Electrostatics lab - part 1 of 4 — Transcript

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1. 0:01hey hello and uh
2. 0:03welcome welcome to this uh new and
3. 0:05historical
4. 0:06uh semester of uh uh online
5. 0:10learning and uh it's physics 121
6. 0:13and this is our our first lab and i
7. 0:15thought i would begin by
8. 0:17by taking about 10 minutes here out of
9. 0:19the beginning and saying
10. 0:21all right what and how are we going to
11. 0:23do these
12. 0:24online labs so uh presumably you got my
13. 0:28email last night to kind of explain to
14. 0:30the whole class and
15. 0:32in that email i i said that each monday
16. 0:36and so here we are monday morning
17. 0:38i would go ahead and do a
18. 0:41online lab and uh send it out to you
19. 0:45monday afternoon maybe late afternoon or
20. 0:47maybe in the evening depending on how
21. 0:48long it takes and so
22. 0:49so that's what i'm doing now here and so
23. 0:52this is going to be our first
24. 0:53online lab and so uh like i said we will
25. 0:57do
26. 0:58one lab uh each week uh you've got the
27. 1:01the syllabus
28. 1:02and uh if you've got a chance to look at
29. 1:04the syllabus i hope you did that was
30. 1:05kind of my first instruction step one is
31. 1:07you know go to canvas and read
32. 1:08the syllabus and if you read that you'll
33. 1:11see that we are doing the static
34. 1:12electricity lab
35. 1:13uh this week and so that's what i'm
36. 1:16about to make
37. 1:17for you and so i'm going to describe
38. 1:20these labs
39. 1:22as me and you working as
40. 1:25lab partners you see in a normal setting
41. 1:27in a face-to-face setting here's what we
42. 1:29would do
43. 1:30is you would sit at one of these desks
44. 1:32here in the lab room
45. 1:34and you would have a partner and you and
46. 1:36your partner would go through and read
47. 1:38the lab manual and follow those
48. 1:40in instructions and then you would
49. 1:42answer the questions
50. 1:43you would analyze the data and you would
51. 1:46turn all that
52. 1:47in and so what i'm going to do here
53. 1:49today
54. 1:50is after we get done recording this i'm
55. 1:52going to send out to you
56. 1:54this lab manual okay and so you'll get
57. 1:56this in a pdf form
58. 1:58okay and this this this lab manual then
59. 2:02you will write
60. 2:05and answer the questions now they don't
61. 2:07have to necessarily be in the lab manual
62. 2:09so
63. 2:09you probably don't need to print it
64. 2:13uh you could also type it in but when
65. 2:16you turn it in on
66. 2:17canvas as you'll see it says a pdf
67. 2:20so probably the easiest way to do that
68. 2:22is to use word or google docs and
69. 2:24you know type in the answers if you do
70. 2:26some hand ones then scan it and
71. 2:28send it in in a pdf okay
72. 2:32and as i said in my email last night
73. 2:35uh i've activated canvas uh but i
74. 2:37haven't activated it to the point that
75. 2:39you can turn
76. 2:39anything in and so this first lab
77. 2:42i give i'm gonna give you all week to do
78. 2:44it if this was a normal
79. 2:46uh face-to-face setting uh three-fifths
80. 2:50of you
81. 2:51would do this lab on wednesday another
82. 2:54fifth of you would do it on thursday and
83. 2:56another
84. 2:56fifth of you would do it on on friday
85. 3:00okay and and so in this setting it
86. 3:02doesn't matter when you
87. 3:03you do it it's just due
88. 3:07sunday night and so sometime between
89. 3:10when you get this
90. 3:11monday night and sunday night you go
91. 3:14through
92. 3:15the lap and like i was saying here in a
93. 3:18normal setting you would work with your
94. 3:20partner and that is i would start off
95. 3:22and i would explain the lab and i would
96. 3:25spend here about
97. 3:2620 minutes showing you the equipment and
98. 3:28how to use it and then i would let you
99. 3:30guys start doing it and i would just
100. 3:32kind of walk around the room
101. 3:34obviously with the pandemic we can't do
102. 3:37that
103. 3:37and so the best we've come up with with
104. 3:39doing these online labs
105. 3:41is to do the lab in a way that
106. 3:45partner is me i am
107. 3:49your partner and so kind of pretend
108. 3:53that you're in the lab that you're
109. 3:55sitting at this
110. 3:56table and that we're doing the lab
111. 4:00and so you're looking on and i'm going
112. 4:02to do obviously the the hands-on stuff
113. 4:05i'm going to be the one who grabs the
114. 4:07equipment and
115. 4:08and does it um sadly
116. 4:11that's the part about an online lab is
117. 4:13you're not going to be able to actually
118. 4:15touch this stuff with your hands
119. 4:18but i'm hoping by watching the video and
120. 4:21maybe even
121. 4:22to some advantage of being online i
122. 4:25could expand on
123. 4:27the questions and what we're doing a
124. 4:29little more detail
125. 4:30than maybe you would get on your on your
126. 4:32own so there is
127. 4:34some plus sides to this online lab
128. 4:37and the online lab and particularly
129. 4:38today's lab
130. 4:40is a little more what i'd call a lecture
131. 4:42demonstration lab
132. 4:44in fact today's lab really isn't any
