult for the device to move forward without dragging the front wheels, which would want to roll in different directions from the back wheels and each other. Sentence 11 does not specify which straws are "the extensions" it refers to: front, back, or all four? How many straws point upwards in sentence 11, and where are they located in the trapezoid? Sentence 12: Specify the arrangement of the sail. Sentence 13: "Bent inwards" is vague. To move forward in a wind, the sail would need to be parallel to the rear axle to maximize thrust from wind coming from the rear, or at some lesser angle such as 45 degrees to take advantage of side winds and produce forward movement. Sentence 14: It "worked?" Even a crackerbox would move in a strong wind. How fast did it move in what speed of a wind coming from what direction? Edison (talk) 20:44, 5 October 2008 (UTC)