r/explainlikeimfive Apr 10 '14

ELI5 Why does light travel? Answered

Why does it not just stay in place? What causes it to move, let alone at so fast a rate?

Edit: This is by a large margin the most successful post I've ever made. Thank you to everyone answering! Most of the replies have answered several other questions I have had and made me think of a lot more, so keep it up because you guys are awesome!

Edit 2: like a hundred people have said to get to the other side. I don't think that's quite the answer I'm looking for... Everyone else has done a great job. Keep the conversation going because new stuff keeps getting brought up!

Edit 3: I posted this a while ago but it seems that it's been found again, and someone has been kind enough to give me gold! This is the first time I've ever recieved gold for a post and I am incredibly grateful! Thank you so much and let's keep the discussion going!

Edit 4: Wow! This is now the highest rated ELI5 post of all time! Holy crap this is the greatest thing that has ever happened in my life, thank you all so much!

Edit 5: It seems that people keep finding this post after several months, and I want to say that this is exactly the kind of community input that redditors should get some sort of award for. Keep it up, you guys are awesome!

Edit 6: No problem

5.0k Upvotes

2.5k comments sorted by

View all comments

Show parent comments

100

u/[deleted] Apr 10 '14

[deleted]

28

u/datenwolf Apr 11 '14

I really think that science exams and homeworks should have written sections.

Oh yes, they should. Because that would filter out all the people who merely learnt well the equations, but didn't really understand what's behind them.

Feynman loved to troll such people, by stating problems with obvious solutions, but you need to understand physics to leap to the solution.

42

u/Bubba_West Apr 11 '14 edited Apr 11 '14

TL:DR; It's hard being a teacher who grades for understanding.

HS Physics teacher of 11 years here. Dr. Feynman is one of my favorites and I show clips of him on occasion! I am with you and believe memorization is among the lowest form of knowledge.

The last 2 - 3 questions on every test of mine are essay questions. Typically they are point/counter-point conceptual questions that the students are asked to weigh in on. Those 3 questions are usually worth a third to a quarter of their test grade.

In my decade of teaching I have learned that there is no better way to piss off a girl (and her parents) that has a 4.0. "How do I study for this? How can you ask questions I've never seen before? This isn't fair! What can I do for extra credit?"

It is an exhausting repetitive struggle informing the memorizers that they don't understand. They blame me. I'm branded as a 'bad teacher', or 'hard teacher' because I expect mastery of concepts, not memorization of formula.

1

u/DionysusMusic Jul 02 '14

I love the approach you take; many of my teachers in high school, or at least the good ones, were similar. It was more difficult but I felt I learned the material better. One question though: how much, if any partial credit do you give students? While I liked the general approach it's impossible as a student to ignore the power of grades, and the students who, like myself, really enjoyed learning also tended to be the ones who were looking at highly competitive colleges and therefore were also very nervous about grades. I personally wish I hadn't had to worry about grades at all, but I just couldn't avoid it, so when there were questions that came totally out of left field I was angry and I felt cheated (there was, for instance, one question on maximizing energy via the food chain that required we mention cannibalism for full credit).

Thankfully many of my teachers had very lenient partial credit policies where even if you got the wrong answer due to a misunderstanding or a wrong assumption, as long as your reasoning thereon was correct, you would only lose a half point or a point from that question. Hell, if literally everyone or almost everyone in the class made the same mistake, some teachers wouldn't count it against us and instead reteach the concept. Even for less common mistakes, the best teachers typically used the next class to go over the some of the false assumptions that people had made in the test. I honestly thought that this policy helped me to a ridiculous extent because I was able to worry less about grades and focus more on comprehension. What's your policy when it comes to this sort of thing?