133. 4:46different
134. 4:47than the first lecture and so
135. 4:51i'm assuming you've already seen the
136. 4:54first lecture by the time you get to
137. 4:55this or or maybe not
138. 4:57but maybe i should say you should
139. 4:59because i've gone through
140. 5:01most of these in that lecture
141. 5:04and have kind of explained what's going
142. 5:07on
143. 5:07and the purpose of the lab then is to
144. 5:09give you a kind of a second chance
145. 5:11at learning the physics by you doing it
146. 5:14your yourself
147. 5:16now as you know you actually being in
148. 5:19the lab and doing it yourself
149. 5:21is not possible in this pandemic setting
150. 5:25so that's kind of the bummer part of it
151. 5:28but i think
152. 5:29like i said the good part is is you get
153. 5:30to see the second time and maybe even
154. 5:32get a chance to
155. 5:33uh have me expand on it and there are
156. 5:36some things
157. 5:37done in the in the lab today that i
158. 5:39didn't do in the in the lecture so not
159. 5:41everything is a repeat
160. 5:43but even if it is a repeat
161. 5:46i think that's good because it gives you
162. 5:48a chance to see the second time and as i
163. 5:50wrote in my
164. 5:52email about class just like reading the
165. 5:54book many times
166. 5:56it's good to see the science a couple of
167. 5:58times because
168. 6:00you just really can't comprehend
169. 6:02advanced
170. 6:03science ideas the first time it's not
171. 6:06like i can tell you once and you get it
172. 6:08yeah
173. 6:08you really need to see it a couple of
174. 6:09times and that's why i said and i'll
175. 6:11repeat here
176. 6:12you should read the the textbook then
177. 6:15see the lectures and then re-read the
178. 6:18textbook
179. 6:18and by the time you've done that you've
180. 6:20been exposed to it three times and the
181. 6:21fourth time then
182. 6:22is when you come in here into the lab
183. 6:24and when we come into the lab
184. 6:26we do one of or two of these principles
185. 6:28that we're talking about in class and
186. 6:29that gives you a fourth time to see it
187. 6:32and then ultimately there's a fifth time
188. 6:33where you sit down and do the homework
189. 6:35problems
190. 6:36and and that's how our science class is
191. 6:38designed you get exposure to the same
192. 6:40thing
193. 6:40five times it almost sounds like we're
194. 6:42repeating ourselves but the
195. 6:43reality is you just can't learn it in
196. 6:47your first reading
197. 6:48and you can't learn it in the first
198. 6:50lecture you you've got to do it a couple
199. 6:52of times
200. 6:53and in this case five times before it
201. 6:56truly
202. 6:57sinks in and so that's really the
203. 6:59strategy
204. 7:00of our our advanced science classes now
205. 7:03the
206. 7:04beginning science classes are a little
207. 7:05different you can learn that first or
208. 7:07second reading but but but not this
209. 7:09material so
210. 7:10we're giving you five opportunities here
211. 7:12to really
212. 7:14uh digest this so with that all said
213. 7:19again think of me as your lab partner
214. 7:23okay and this is the equipment here for
215. 7:26today
216. 7:27and so i'm gonna work with that and i
217. 7:30want you
218. 7:31if you haven't already to open up that
219. 7:34pdf that comes in the email with this
220. 7:36link
221. 7:37and it'll have the lab manual and go to
222. 7:39page one
223. 7:40because page one is these 25
224. 7:44steps these 25 observations
225. 7:47that you are asked to do and at the
226. 7:50end of these 25 and so that's the part
227. 7:53we will do together
228. 7:55we will do these 25 and then at the
229. 7:58end there is going to be some
230. 8:01discussion questions and that'll be true
231. 8:04on all the labs and and
232. 8:06that's the part that i won't do with you
233. 8:08that's the part that i'll stop
234. 8:10and let you answer them and you have a
235. 8:14couple of ways you
236. 8:15uh you could work with other students if
237. 8:17you prefer to kind of go through those
238. 8:19discussion questions
239. 8:21or you can work on them on your own
240. 8:24and just kind of of answer them
241. 8:28uh but this like i said is the part that
242. 8:31that that that i will leave for you
243. 8:34to kind of answer and so we'll do what i
244. 8:37like to call the raw data
245. 8:38we'll actually then the stuff that we
246. 8:41need the equipment for the stuff that we
247. 8:43need to be in the lab for that's the
248. 8:45part we will do together
249. 8:47the other parts like calculations and
250. 8:50graphs
251. 8:51and answering questions and drawing
252. 8:54conclusions
253. 8:55whatever the lab is that's the stuff
254. 8:57i'll leave for for you to do where you
255. 8:59can then
256. 9:02hopefully answer those by seeing what
257. 9:05i've done here with you but
258. 9:06if you can't of course that's your
259. 9:08chance to you know ask
260. 9:10some questions here and so as i said in
261. 9:13my my email
262. 9:14i'm going to try to give you all the
263. 9:16material for one week and let you kind
264. 9:18of just kind of work through that
265. 9:19during the week and shoot off questions
