rallain | January 2, 2010I have been meaning to write about this for quite some time. Really, I wanted to reply to Chad's article on science at Uncertain Principles, but you know how things go. So, here are my key and interesting points about science in random order.
Science is all about models (not ball bearings)
Science is about making models. What is a model? A model can be lots of things. It can be a mathematical relationship, a conceptual model, or even a physical model. One model I like to use is static friction. For many cases, the frictional force can be modeled as:
This model says the frictional…
rallain | January 1, 2010It's odd that I have talked about these forces so much. First, I talked about how centrifugal forces were not real and the difference between centrifugal and centripetal forces. Then I talked about how sometimes, fake forces are good. Finally, I talked about the origin of the words centrifugal and centripetal. (note: "talked about" means wrote a blog post)
In thinking about centripetal forces, I realized that I could come up with a situation in which the centrifugal force is the centripetal force. This is great. I can end all the confusion between centrifugal and centripetal by making a…
rallain | December 31, 2009My brother started blogging. I encourage this kind of behavior. His blog (bluerope.org) is mostly about cocoa programming (which he seems to be fairly competent at). Anyway, I wrote this comment on his first post.
"I applaud your effort to begin a blog again. If everyone had a blog, this world (the internet) would be a better place. Just remember, the first person you are writing for is yourself. Even if no one else ever looks at this, it should still be useful to you. The next person you are writing for is that one person that has a particular problem that you just solved.
I still don't…
rallain | December 31, 2009A couple of commenters expressed concern over the use of centrifugal force after my rant on the use of the word force. So, what is the deal with these two terms? Are they ok to use? Are they real forces?
First, are they real forces?
It depends on what you mean by real. What is a force? Here is a quick overview of what a force is. I previously talked about real vs. non-real forces. For me, I say that if the force is essentially one of the 4 fundamental forces then it is "real". With this definition, centripetal force would be real and centrifugal not real.
Centripetal Force
Centripetal…
rallain | December 30, 2009Some time ago, I wrote about the awesome things the Greeks did in astronomy. Basically they calculated the size of the Earth, distance and size of the moon and distance and size of the sun. The value obtained for the distance to the sun was a bit off, but still a bang up job if you ask me. (where bang-up is meant as a good thing) If the greeks were in my introductory physics lab, they would need to include uncertainties with their measurements. What would the uncertainty in the final value look like?
In my introductory physics lab course, I have students measure things and estimate the…
rallain | December 29, 2009I saw this post about Panasonic's home battery. The claim is that this will lead a battery that can power a house for a week. I wonder if I can estimate how big this battery would be.
First - to estimate the energy a house consumes. My first approximation is that you could probably run a house off of a 5000 Watt generator, but this probably isn't the average power use for a house. It is probably lower. I am going to go with an estimate of 2000 Watts as the average power over 1 day. How much energy would this be for 1 week?
The article above claims that it is a lithium ion battery.…
rallain | December 29, 2009This idea comes from my friend Thomas. His son is like mine in that they both think LEGO are awesome, and they are correct. For some reason, Thomas decided to calculate the price per piece of LEGO in each set. To promote repeatability, I decided to do this also. Looking at the catalog at LEGO.com, I can get both the price of each set and how many pieces it has. Just a note, I looked at almost all of the Star Wars LEGO series and some other select themes. I didn't include any sets that had been marked down in price. I will put the first plot on down below, maybe this would be a good…
rallain | December 28, 2009What happens when your kids won't give you a turn on the Wii? Simple. You take their LEGO bricks and their slinky and do some physics. I will keep this simple. Basically, I created a slinky holder out of LEGO pieces and added LEGO bricks to the end to stretch it. Here is the video.
Lego + Slinky = Physics from Rhett Allain on Vimeo.
Maybe in an un-Dot Physics fashion, I am not going to analyze this data. I am not going to even describe the physics. Instead, I will leave this as a What Can You Do With This in the style of Dan Meyer.
I will give a couple of hints. First, I put this on…
rallain | December 28, 2009One of things I like to think about in science is "how do we know that?" It is interesting how one thing builds on another. This is a story of how the Greeks estimated the distance from the Earth to the Sun (an important idea in the development of the model of the solar system). I like this story because it is not too complicated. In fact, one could easily reproduce these measurements themselves. So, here is what I will talk about:
Measuring the size of the Earth.
Determining the distance from the Earth to the moon and the size of the moon.
Calculating the distance (and size) to the Sun.…
rallain | December 27, 2009In part I of this post, I talked about the basics of projectile motion with no air resistance. Also in that post, I showed that (without air resistance) the angle to throw a ball for maximum range is 45 degrees. When throwing a football, there is some air resistance this means that 45 degree is not necessarily the angle for the greatest range. Well, can't I just do the same thing as before? It turns out that it is a significantly different problem when air resistance is added. Without air resistance, the acceleration was constant. Not so now, my friend.
