Wikipedia:Reference desk/Archives/Science/2017 August 3

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

August 3

Term for the brain's ability to maintain stable vision?

Let's say a human is walking. As he is walking, his head is likely going to go up and down. However, the brain corrects this, so the vision would seem relatively stable. I think it's one reason why, when holding a camera while walking, the camera doesn't have that brain's ability so the result is a lot of shaking. 50.4.236.254 (talk) 02:19, 3 August 2017 (UTC)

Actually the main thing responsible for this ability is a brain mechanism that automatically redirects the eyes in a way that compensates for head rotations -- this is known as the vestibulo-ocular reflex. It is so automatic that we are generally not aware of it, but one way to see how important it is, is to close one of your eyes and then gently push on the eyelid of the other, moving the eye to the side a little bit. If you do this, you will see that the world appears to move sideways. The VOR is not the whole story, but it is the most important part. Looie496 (talk) 03:16, 3 August 2017 (UTC)

What's a VOR got to do with vision -- I thought it had to do with radio navigation? 2601:646:8E01:7E0B:8CEA:4A9:11B:99DA (talk) 06:24, 3 August 2017 (UTC)

The up down movement of the head while walking or running is a very important way the brain figures out how far away things are, but there's no point in having it intruding into the perception of objects themselves. Even with stabilization if a camera keeps moving around the place the picture is going to move around annoyingly because of parallax changes which you can't easily ignore since you are not moving. Dmcq (talk) 09:14, 3 August 2017 (UTC)

Irrelevant, off-topic discussion that doesn't contribute to inquiry
The following discussion has been closed. Please do not modify it.
The same IP asks questions about the brain. Dmcq doesn't direct to Google Scholar, which is just a search engine. 50.4.236.254 (talk) 11:37, 3 August 2017 (UTC) 'The same IP' is yourself. That is if you really do have a self and aren't some version of ELIZA. Dmcq (talk) 12:47, 3 August 2017 (UTC) https://en.wikipedia.org/wiki/Wikipedia:IP_addresses_are_not_people 50.4.236.254 (talk) 23:23, 3 August 2017 (UTC) Now your just being difficult for its own sake. Clearly, you're the same person who has been asking these questions. Stop it. --Jayron32 00:59, 4 August 2017 (UTC)

Tr8x4(P2) Leadscrew

For a Tr8x4(P2) Leadscrew[1], how many millimetres does the nut advance for one revolution of the screw? Covfefe beans (talk) 12:17, 3 August 2017 (UTC)

That's fairly trivial to figure out: the distance a screw advances (called the "lead") is always some whole number multiple (often just "1x") of the pitch (distance between threads) of the screw. See Screw (simple machine)#Lead and pitch for an explanation. --Jayron32 13:08, 3 August 2017 (UTC)

I believe that one is double start with pitch 2mm, and going around once will advance 4mm. But yes measuring is never a bad idea! Dmcq (talk) 13:25, 3 August 2017 (UTC)

"TR" is Trapezoidal thread form, first Number is the nominal diameter (8mm i guess) and the number after X is the pitch, which is ofcourse identical to the shaft movement in one revolution. This is however not a regular trapezoidal-threaded shaft, as by ISO TR 8 pitch is 1,5 (TR8X1.5) so this, with a pitch of 4mm, must be a double threaded shaft with 2 contour lines running around the diameter instead of the normal one! So this is not a ISO/regular part and you will probably get fitting thread nuts only from the same source!!

Because of the unusual pitch and double screw line i would not recommend buying/using it. If you aim for a faster shaft movement simply double the rotation frequency. Also naturally a double pitch (compared to the normal ISO one) means half the precision and rigidity you would expect form a shaft of that diameter! Last not least special parts are usually exponentially expensive. --Kharon (talk) 05:50, 4 August 2017 (UTC)

Jayron is saying lead is the amount of travel per revolution. You are saying pitch is the amount of travel per revolution. Who is right here? Covfefe beans (talk) 09:47, 4 August 2017 (UTC)

Read the sources and decide for yourself.--Jayron32 09:55, 4 August 2017 (UTC)

I'm well aware of the answer. I was just pointing out Kharon's mistake so that others reading the RD, or the RD archives, won't be mislead by the misinformation. Covfefe beans (talk) 10:24, 4 August 2017 (UTC)

Sorry, in case i wrote anything wrong. Btw. whats the meaning of Covfefe? --Kharon (talk) 04:51, 5 August 2017 (UTC)

See Donald_Trump_on_social_media#"Covfefe". Blooteuth (talk) 16:23, 5 August 2017 (UTC)

Israel Border Police equipment

• 
• 

What's the name of the this Israeli a) boat b) police car?--VideoCore (talk) 20:18, 3 August 2017 (UTC)

The car is probably an older model from Plasan. --Kharon (talk) 06:04, 4 August 2017 (UTC)