266. 9:21as you have questions and i'll answer
267. 9:23them
268. 9:24but that's why then i i want to then
269. 9:26kind of put a big block on friday
270. 9:28and just say all right now
271. 9:32i'll turn on the zoom meeting and say
272. 9:35all right i'll
273. 9:36be here for five hours and i
274. 9:40you know pop in so i can see your face
275. 9:42if you if you want or leave your camera
276. 9:44off doesn't really uh matter
277. 9:46i've got some learning how to do zoom
278. 9:48myself so between now and friday i gotta
279. 9:51figure out how i can do a couple things
280. 9:53on on zoom so hopefully the first
281. 9:55session will go somewhat smoothly
282. 9:57but that's the design here is that all
283. 10:00this stuff you're learning here which is
284. 10:02really chapter 23 in the survey book or
285. 10:04it's chapter five in the
286. 10:06second volume of the open stacks book
287. 10:09this is on
288. 10:09the electric field and just kind of that
289. 10:12concept of what's going
290. 10:13on all right well maybe now is time to
291. 10:17actually start
292. 10:18the lab okay i think you you got this
293. 10:21gist and so that's what i'm getting at
294. 10:23is just always think of these
295. 10:24these online labs as me and you are
296. 10:26partners okay
297. 10:27everybody has a partner and i'm
298. 10:29everybody's partner okay
299. 10:30and so you can just open it up so
300. 10:33hopefully by this time
301. 10:34you know on your computer screen or
302. 10:36maybe uh you printed it out
303. 10:38you're looking here at page one and
304. 10:41page one starts off by saying
305. 10:45you should know these four facts okay
306. 10:48and so these these four facts come
307. 10:52from uh the lecture and so let me begin
308. 10:55by by just
309. 10:57pointing out the obvious here fact
310. 10:59number one
311. 11:00it says here all matter consists of
312. 11:02electrically charged particles
313. 11:04now let me take this opportunity to draw
314. 11:06something here on on the board
315. 11:07if you didn't quite get this out of the
316. 11:10uh lecture
317. 11:11if you took any material
318. 11:14and i'll just pick one material that
319. 11:16we're going to be working with here
320. 11:17today here here's a a piece of vinyl
321. 11:20and so we're going to be working with
322. 11:21this piece of vinyl but it doesn't
323. 11:22matter what the material is a piece of
324. 11:24aluminum a piece of vinyl a piece of
325. 11:26lead
326. 11:27the idea here is that it would be made
327. 11:31out of
328. 11:32atoms and every atom has
329. 11:36a center part a nucleus and in that
330. 11:38nucleus has these protons and so they
331. 11:40are positively charged
332. 11:41and that's going to be our focus the
333. 11:44charges
334. 11:45on the outside are the electrons and so
335. 11:48when this says
336. 11:49all matter consists of electrically
337. 11:52charged particles this is what they're
338. 11:53trying to say they're trying to say
339. 11:54everything's made out of atoms and the
340. 11:55atoms are made
341. 11:56out of protons and electrons there's
342. 11:58neutrons in there too but as far as
343. 11:59electricity is concerned that that's not
344. 12:01a uh
345. 12:03relevant discussion for us uh we're only
346. 12:05interested in things that have charges
347. 12:07and so the protons and
348. 12:08the electrons now look at number number
349. 12:12two
350. 12:12this is an important concept if you
351. 12:14didn't get it out of the lecture
352. 12:15the negative charged units that is the
353. 12:18electrons are the ones that are mobile
354. 12:20so if i were to maybe draw a second atom
355. 12:23here in this picture
356. 12:25uh maybe even a third one
357. 12:30and i were to play with this material by
358. 12:32maybe bringing another material to it
359. 12:35or maybe just in the material itself
360. 12:39the things that move around the things
361. 12:42that can break off from an
362. 12:44atom and go to another atom are the
363. 12:46electrons
364. 12:47and the electrons have this negative
365. 12:49charge by our definition thank you to
366. 12:51benjamin franklin
367. 12:53and and and so the things that moves are
368. 12:55the negatives so keep that in mind
369. 12:57we are never you're never going to hear
370. 12:59me saying hopefully you will never say
371. 13:01it
372. 13:01that oh it's positive because the
373. 13:04positives moved over blah blah blah no
374. 13:05no no
375. 13:06the positives do not move
376. 13:10at least in a solid i should emphasize
377. 13:11that in a solid because in a solid
378. 13:14the positives are the atoms themselves
379. 13:16they're they're locked into place and so
380. 13:18keep that in mind as we move along
381. 13:21that the uh the electrons are the stuff
382. 13:24that are
383. 13:25are mobile the stuff on the the the
384. 13:27outside number three
385. 13:30equal numbers of positives and negatives
386. 13:33make something
387. 13:34neutral sometimes we like to say when we
388. 13:37hold up a piece of vinyl we like say oh
389. 13:38this has no charge
390. 13:41that's misleading we should really say
391. 13:43this is neutral
