# Crappy science instruction **URL:** \ **Category:** The BBQ Pit\ **Created:** [October 25, 2012, 3:24pm UTC](https://boards.straightdope.com/t/crappy-science-instruction/638830 "2012-10-25T15:24:51Z")\ **Posts on this page:** 7\ **Page:** 3
**Author:** ![Cheshire\_Human](https://avatars.discourse-cdn.com/v4/letter/c/5f8ce5/32.png) [@Cheshire\_Human](https://boards.straightdope.com/u/Cheshire_Human)\ **Post date:** [October 29, 2012, 2:04am UTC](https://boards.straightdope.com/t/crappy-science-instruction/638830/41 "2012-10-29T02:04:39Z")
I’m thinking of making a video that explains gravity. Does anyone know where I can get an MP3 of a loud sucking sound? ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [October 29, 2012, 7:50pm UTC](https://boards.straightdope.com/t/crappy-science-instruction/638830/42 "2012-10-29T19:50:36Z")
[Here’s another good demo:](http://www.youtube.com/watch?feature=endscreen&v=YUdR9xESD64&NR=1) 1. cap a plastic bottle, slightly collapsed. 2. twist it up tightly; this compresses the air inside, heating it up via adiabatic compression. 3. Over the course of a few seconds, the warm air loses some heat to the skin of bottle, cooling down a bit. 4. Rapidly untwist the bottle. Adiabatic expansion lets the air cool down again. Because it lost some heat in step 3, it will actually cool down to a temperature below whatever it started at in step 1. If there’s enough humidity in that air (e.g. if you have a small amount of residual liquid water in the bottle), it will condense into fog, a visible manifestation of the lowered temperature. ---
**Author:** ![Hyperelastic](https://avatars.discourse-cdn.com/v4/letter/h/a3d4f5/32.png) [@Hyperelastic](https://boards.straightdope.com/u/Hyperelastic)\ **Post date:** [October 29, 2012, 9:04pm UTC](https://boards.straightdope.com/t/crappy-science-instruction/638830/43 "2012-10-29T21:04:21Z")
> [@Weedy](#): > > This is maybe more of a General Question, but what are the forces acting on the rocket that make it move? The big two would be air drag (if your’re still in the atmosphere) and gravity. ---
**Author:** ![Greg\_Charles](https://avatars.discourse-cdn.com/v4/letter/g/839c29/32.png) [@Greg\_Charles](https://boards.straightdope.com/u/Greg_Charles)\ **Post date:** [October 29, 2012, 9:12pm UTC](https://boards.straightdope.com/t/crappy-science-instruction/638830/44 "2012-10-29T21:12:48Z")
I saw a photo of a lightning bolt that went from the ground to about halfway up to the clouds, and purported to demonstrate that lighting travels from the ground up. No, dipshits, it demonstrates that your shutter was halfway closed as the lighting struck. ---
**Author:** ![Johanna](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johanna/32/8318_2.png) [@Johanna](https://boards.straightdope.com/u/Johanna)\ **Post date:** [October 30, 2012, 5:11am UTC](https://boards.straightdope.com/t/crappy-science-instruction/638830/45 "2012-10-30T05:11:11Z")
Some lightning strokes move from the ground up, and others from cloud to ground. Depends on what instigates them. Don’t listen to me, but listen to [NOAA](http://www.nssl.noaa.gov/primer/lightning/ltg_basics.html): > [@](#): > > Triggered lightning goes from ground to cloud, while “natural” lightning is cloud to ground. > […] > Cloud-to-ground lightning (CG’s) > A channel of negative charge, called a step leader, will zigzag downward in roughly 50-yard segments in a forked pattern. This step leader is invisible to the human eye, and shoots to the ground in less time than it takes to blink. As it nears the ground, the negatively charged step leader is attracted to a channel of positive charge reaching up, a streamer, normally through something tall, such as a tree, house, or telephone pole. When the oppositely-charged leader and streamer connect, a powerful electrical current begins flowing. A return stroke of bright luminosity travels about 60,000 miles per second back towards the cloud. A flash consists of one or perhaps as many as 20 return strokes. We see lightning flicker when the process rapidly repeats itself several times along the same path. The actual diameter of a lightning channel is one-to two inches. ---
**Author:** ![Budget\_Player\_Cadet](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/budget_player_cadet/32/205_2.png) [@Budget\_Player\_Cadet](https://boards.straightdope.com/u/Budget_Player_Cadet)\ **Post date:** [October 30, 2012, 10:27am UTC](https://boards.straightdope.com/t/crappy-science-instruction/638830/46 "2012-10-30T10:27:03Z")
> [@Revtim](#): > > I was just telling my friend, nothing makes me fly into a rage like an improper demonstration of adiabatic expansion. Oh hi, I just thought I’d stop in here and say, as much as I like the OP’s post, Revtim has officially won the thread. 😃 ---
**Author:** ![Weedy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/weedy/32/301_2.png) [@Weedy](https://boards.straightdope.com/u/Weedy)\ **Post date:** [October 30, 2012, 1:23pm UTC](https://boards.straightdope.com/t/crappy-science-instruction/638830/47 "2012-10-30T13:23:11Z")
> [@Hyperelastic](#): > > The big two would be air drag (if your’re still in the atmosphere) and gravity. Yes, they make it stop, but what makes it go? How does a rocket produce thrust, if not via Newtons third law? [Previous page](https://boards.straightdope.com/t/crappy-science-instruction/638830.md?page=2)