The problem is that air…
rallain | December 26, 2009On a previous episode of The MythBusters, Adam and Jamie made a lead balloon float. I was impressed. Anyway, I decided to give a more detailed explanation on how this happens. Using the thickness of foil they had, what is the smallest balloon that would float? If the one they created were filled all the way, how much could it lift?
First, how does stuff float at all? There are many levels that this question could be answered. I could start with the nature of pressure, but maybe I will save that for another day. So, let me start with pressure. The reason a balloon floats is because the air…
rallain | December 25, 2009So, analysis of the movie Up is pretty popular in the blogosphere. Figure I might as well surf the popularity wave. So, I have a couple more questions.
The most important thing to estimate is the mass of the house. I am going to completely ignore the buoyancy of the house. I figure this will be insignificant next to the buoyancy needed. Anyway, let me go ahead and recap what has already been done on this in the blogosphere.
Wired Science - How Pixar's Up House Could Really Fly - from that post:
First, they calculated (seemingly correct) that the buoyancy of helium is 0.067 pounds per…
rallain | December 24, 2009Which wastes more fuel? (and thus produces more carbon dioxide). This is a difficult to question to answer for a variety of reasons. The main reason is that a speed change from 71 mph to 70 mph is different than a reduction from 56 to 55 mph.
First, let me be clear that the question of how much fuel is wasted using daytime running lights (or DRL as they are called) has already been addressed. The first source I found was howstuffworks.com
Assumptions
The daytime running lights on a car run at about 100 watts (for the pair)
The energy density of gasoline is 1.21 x 108 Joules/gallon.
A car is…
rallain | December 23, 2009One of my students showed me this game, Fantastic Contraption. The basic idea is to use a couple of different "machine" parts to build something that will move an object into a target area. Not a bad game. But what do I do when I look at a game? I think - hey! I wonder what kind of physics this "world" uses. This is very similar to my analysis of the game Line Rider except completely different.
Fantastic Contraption gives the unique opportunity to build whatever you want. This is great for creating "experiments" in this world.
The first step is to "measure" some stuff. The game…
rallain | December 22, 2009I re-watched Harry Potter and the Order of the Phoenix last night and my wife and I noticed something about teaching. Of course I mentioned that this would make a good blog post (and she may still post it on her blog, but I can't help myself). If you have not read the book or seen the movie, I don't think I will give away any serious spoilers - but who hasn't at least seen the movie? If you were going to see it (or read it) you would have done so by now - right?
The Order of the Phoenix shows at least three different examples of teachers and teachings in the movie. Here they are:
Dolores…
rallain | December 22, 2009Haiku:
The daylight grows short
Blogging time is scarce for now
Repost is now here
I am ready. Bring on the comments about the proper way to write a haiku. Of course, I should warn you that I am technically a professional Haikuer - here is my winning entry to ThinkGeek's haiku contest
Here is the deal. I am going to pick 12 posts from my old stuff and post 1 a day for 12 days (hopefully). Yes, technically, this is not the 12 days of Christmas. Also, I have some other stuff that I am working on, so don't worry - it is not ONLY reposts in the next twelve days.
Anyway, I figure some of you…
rallain | December 22, 2009Female Science Professor has been talking about student evaluations lately. (here are some other Student Eval posts - post 1 post 2 post 3). I had some ideas on student evaluations, and here they are.
One Question
A friend of mine likes to say that student evaluations should just be one question: "Do you like this instructor?" Maybe that is the only reliable information you can get from a student. Perhaps that can even be useful. Here is an indication of the problem. We have on our evaluation form (which is filled with useless questions) the following question:
Agree-Disagree:…
rallain | December 20, 2009This is one of my favorite demos. I like it because anyone can do it at home and people usually find the results surprising. Here is the situation:
How much of yourself could you see in a small mirror? What if you move farther away from the mirror, can you see more of yourself? If you want to do the demo yourself, now would be a good time. All you need is a small mirror (I used a platter from a 10 GB hard drive - they make awesome mirrors). It will help out a lot if you can mount the mirror on a surface that is very near to vertical.
Here is my version of this demo (in case you can't…
rallain | December 18, 2009Fight Science is an entertaining show. Great graphics. The basic idea is to look at the science in different fighting styles. They had a clip-style commercial on it during a MythBusters episode I was watching. And from that, I can say that the kicking looked cool, but the science needs some work.
The Setup
The basic idea is that they wanted to compare kicks from different fighting styles. From what I can gather, they collected data by having some dudes kick this "kicking bag". During the kick, they measured the force exerted on the bag and they had a sensor on the kicker's leg - I…
rallain | December 16, 2009Maybe this could fall under my "physics of parkour". It could also apply to the MythBusters "dumpster diving" episode. In both of these cases, the question is: how far can you jump off of something and not severely hurt yourself. They do this a lot in parkour. Here are some examples:
There are a ton of these things on youtube. Let me go ahead and say it. I would not recommend trying any of this stuff. Even reading this blog won't adequately prepare you. So, if you go ahead and try to do some cool jump, don't blame me for your injuries.
Now that the warning is out there - let me get on…