I thought today's lecture on cosmology was great. I wrote my paper on the physics of a curveball, and I was wondering if you could explain to me what the wake deflection force is. I am aware of the Magnus Force, and I based my paper around that. Bloomfield however, in his book, says that the wake deflection force is equally as important as the Magnus Force. His explanation of it was totally confusing though!

glad to hear cosmo went well... as for wake deflection force. The short version is that behind all moving object in a fluid is a "wake" (yes the same thing from speed boats). This is turbulent air that gets bunched up behind the ball in your case. This wake is not necessarily symmetric behind the ball--- that is if the ball is being pushed left (curving) the wake may be built up behind and to the right of the ball..That is, the wake is deflected from being symmetrically behind the ball to be shifted to one side or the other. This does two things: it creates high pressure on one side versus another (pushing the ball left) and it encourages air flow faster to the other side (where it is free to flow unimpeded by the wake). This faster air flow means lower relative pressure. Does this make sense? Cool, eh? It's physics.

If the universe bends over, does that explain worm holes (think thats what its called) and how it takes one to another part of the universe?

Well... we don't exactly know about wormholes yet basic connections between black holes (and their counterparts mathematically). But the basic idea is that the gravity is SOOOOOO strong that it warps space so that it no longer linear --- the shortest object between two points is no longer a straight line for instance. In this case you can connect different parts of space (theoretically).

Several weeks ago we where dicussing things on the sub-atomic scale. Now we are discussing things on the astronomic scale. Can you give us a size comparision between the two? What is the size of an atom (or nucleus) in meters? What does this comapare to in cosmology? How long would it take for light to reach the nucleus of an atom?

excellent questions. It is worth visiting the powers of 10 site linked on our "useful simulations" links... it gives a bit of a scale. Atoms are mesured in Angstroms ... 10^-10m. If light travels 10^8 meters/ second than to travel 10^-10m would take 10^-18seconds --- 0.000000000000000001 seconds.

The cosmology stuff was very interesting to learn however i kinda didnt like how it wasnt related to anything else that we did.

well... yes and no.. indeed partly a survey. Though we did use many of the same things we learned before... how light is emitted, the doppler effect for sound, and in fact the mechanism behind stars is the same as for nuclear weapons. So in many ways... same stuff different application.

Just as a random comment, I think it'd be funny if you somehow related a cosmology question to Star Wars on the final. hahaI've decided handing out candy is the best way to encourage class participation. It gives you that extra incentive to participate whereas you might not have otherwise. Although it is rather unprofessional and not traditional, it certainly works.

heyyyyyyy I"M a professional... that's why I'm PROFESSOR Finkelstein ; )

I really wish you had better explained the red shifting in class on Thursday. For some reason I didn't quite pick up the ideas behind the math equations. Could you explain this?

sure... this is just the doppler effect (where I bashed the speaker into my head ... sigh). As a moving source is coming towards you you hear a higher pitch (the train sounds higher in frequency when it is coming towards you). When it leaves it is lower frequency. The faster the train is moving the more the sound is shifted. The same thing happens with light. When something is moving towards you it is higher frequency (bluer) and away from you is lower frequency (redder). We know what lines a hydrogen atom is supposed to emit (you did this in lab); however if the hydrogen lamp were moving away from you, the colors would be shifted just a little bit...every one of those lines would appear a little more red than it did in lab. By meausring the difference in frequency of these lines, you can tell how fast it was moving and in what direction.

I just loved doing the presentations in labs. It was a shame that people were limited by time and couldn't give more in-depth presentations. Perhaps you could try meeting 2 more weeksfor labs so people would have more time to present? It just seemed ashame for people to have obviously put so much work into their research and not be able to do it justice by sharing it with others.Thanks again!

great idea. I was mighty impressed with the work ya'll did.

Since this is probably the last extra credit, I wanted to say what I found was one of the best ways for me to learn. I think having to write out essays and justify my answers made me really think about the questions and the principles behind them. I'm usually a person who gets a formula and then just punches in the variables to get an answer, but this class forced me to truly understand the material. While the writing was kind of a pain and time consuming, it helped me learn much more information than otherwise, so thanks for making me suffer.

Right -on .. thanks for the feedback. It is helpful for everyone to know... and I think you're onto an important mechansims for learning.... we really understand things when we have to explain them.

I'm really glad that you are holding a review session next week because our final is on Sat. and we don't have a lot of time to study. Thanks.

Let me know how it is going please...

I found the classes on the cosmos to be very well done. You covered a lot of material and presented it well. For concepts I didn't quite get, the pictures and drawings in the notes helped solidify everything. Thanks.

glad to hear -- and a major shout out to Ward.

one question - where is the universe expanding into? As air gets hotter within a balloon the balloon expands within the space of the room. Into what space, do physicists think, is the universe expanding into?

great question. It is just expanding. Not into anything. What if every dimension that we know of is the universe but they are just getting bigger??

Also, I have one more very serious physics question that has been nagging me. I think about it a lot and I just can't figure out it out. I was hoping you could help me find the solution... The question is this... What is Einstein smoking in all those pictures???

(part of the secret physics pact, I can't tell you... yet).

I found the information over the past two days very interesting. I registered for cosmology next semester and I got really excited for that class. I hope that it talks about all of these crazy and wacky things to think about (like size and what does the universe expand into). I really like learning about things that make me think and question what is out there beyond me because I am willing to admit that I am not the center of the universe. I wanted to give Ward some feedback too. I think he did a great job with the slides and introducing all of these cool ideas like dark matter and energy. I think he went a little too fast through cosmic background radiation, especially since it was two questions on the homework. I thought some more detailed explanation of that would have been great because I didn't really understand it. Lastly, I just wanted to say thanks to you and your learning assistants for the help sessions because I think my success in understanding in this class can be attributed a great deal to that help.

Thanks for the excellent and constructive feedback.

Is our name attached to these comments?

yes, but I don't look at them.... that is I download them anonymously.

I really enjoyed learning the two last sections, exponential growth and cosmology!

good to hear.

Unfortunatley I was unable to attend two classes ... yet I still went online to review the slides of what went on in class. The slides definitely helped me to understand what we had covered in class. Unfortunately, it doesn't seem like the slides are detailed enough to do homework off of. I know that attending lectures are very valuable, but in the case that somebody is not able to do so, I know that I feel lost when I go back to class, even after reviewing the lecture notes online. I specifically had problems with the last 4/5 essay questions on the homework this past week. Maybe you could post a more detailed outline or something online. Maybe this is too much to ask, but I just feel lost after missing thursday's class. Thanks.

Sorry you couldn't make class. best is to attend a help session or office hours.... and then in retrospect to review the detailed hw solutiosn that are on our website.

I really enjoyed the lecture about exponential growth. I heard before that at some point growth would plane out or the pattern would change when population got to a certain point given a certain size environment. Is this true?

Absolutely true (if I interpret your question correctly). Eventually we will not have enough energy / food for everyone. Either we will curb population growth or the planet will do it for us...

With all the talk on electrons, electricity, capacitors, insulators, diodes, and voltage I feel as if I could almost leave physics 1020 and start by own power or electricity company. Is this true? Maybe in class a description of how we can use the information that we've obtained throughout the semester to our advantage. Good class.

Thanks... yes indeed, you are supposed to apply the stuff you learn --- and perhaps most importantly to apply the techniques of reasoning, justification, argumentation, estimation to the rest of the world / question/ challenges you find yourself in... I promise they'll be helpful.

Indeed ... Great class everyone. Thanks for a fabulous semester.