rallain | August 18, 2009I got this question. How does this game work? Really, this is one of those silly things that gets forwarded a lot. It is called Regifting Robin. The basic idea is:
pick a 2 digit number, like 37
subtract both the number in the tens place and the number in the ones place from the original number
find the number you have left on a grid of "gifts" and robin will guess what your gift was
You may have seen stuff like this before and figured it out. It really isn't too bad as long as you know two things (one is a trick)
In a two digit number, like 37, the number is really 3*10 + 7*1. I know…
rallain | August 18, 2009I wrote two letters (for two different classes). These are letters from the students of the near future to themselves in the present. this first one is for a non-majors lab. In this lab, I let them turn in "informal" lab reports that they can then use on the midterm and the final exam. The thing is that a lot of students don't even turn this in. Here is the letter:
Dear Past Me,
How are you? I know how you are because I am you and I remember this day. Really, you should be asking how I am.
I am not doing so well. I just took the midterm for the physics lab and it didn't go too well.…
rallain | August 17, 2009I have been reflecting on my recent failure to realize that the Giant Water Slide Jump was fake (more analysis here). I think the guys that made this video did a really good job on several levels. First, the motion appears to do two important things:
shows constant acceleration in the vertical direction
shows constant velocity in the horizontal direction
That seems like such a simple thing, but it is surprising how often fake videos don't have those two elements. Maybe they were not close, but with the error associated with the panning and zooming camera, it seemed close enough. Also, to…
rallain | August 17, 2009This is amazing. I can't believe that power companies are paying Blacklight Power money, but they are. I guess Blacklight Power must have great advertising. Ok, so what is this whole Blacklight-hyrdino thing? Honestly, I am not fully familiar with it, but basically this guy says that you can get energy by getting the electron in hydrogen to go to a lower energy level than ground state. Here are a few good links regarding this hydrino stuff.
Six Tiny Utilities Buy "Scientifically Impossible" Energy: CleanTechnica
Blacklight Power claims nearly-free energy from water - is this for real? |…
rallain | August 13, 2009What's the deal with the Chevy Volt? Well, obviously, it is a cool car. A plug-in hybrid. The problem is in how to quantify its efficiency. Normal hybrids (the non-plug in type) have only one type of energy input, gasoline. The Volt can take gasoline or electricity input. This makes it difficult to compare the efficiency of other cars. What is efficiency? There are several things you could calculate.
Actual MPG
This is the distance the car travels (the miles part) divided by how much gasoline it used (the gallons part). Pretty straight forward? Ah ha! Not so straight forward for…
rallain | August 12, 2009This Giant water slide video is extremely popular on the internets. Maybe you have not seen it (doubtful), then here it is:
This is such an incredible stunt that the very first question that comes up is - fake? or not fake? From my previous analysis, I can say:
Even though there is some slight perspective issues, the vertical acceleration seems to be constant and has a reasonable scale to give the acceleration of -9.8 m/s2
The horizontal motion is essentially constant (as a real jump would be)
The launch speed is about 19 m/s
The launch angle is 32.8 degrees
If the guy had no friction on…
rallain | August 7, 2009I have previously compared Tracker Video Analysis and Logger Pro - check that out here. Really, the only advantage Logger Pro has over Tracker is that maybe it is easier to use for simple things and maybe students are already familiar with it from other analysis.
There are other video analysis programs out there. There is VideoPoint - but this is not free and I don't think it has been updated in quite some time. Also, don't forget Video Graph. A great program for it's time, but that time was 1997.
So, this post is really about Tracker and its feature of calibration point pairs. What is…
rallain | August 6, 2009Thanks to Nick for showing me this video (Check out his blog - Fine Structure):
See more funny videos and TBT Videos at Today's Big Thing.
Wow. That was my first reaction. My second reaction was: no way. Is this real life? I just don't know. How hard would it be to find out exactly where to place that pool and where did they get the water from? Obviously, this one requires some analysis. First, on the VAS for this video: 4/8. Not too good. Oh here are the questions I would like to answer:
What is the guy's acceleration after he leaves the ramp?
What was his initial velocity leaving…
rallain | August 5, 2009I keep saying the same stuff over and over when it comes to analyzing videos. I can't immediately find a post that lists what makes a video acceptable for analysis, so I will just reproduce on here. I will give 1 point for each of the following that the video has:
Stationary camera and background
Camera does not zoom
Motion perpendicular to the camera
You can see the object in every frame (nothing obscuring the motion)
Interesting physics content
Downloadable (some videos I can't "get off the web")
No repeating frames
Not badly interlaced (or would that be deinterlaced - I get confused)…
rallain | August 5, 2009Parkour: the act of running and jumping like a crazy superhero. I can't do any of it. But I can analyze it. So, let me start with the wall-flip (or any kind of move that involves walking on vertical walls). This looks like a good example (there are a bajillion on youtube).