392. 13:45and what we mean by that it is it has no
393. 13:47net
394. 13:48charge that is there is an equal number
395. 13:51of positives and negatives
396. 13:53because hopefully what you learned in
397. 13:54the lecture and what you'll see here in
398. 13:56the lab
399. 13:57is there is a lot of interaction going
400. 14:00on between positives and negatives or
401. 14:02two positives or two negatives
402. 14:05and so it's important to realize
403. 14:08that even though something has
404. 14:12no net charge that is it's neutral
405. 14:15it still has a lot of charges and you'll
406. 14:17see that in these 25 steps we go through
407. 14:20that we will talk about that important
408. 14:23distinction
409. 14:24when something is neutral it's neutral
410. 14:27it's it's not that it doesn't have any
411. 14:29charge it's just
412. 14:30neutral all right and
413. 14:33the fourth and final thing is about
414. 14:37conductors and in particularly this says
415. 14:39air is not a conductor
416. 14:41now that word conductor and hopefully
417. 14:43this is what you got out of the lecture
418. 14:44but it's a good repeat here
419. 14:45means that the charges and remember the
420. 14:48ones that are mobile are the electrons
421. 14:49and so the electrons can move around
422. 14:52so maybe coming back here to my picture
423. 14:55if the electron can freely move
424. 14:58from one atom to another until it can
425. 15:00move anywhere in that material
426. 15:03we call that a conductor
427. 15:06but if it can't move that that is this
428. 15:09if i were to take
429. 15:10this one away
430. 15:14it would be missing a negative
431. 15:17and if it was what we call an insulator
432. 15:20or a non-conductor
433. 15:22then that missing charge would actually
434. 15:24stay in that same physical location
435. 15:27whereas if it was a conductor something
436. 15:29like this might happen
437. 15:32maybe the electron from the atom over
438. 15:35here moves over and so even though we
439. 15:38took the electron away from this atom
440. 15:42it is now missing it right here
441. 15:46and one of the things that we will learn
442. 15:49and i don't think it was covered in the
443. 15:50first lecture so you may not have gotten
444. 15:52this far
445. 15:53quite yet is that
446. 15:56then the electrons
447. 16:02if you take them out of the middle of a
448. 16:03conductor
449. 16:05things flow around and the ones that are
450. 16:08missing
451. 16:09are at the surface of that conductor in
452. 16:12fact i'm quite sure that that's chapter
453. 16:1425 or
454. 16:15chapter six in the openstax book so
455. 16:20no ch it's it's gauss's law so i'm quite
456. 16:23sure you haven't seen that that's that's
457. 16:24next week's material so
458. 16:26forgive me i guess i'm getting ahead of
459. 16:27myself here but i am trying to point out
460. 16:30that there is an important difference
461. 16:33between
462. 16:34a conductor and an insulator
463. 16:37and you're going to see that in the
464. 16:38experiment today you're going to
465. 16:41then see the behavior and so you will
466. 16:43see as we go along
467. 16:45for the rest of this semester
468. 16:48that we will always ask ourselves are we
469. 16:51dealing with a conductor or are we
470. 16:53dealing with an insulator
471. 16:55because the behavior is very different
472. 16:57can they move or
473. 16:58can they not move and that's that's
474. 17:01that's crucial
475. 17:02so with that in mind let's start these
476. 17:0525 steps and
477. 17:06and here's what i want you to do i want
478. 17:08you to get out a piece of paper or you
479. 17:10can do it on a computer screen whatever
480. 17:13and let's just run the 25 steps the 25
481. 17:17experiments make the observations and
482. 17:19just just write down an answer
483. 17:21and that'll be half of the of the lab
484. 17:24and i said earlier the other half of the
485. 17:26lab then
486. 17:28will be you then answering these
487. 17:31six uh questions all right
488. 17:34so i think finally we're ready to begin
489. 17:38i hope i didn't take
490. 17:39too much time here at the beginning but
491. 17:40i did want to kind of set the stage for
492. 17:42how we're going to do these labs in a
493. 17:45remote setting
494. 17:46and i also you know wanted to just
495. 17:50take it extra slow to make sure you you
496. 17:52know those
497. 17:53four facts those those four facts are
498. 17:56are real important you're going to see
499. 17:57as we
500. 17:58keep coming down to it all right so here
501. 18:00we go
502. 18:01step number one experiment number one
503. 18:03and let's see what happens it says here
504. 18:05suspend a pith ball or an aluminized
505. 18:09plastic ball okay so i'll stop right
506. 18:10there
507. 18:11we already have that done for you right
508. 18:12here here's a piece of wood here's this
509. 18:14aluminum
510. 18:15ball the outside is painted with a small
511. 18:18amount of aluminum paint what i want to
512. 18:21emphasize with this
513. 18:22is since you can't really touch it
514. 18:24yourself is that
515. 18:26this outside coating is a conductor it's
516. 18:29made out of
517. 18:30aluminum and it's
