kinematics
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 | 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 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 16, 2009Yesterday, I uploaded a post from my old site about slowing down time to make videos look like they were on the moon. If you haven't read that, the short story is that it doesn't look right when speed Apollo videos up so that the acceleration is -9.8 m/s2.
What started that whole thing was an even earlier post. Here is an example of using video analysis (Tracker Video Analysis) to measure the acceleration of a jumping astronaut on the moon. In this case, it is the famous "jump salute" from Apollo 16 astronaut John Young.
First, thanks John (or whoever videoed it). This is a good video for…
rallain | July 15, 2009Note: This is a repost from my old site. Time to move it over.
First, what is different about motion on the moon and on Earth? Since the moon has a smaller mass in spite of its smaller size*, the moon has a smaller gravitational field. The gravitational field on the surface of the moon is 1/6th the field on the surface of the Earth. This means that the acceleration of a free falling on the object would be 1/6th the acceleration on Earth. So the question is: how would you change the time scale of a movie so that it looks like its acceleration is 1/6th of 9.8 m/s2?
*If you make the size of…
rallain | July 4, 2009I created another screen cast showing how to get started with a numerical calculation for one of my classes. In this case, the students are attempting to model the motion of an object falling with air resistance. The following example doesn't show the steps including the air resistance, but maybe it is enough to get someone started.
Record your screencast online
rallain | June 24, 2009I made this screen cast for my algebra-based lab. Maybe you will find it useful also. This is a tutorial using Tracker Video Analysis (an awesome free program as I have said many times). In this tutorial I analyze a moving cart that shoots a ball up and lands back in the moving cart (called a Howitzer cart). The video is available at the LivePhoto Physics site.
Screencasts and videos online
rallain | June 3, 2009I haven't seen the Pixar Movie "Up" yet, so don't spoil it for me. I have, however, seen the trailer. In my usual fashion, I have to find something to complain about. There is this scene where the old man releases balloons out of the house.
What is wrong with this scene? Also, would that be enough balloons to make the house float? Here is a shot of the balloons coming out of the house.
Ok, I was already wrong. The first time I saw this trailer I thought the balloons were stored in his house. After re-watching in slow motion, it seems the balloons were maybe in the back yard held down…
rallain | May 29, 2009My brother found this, but he is too afraid of the internet to post something in the comments on my previous post about acceleration and the iphone. It turns out that this too awesome to just be in a comment. It deserves its own note.
Anyway, I was looking for acceleration data from the iPhone and this guy put one in his model rocket.
iPhone Rocket Launch and Interview (from MobileOrchard.com) from Mobile Orchard on Vimeo.
Here is some more detail (with graphs!) about the iPhone model rocket.
rallain | May 29, 2009Here is another one from a great podcast - Buzz Out Loud. I totally can't remember which episode it was, I listened to a several in a row mowing the lawn and doing outside type work. Anyway, the discuss was along the lines of:
Could an iphone tell if your parachute didn't open with its accelerometer?
The first and simplest answer would be "no". When you are skydiving, you quickly reach terminal velocity such that you are no longer accelerating. Maybe the built in GPS could use elevation data, but it seems like that is rarely used (and not very accurate). There is perhaps a way that work…
rallain | April 30, 2009ZapperZ already beat me to this, but if it is worth doing once it is worth doing again. Here is a video of an electric motorcycle that can apparently go from 0 to 60 mph in 1 second.
What acceleration would this have? If you want, you can look at my stuff on kinematics, but this case is pretty straight forward. Really, as straight forward as one could get. Let me start with the definition of acceleration: (in the x-direction since this is a 1-d problem)
I know both the change in speed and the time, so this is easy. I can make it even easier using google. The acceleration is 60 mph/s.…
rallain | March 25, 2009Dan Meyer made this awesome photo. He posted it so that others could look at it and come up with lesson ideas to use with this. There are some very good suggestions in his comments. I wasn't going to analyze this because I didn't want to rob some students of the opportunity, but I can't resist. Also, I doubt the first step a student would use would be to google for the answer. HA! I just caught you, you googling student.
Ok - I will try not to post any data. However, I will post some info on how I analyzed this.
The photo is a composite image from a video clip of a person throwing a…
rallain | February 17, 2009The first thing from AAPT that I would like to mention is SAM Animation that Brian Gravel demonstrated. SAM is free software that allows for the easy creation of stop motion animations. Basically, you use a web camera to take successive pictures and put them together as a movie. The software includes features (I think they call it an onion view) to see your previous frame while you are making the next frame. I think the software also lets you do time-lapse videos (which I think are awesome but they take lots of patience).
Fine, it is cool, but what do you do with it? Besides make movies…
rallain | February 2, 2009I enjoyed the super bowl commercials for the most part. You have to be careful not to have too high of expectations, or you will set yourself up for a big letdown. Here is a quick analysis of one of the commercials. This is a Bud Light commercial where at the end they throw a guy out of an office window because he suggests they save money by not buying beer. Are there any actual office meetings that serve beer? (Sorry if I spoiled the ending for you)
I am going to analyze the motion of the guy going out the window. Just because.
At some point in the future, I am going to make a short…
rallain | January 29, 2009I really didn't want to post this, but I am going to anyway. I used ScreenToaster.com to make a screen capture movie (with audio) of a tutorial on spreadsheets.
This should accompany my previous post on numerical calculations.
Free online screen recorder
rallain | January 27, 2009We have all seen the Kobe Bryant video of him jumping over an Aston Martin - this keeps coming up on the Internet. There has been vast discussions of whether this is real or fake. I will do my best to examine the evidence. In short (in case you don't want to read the whole thing) Kobe can most likely really jump that high, it is possible that there was some perspective trickery involved. Here is the video in case you are brand new to the WWW:
Oh - don't forget I already analyzed Kobe Bryant jumping over a pool of snakes. I voted that was real.
First, let me give a personal note to Kobe and…
rallain | January 16, 2009It has been windy here lately. Sometimes I think that is an ok thing. You see, when I ride my bike to work I am probably going to have the wind at my back for one of directions. It is great feeling like Lance Armstrong because of the boost you get from the wind. With a good wind at my back, I can almost keep up with the traffic (I would keep up if they went the 25 mph speed limit).
Of course, with a great boost comes a great drag. When I ride into the wind, I feel weak. I pedal as fast as I can and cars just whiz right by like I am standing still. When you are in a car, you don't…
rallain | January 10, 2009So, here is a video (from break.com - so you know it is likely fake).
null - Watch more free videos
If for some reason, you can not view this video, here is the plot.
Guy wears parachute and brings a portable thing like a see-saw.
Guy approaches large crane dropping a large mass repeatedly (I assume to flatten a dirt road)
Guy sneaks up an puts the see-saw under the area that the mass drops on and then stands on the other end of the see-saw.
Mass drops, guy shoots up and parachutes down.
So, why is it fake? I think the best thing is to give an analysis of the see-saw. To start this…
rallain | January 7, 2009I saw this video posted on Physics and Physicists:
It reminded me that I had at one point tried to analyze this. I had actually posted something about this on the first generation of my blog (which no longer exists). I have found the analysis, and here it is from the archives. Thanks ZZ for reminding me.
Could this be true, or is it fake? I started to do an analysis of the trajectory, but I found the following frames:
Look at the guy's back. His back starts moving before the water bottle rockets. It must be some type of cable pulling him. If the rockets were propelling him, the rockets…
rallain | December 29, 2008In 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…