Pretty cool, huh? How do you run up a wall? Well, it has to do with friction. Remember, this is a fairly useful model for the magnitude of the frictional force on an object:
Where N is the force the surface exerts on the object (the normal force) and ?s is the coefficient of static friction. Note that this less…
rallain | August 4, 2009Check this out (saw it on the interwebs):
It's this video inside a bus of a girl hitting the roof. My first thought was: well, she just jumped. But something was odd. She was in the air too long. Well, of course this calls for a video analysis (using Tracker Video Analysis). Actually, it is a good candidate for analysis. Primarily because the motion happens right next to the back of the bus and the bus can be considered the reference frame. The only problem is the scale. I totally guessed that the back window was 3 feet, but not sure this even matters. Here is the motion of the girl…
rallain | August 3, 2009Every introductory astronomy text and most intro physics texts talk about tides. The usual explanation is something along the lines of:
The moon exerts a gravitational force on the Earth and all the stuff on the Earth.
This force decreases with distance (1/r2).
Thus the moon pulls greater on one side of the Earth than the other
This doesn't matter except for oceans which can move.
BOOM. Two tides a day due to a bulge on the side close to the moon and the opposite side.
Oh, the Earth is slowing down.
Really, that is what almost all intro texts say. Go check for yourselves.
Yes, the tides…
rallain | July 31, 2009Two things. First, my wife started blogging. The best thing about this is that she can no longer complain about my blogging. Her blog is over at HyperHomeschool.com. Basically, she is keeping up with her homeschooling stuff online. I see great potential here.
I guess this gets to the second thing. I made a little screen cast tutorial on Scratch. I figured this would be good material for her blog. In case you are not familiar with Scratch, it is a graphical programming language developed at MIT. It is very similar to the Lego Mindstorms programming language. You can do tons of stuff…
rallain | July 30, 2009The fall semester is coming up soon. Some students will be taking physics in college. So, here are some pre-class tips - mainly aimed at college students taking algebra-based physics.
Are you afraid?
If you are reading this, maybe you found it because you were looking for stuff on physics. Maybe you are a little scared. You have heard physics is a tough course. Well, that is only kind of true. First, the fear thing. Use it to your advantage. Let fear be a motivator to help you keep up with the class. I think that is the biggest mistake students make. They think of intro physics as…
rallain | July 30, 2009Still moving stuff over from my last server. Here is one that keeps coming up.
Surprisingly, I STILL get comments and questions from students and teachers about Pluto. Questions such as:
"Why do scientists hate Pluto?"
"How did they discover that Pluto was not a planet"
"What will happen to our planet songs without Pluto?"
"Why does Goofey wear clothes, but Pluto doesn't even though they are BOTH dogs?"
Here is the explanation I like to give. I like to start with the following question:
Suppose you were outside and saw this (image from wikimedia):
What would you call it? Some might call…
rallain | July 29, 2009I am not a programmer. Just to be clear. I use python to get things done, but I am sure it could be done in more efficient ways. Anyway, I sure you know how much I like vpython - especially for teaching physics. However, sometimes I use it for blogging stuff also. The problem is that vpython doesn't make pretty graphs. Oh, they are quick and simple - but sometimes you want pretty also. Well, what if you just don't use vpython? Of course then I could use some other plotting package like pylab (which actually uses something else like matplotlib or something - I get confused). Or, I…
rallain | July 29, 2009You have no idea how long I have been sitting on this one. I made some videos like a billion years ago, and still no post. Why? Oh well, here it is.
I like video analysis of motion. I like looking at stuff on youtube or other video sites. But sometimes, you need to make the video yourself. What should you use? My personal favorite is a Flip Mino HD. It is small and quick. Are there other options? Sure. In this post, I will do the video analysis with the following cameras:
Flip Mino HD
A Canon PowerShot A470
Panasonic DMC-FZ18
Canon HV10 HD miniDV camcorder (you know, the kind that…
rallain | July 28, 2009Thanks to reader Cleon for notifying me of this video on youtube. Check it out.
First, some notes.
I am sure you noticed that the aspect ratio is incorrect (at least that was the first thing I noticed). The boys must have made a 16:9 video, but then uploaded it to youtube as a 4:3. This doesn't really affect the analysis, but I had to fix it. I used the awesome firefox plugin NetVideoHunter to download the video and then used MPEG Streamclip to resize the video.
Other than that, they did follow my suggestions for making videos. The camera doesn't move and is mostly perpendicular to the…
rallain | July 27, 2009Sciencegeekgirl is blogging from the AAPT. She talks about showing something interesting to get students thinking, and here is her example:
This reminds me of Dan Meyer's What Can You Do With This stuff. Anyway, I can't help it. I must analyze this video. Plus, Fran essentially threw down the gauntlet and called me out on this move. Another reason to analyze this movie is that it is obviously fake. Elephants are one of the few animals that can't jump. Not even a little bit. They don't like to have more than 1 foot off the ground. Ok, on to the analysis. As usual, I downloaded the…
rallain | July 25, 2009Here is an interesting article from Mashable: In the Future, the Cost of Education will be Zero
In the article, the author Josh makes the following points:
College is expensive and some people can't really afford it.
There is a growing trend in online universities. University of the People is one example.
Other universities are putting a lot of their material online - example MIT's OpenCourseWare project.
There are a growing number of free textbooks available online. I would like to point to an example of a free physics textbook.
Josh also points out that everyone should have a chance to go…