518. 18:33very very light and as you'll see we
519. 18:35want to see if it responds
520. 18:37to any forces that's why we want it to
521. 18:39be light but we also want it to be a
522. 18:40conductor
523. 18:41and so note that we have a conductor a
524. 18:43very light conductor
525. 18:45hanging from a string so that's what
526. 18:46this forms one i'll read it again
527. 18:48suspend a pit ball in an aluminized
528. 18:50plastic ball by a thread
529. 18:52and touch the ball with your fingers
530. 18:56to quote unquote ground it
531. 19:00the ball will start off as neutral why
532. 19:03is this all right so we don't really
533. 19:04have an experiment to do other than
534. 19:06to make sure this ball is neutral and so
535. 19:10as we begin our step two we need to know
536. 19:13that that ball is neutral
537. 19:15but they're beginning to ask why and so
538. 19:18maybe that is best answered with a
539. 19:20a picture let me kind of get rid of this
540. 19:23picture
541. 19:24here but if i were to take
542. 19:28that aluminized ball right there and so
543. 19:31that'll be my
544. 19:32my ball there and let's just say there
545. 19:35were some
546. 19:36extra electrons on it so i'll put a
547. 19:38little minus here and a minus here and a
548. 19:40minus here and a minus here
549. 19:42and a minus here now remember
550. 19:45this is made out of aluminum and
551. 19:47aluminum has
552. 19:49atomic number 13. so there are 13
553. 19:53protons
554. 19:54in the nucleus i won't bother to write
555. 19:56out the 13
556. 19:57and then there are 13 electrons and i
557. 20:00won't bother to draw
558. 20:0113 electrons either but if it's neutral
559. 20:05that would be an exact match and you
560. 20:07wouldn't have these extras on the
561. 20:09outside
562. 20:10what they're trying to get at here is
563. 20:14a property that hopefully you saw in the
564. 20:16in the lecture that we're also going to
565. 20:18see here
566. 20:19that like charges repel each other
567. 20:23so if you add some extra electrons on
568. 20:25here and i
569. 20:26probably could have drawn it a little
570. 20:29little better they will push away from
571. 20:32each other
572. 20:34and in this case they repel
573. 20:37one another and so they'll spread out as
574. 20:40far as they can get so that's part of
575. 20:42the reason they get on the surface
576. 20:44and they'll kind of evenly space
577. 20:45themselves at least if it's a sphere
578. 20:48so that they're the same distance apart
579. 20:53and of course they can move around
580. 20:55because it's conductor
581. 20:56that's important here okay now watch
582. 21:00what would happen
583. 21:01if i came along with my finger and so
584. 21:04here is my finger
585. 21:08uh what does a finger look like a little
586. 21:12fingernail
587. 21:14a couple joints all right that's the
588. 21:17best i can do
589. 21:18but but but here's my my finger and my
590. 21:20finger comes along and
591. 21:21touches that pith ball
592. 21:25you need to understand that the human
593. 21:27body is a
594. 21:28semi semi-good conductor itself
595. 21:32so what would happen
596. 21:35well these negatives then have a chance
597. 21:39to go
598. 21:41somewhere further and so what will
599. 21:43happen
600. 21:44is this one because again it's being
601. 21:46repelled from that one and that one of
602. 21:47course it
603. 21:48settled in the middle because they were
604. 21:49kind of fighting each other but now it
605. 21:50goes hey i'm going to go over to here
606. 21:54and if my body's a conductor it'll go
607. 21:56not just on my finger it'll go down my
608. 21:58arm and maybe go all the way down to my
609. 22:00toe it's trying to get as far away
610. 22:02excuse me it's trying to get as far away
611. 22:04from these other ones as possible
612. 22:07well then of course now the second one
613. 22:08is going to go well wait a minute
614. 22:10i'm still being pushed by that one now
615. 22:12granted that one's gone but this one's
616. 22:14still pushing me away
617. 22:15this one's way over on the on the toes
618. 22:18somewhere over here
619. 22:19so then the second one goes and then the
620. 22:21third one goes
621. 22:25and here's the real key if the object
622. 22:28that is touching it which is me is much
623. 22:31much
624. 22:31bigger than this little pitfall so that
625. 22:35was the key i'm big it's small
626. 22:38it can get all these electrons can get
627. 22:40far away from one another
628. 22:42when they're on the big object compared
629. 22:44to the small object
630. 22:46and so as a result these guys
631. 22:49push each other away and they end up
632. 22:52pushing them on the
633. 22:53biggest object and so
634. 22:56this is why we want to touch it we want
635. 22:59to
636. 23:00neutralize it i know
637. 23:03because the light charges repel each
638. 23:05other then when i take
639. 23:06a pit ball like this a conductor like
640. 23:09that and it's small
641. 23:11and i touch it with something big which
642. 23:12is me
643. 23:14then they leave my my small
644. 23:17object and go onto the big object now i
645. 23:20suppose you may argue
646. 23:23maybe not the last electron okay
647. 23:26so these electrons remember are pretty
648. 23:28pretty small and we're talking about
649. 23:30billions and billions of billion when
650. 23:31you say you have some extra electron
651. 23:33it's not like i have an extra five like
652. 23:34i drew on here or six is what i drew on
653. 23:36here
654. 23:38we're talking billions and billions
655. 23:42so if one stays on there i i'm gonna
656. 23:44call it neutral nonetheless
657. 23:46okay so maybe there's one electron still
658. 23:49on it
659. 23:50but most of them went on to me in fact
660. 23:51by extension of that
661. 23:53how would i get the electrons off of me
662. 23:58yeah and i hope you're guessing that
663. 24:00yeah touch something bigger than me
664. 24:02preferably a lot bigger than me if it's
665. 24:04only the same size as me
666. 24:06probably half of them go off and the
667. 24:07other half remain on me but what is the
668. 24:09biggest
669. 24:10object around
670. 24:14yeah the earth the ground so
671. 24:17when we like to neutralize our
672. 24:19electronics we call it grounding
673. 24:21because the best way to make it neutral
674. 24:23is to touch the biggest object and the
675. 24:25biggest object is the ground
676. 24:27for me that's pretty easy watch i'll
677. 24:28just come over here and i have a sink
678. 24:31and if i just grab this piece of metal
679. 24:33this pipe right here
680. 24:35this piece of pipe is a conductor and it
681. 24:37goes down and it's buried into the
682. 24:39ground and so now i am essentially
683. 24:41touching
684. 24:42mother earth and these electrons have
685. 24:44now left
686. 24:45me and so i'm neutral now
687. 24:49of course i don't think that was real
688. 24:51relevant that that i be neutral
689. 24:53but i wanted you to understand that word
690. 24:55ground it and and of course your author
691. 24:57put it in
692. 24:58quotes because
693. 25:01you're not really touching the ground
694. 25:04you're touching it with a
695. 25:05a bigger object and so
696. 25:09that's what those third plugs are for
697. 25:11maybe i'll
698. 25:12i'll grab a little device here you know
699. 25:15the
700. 25:15this right here this this is what we
701. 25:17call the the grounding wire
702. 25:20because when i plug in this apparatus
703. 25:25there's a little wire that runs through
704. 25:27our walls
705. 25:29and literally that that that wire goes
706. 25:31out the side of our building
707. 25:33and if you go over to the side of our
708. 25:34building that wire is then
709. 25:36tied and clamped onto a copper rod
710. 25:40that copper rod is then pounded into the
711. 25:42ground 20 feet
712. 25:44and so this right here is touching the
713. 25:47ground
714. 25:47which is why it becomes a safety device
715. 25:49and so you know so no one hurts
716. 25:50themselves what we do is then we
717. 25:52we take this metal plate and we we tie
718. 25:55it to this wire which is then connected
719. 25:56to the ground
720. 25:57and so there is no way that this metal
721. 25:59plate can ever develop
722. 26:01a charge on it because if it started to
723. 26:04it would flow off and go to the biggest
724. 26:05thing which would be the ground
725. 26:06and so that way we will never
726. 26:08electrocute
727. 26:10ourselves that that's the idea there
728. 26:12well i digress and i hopefully didn't
729. 26:14use too much time there but
730. 26:15uh that first one is grounded
731. 26:19and so hopefully and if you want to
732. 26:21pause the video this might be a good
733. 26:23time you can answer
734. 26:24that question why is this true
735. 26:27and you could keep it simple you don't
736. 26:28have to go into long dialogue like i
737. 26:30just did just say
738. 26:31you know because like charges repel
739. 26:34each other they will push off to the
740. 26:36biggest object
741. 26:38and therefore the small object will now
742. 26:40be
743. 26:41neutral maybe maybe that's a good line
744. 26:43i'm not worried so much about your words
745. 26:45i'm just hopefully communicating with
746. 26:47you that you're seeing this big picture
747. 26:49why would touching it neutralize it
748. 26:52and i should emphasize it's not just
749. 26:55touching it but it needs to be a
750. 26:56conductor and it also needs to be a
751. 26:58small object
752. 26:59but if we meet all those conditions
753. 27:00which we do then this is neutral
754. 27:02all right so here's what i need to know
755. 27:05here
756. 27:05so let me erase this this picture here
757. 27:07for just a second
758. 27:09and let me come back up here and
759. 27:12draw then the pith ball and say okay now
760. 27:15i'm ready for
761. 27:15step two and i have a neutral pitfall
762. 27:18and i want to emphasize that that was
763. 27:20one of our four facts at the beginning
764. 27:22when i draw this pit ball i won't put
765. 27:24any pluses or minuses in here
766. 27:25because i my drawings when i do pluses
767. 27:27and minuses those are the net charges
768. 27:29those are the ones that are above or
769. 27:31below
770. 27:32uh the
771. 27:36i'll call it the par if you will when
772. 27:39the two when the two balance each other
773. 27:41and so right now i have
774. 27:43zero net charge i've got a lot of
775. 27:45positives and a lot of negatives
776. 27:47because here's what's kind of fun so
777. 27:51experiment number two says take a piece
778. 27:53of acetate so here's my acetate
779. 27:56and a piece of wool
780. 27:59bring the acetate near i'm sorry
781. 28:02rub them together and then bring it near
782. 28:04all right so i'm going to start here by
783. 28:06rubbing now let me just pause
784. 28:11here i think is the advantage of the
785. 28:14online labs
786. 28:15is i could say a little bit more than if
787. 28:17you were just sitting there and rubbing
788. 28:18it yourself so if you didn't catch this
789. 28:20out of the lecture let me try to explain
790. 28:23it now
791. 28:23but when you bring two materials
792. 28:25together and you rub them like this
793. 28:27okay and so
794. 28:30uh maybe i'll take one material and
795. 28:34another
796. 28:34material and i'll just make two
797. 28:36rectangles here
798. 28:37but when you rub them and so in this
799. 28:39case wool and acetate
800. 28:43what touch each other are the stuff on
801. 28:46the outside which are the electrons
802. 28:49and so if you imagine an atom here and
803. 28:51an atom here and an atom here
804. 28:53and on this material and atom what's
805. 28:56actually coming into contact
806. 28:58are the electrons and so when you rub
807. 28:59them
808. 29:01you could actually end up scraping
809. 29:03electrons and
810. 29:04and and you could scrape them off of
811. 29:07both materials
812. 29:09it's kind of like if kind of in a weird
813. 29:10imaginary way if you think of king kong
814. 29:13and and king kong picks up two cars
815. 29:16and he puts them together and rubs
816. 29:19it's the bumpers that touch and it's the
817. 29:22bumpers that rub off
818. 29:23when he puts them together and rubs and
819. 29:25so these bumpers come flying off
820. 29:27and that's what's happening on a
821. 29:28microscopic scale
822. 29:31now they get attracted
823. 29:34back and if these are different
824. 29:38materials
825. 29:43the way the positives are distributed in
826. 29:46them
827. 29:46are a little different in the acetate
828. 29:50versus the wool and without getting into
829. 29:53the details of how they are distributed
830. 29:55which
831. 29:56would be a fun topic in material science
832. 29:58and that's not exactly where we want to
833. 29:59go here today
834. 30:01but they will attract the electrons back
835. 30:05and one will be stronger than the other
836. 30:07and so what will end up happening
837. 30:09is the electrons will go more
838. 30:12towards one than the other again it's
839. 30:14like king kong and the cars and the
840. 30:16bumpers
841. 30:17and you rub them and if one car
842. 30:20is say more magnetic than the other and
843. 30:23of course we're talking about
844. 30:24electricity
845. 30:25magnetism so i hope you know i don't
846. 30:26lose you in my analogy here
847. 30:29but if one car was magnetic and another
848. 30:31one is not when you
849. 30:32when you knock off the two bumpers those
850. 30:34two bumpers will go to the car that has
851. 30:36the magnet
852. 30:37and so that one will have extra
853. 30:39electrons and the other one will be
854. 30:40missing some electrons
855. 30:42and so what's going to end up happening
856. 30:43is let's just say the electrons go this
857. 30:45way
858. 30:46then i'm going to say that this material
859. 30:48becomes negative and this
860. 30:50material lacking the negatives is now
861. 30:53positives
862. 30:54so remember it's the negatives that move
863. 30:56and so one of these materials becomes
864. 30:58positive and one of them becomes
865. 30:59negative
866. 31:01and so i am rubbing this and at this
867. 31:04point they don't say
868. 31:05which one it is although i did say it in
869. 31:07the lecture so hopefully you know which
870. 31:09which one it is but i'll
871. 31:10i'll leave that for step seven as we try
872. 31:12to discover which one it is or they
873. 31:14i think they tell us somewhere about
874. 31:15step seven or maybe it's a little later
875. 31:17uh
876. 31:1813 well it's coming up i know that all
877. 31:21right
878. 31:22but anyways here i am i am rubbing it
879. 31:28and you know what maybe that's the
880. 31:30advantage of the online lab
881. 31:32i'm going to tell you what it is so
882. 31:34there's no curiosity i'm going to get a
883. 31:36little bit
884. 31:36a little bit ahead of the game if you
885. 31:38will but i know
886. 31:40and you'll you'll see this being proved
887. 31:41later on and when i rub this
888. 31:43the electrons are going to the wall and
889. 31:46so the acetate is now
890. 31:48lacking electrons which means it's it's
891. 31:50positive
892. 31:51okay so here's my acetate
893. 31:56okay so what they want you to do in this
894. 31:59one
895. 32:00is really just an observation bring it
896. 32:03near the pit ball and see if anything
897. 32:04happens now remember the pitfalls
898. 32:06neutral
899. 32:07[Music]
900. 32:11but they also say don't let it touch so
901. 32:14i'll do it again
902. 32:15and i hope you noticed
903. 32:18that there is an attraction it's not a
904. 32:21very strong one
905. 32:22but there is a small amount of
906. 32:25attraction
907. 32:26and that's what you should just write
908. 32:27down and so again if you're in front of
909. 32:29your computer screen here and
910. 32:31you're answering your first online lab
911. 32:33question number two just say
912. 32:35attraction maybe best if you put small
913. 32:37attraction because we're going to see a
914. 32:38lot
915. 32:39stronger attractions real soon but they
916. 32:41say don't let it touch
917. 32:42so i'm not gonna
918. 32:46you know let it get too close there
919. 32:50okay so keep in mind we'll talk about
920. 32:52this later that the pitball was neutral
921. 32:54and this was positive all right more on
922. 32:57that to come but let's go to step three
923. 32:59now step three says try this a little
924. 33:01different it says
925. 33:02charge the vinyl strip all right so i'm
926. 33:04gonna grab the other material
927. 33:06the other material is vinyl i'm gonna
928. 33:08rub it
929. 33:10it says rub with the wool and bring the
930. 33:12charged vinyl strip
931. 33:14near the neutral
932. 33:17pit ball so it's again still should be
933. 33:19neutral i haven't you know put any
934. 33:21charges on it there's no way any charges
935. 33:23could get on remember the
936. 33:24air this was that point number four here
937. 33:26the air is a conductor there's
938. 33:27there's no way the electrons could come
939. 33:29on and off after i touched it when i
940. 33:31touched it i neutralized it that was
941. 33:32back in step one all right now i'm gonna
942. 33:36just say the same thing happens here
943. 33:37with the vinyl that when i rub them i'm
944. 33:40going to free
945. 33:41electrons they're going to be attracted
946. 33:44back
947. 33:45to one material a little bit more than
948. 33:47the other
949. 33:49we pick vinyl because vinyl really loves
950. 33:51electrons that's good and bad you're
951. 33:53going to see
952. 33:53parts of these labs are going to be hard
953. 33:54to show you things that happen because
954. 33:57this thing sucks up electrons so well
955. 33:59but on the other things
956. 34:00this is nice because it sucks electrons
957. 34:02so well
958. 34:04so with that in mind as i do this
959. 34:07and i'm freeing up electrons when i rub
960. 34:09it and then they
961. 34:10get attracted back they mostly go to the
962. 34:15to the vinyl okay so
963. 34:21vinyl now is negative keep that in mind
964. 34:26the pitball is neutral keep that in mind
965. 34:29bring it close see what happens
966. 34:36don't let it touch okay maybe i'll do it
967. 34:39a second time
968. 34:40but i'm hoping you see that it too
969. 34:43attracted
970. 34:46there it is yep definitely definitely
971. 34:51attractive and we'll come back and talk
972. 34:54about this a lot more
973. 34:56but remember the acetate was positive
974. 34:59and it attracted a neutral that was step
975. 35:00two
976. 35:02but now the vinyl that is now
977. 35:05negative it has more negatives than
978. 35:07positive so we call it negative
979. 35:09it too attracted the neutral
980. 35:13and that's kind of interesting but
981. 35:16let's keep going here all right and so
982. 35:18oh
983. 35:19by the way i should say so write down on
984. 35:21step three that it is attractive
985. 35:23and you can even say a small amount of
986. 35:25attraction because really that is
987. 35:27kind of small you'll see a lot more
988. 35:28coming up here all right so let's go to
989. 35:30step four
990. 35:31step four says now charge the vinyl
991. 35:34strip
992. 35:35okay here it is
993. 35:38um by rubbing it with wool and
994. 35:42touch this time this time we're going to
995. 35:43actually touch touch the vinyl strip to
996. 35:46the pit ball
997. 35:48okay and then see what happens
998. 35:51all right so i'm going to bring it close
999. 35:54and touch it now
1000. 35:58here's kind of the good and bad of our
1001. 36:01vinyl
1002. 36:04i'm going to touch it a couple of times
1003. 36:10ah finally
1004. 36:14i'm getting to what you should be seeing
1005. 36:17and i hope you see that when i let it
1006. 36:20touch this time
1007. 36:22something different happens it's
1008. 36:26it's repelling
1009. 36:29and so at this point why don't you just
1010. 36:31write down what you observe because
1011. 36:32that's what step four is they're not
1012. 36:33trying to get you to explain it quite
1013. 36:35yet so
1014. 36:35i'll hold off on explaining it but
1015. 36:37that's coming up here so what happens it
1016. 36:39it
1017. 36:40it repels now
1018. 36:43step five says bring the acetate all
1019. 36:46right
1020. 36:48so now just just to remember when i rub
1021. 36:50the acetate the f stays positive
1022. 36:52let me bring it near the pit ball
1023. 36:55and you will see
1024. 36:58that there's attraction and i'm hoping
1025. 37:00you see there's a little more attraction
1026. 37:02than there was before when we did this
1027. 37:05back in step two
1028. 37:08and we'll talk about the physics of it
1029. 37:10coming up here
1030. 37:12but the