analysis
rallain | June 22, 2009Maybe this isn't the best video to analyze, but it sure is funny. I am not sure why it is so funny - maybe you should just watch it first.
Sledgehammer Funby Stressmaker
I don't really know why these guys are putting explosive on sledge hammers. Sure it looks fun, but I think I would pass. Anyway, here is the part I was curious about.
Did the exploding hammer lift him off the ground, or did he jump as a reaction to the explosion. It kind of looks like he was lifted, but I am not sure that is possible. Video analysis to the rescue. (using Tracker Video) So, I assumed the sledge hammer…
rallain | June 19, 2009I have been wanting to look at this whole curved bullet thing, but I wasn't sure how to approach it. In case you are familiar with the myth, this is from the movie WANTED (which I did not see). Apparently, some people learn how to make bullets curve by moving their gun. Here is a shot of a bullet curving in front of someone.
Maybe the picture doesn't do the clip justice, but it is enough for you to get an idea. Before I do an analysis, this reminds me of a great educational activity. In the activity, you give groups of students a full sheet of paper with lines that look something like…
rallain | June 12, 2009Jennifer over at Cocktail Party Physics has a nice post about her trip to Disneyland. The one ride that would be fun to play with (in terms of physics) would be the tower of terror. Think of the cool things you could do with a video camera during that ride. It would be like a mini-vomit-comet. Anyway, I want to talk about one part of Jennifer's post.
"As one would expect, this lifted us out of our seats slightly, as much as the straps would allow, and we got that one glorious moment of seeming weightlessness, before reaching a jerky stop and being raised back up for another drop."
It is…
rallain | June 9, 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 | 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, 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 | May 21, 2009I made a gamble and my gamble failed. It really wasn't my fault. In the preview, they showed this huge barrel thing dropping on a see saw. It looked something like this: (I could search for 30 minutes for a picture of this online, or just draw it)
At first glance, this looked JUST like that video of the pile driver shooting the skydiver up in the air. You can see how I would make that mistake. To make up for my mistake, I will give a very simple analysis of the see saw myth. The basic idea is that something comes down, hits the see saw and sends the other thing flying up. If I assume…
rallain | May 18, 2009Another electric motorcycle post. (Here is the post on the wind-recharged drag racing motorcycle) This new one is a solar powered motorcycle. The site claims that the bike can go 50 miles on a full charge (from Gas2.org). This is easily possible, but how long would it take to charge with normal solar panels? Here is an image of the bike.
Questions to be answered: How much energy would the bike need to go 50 miles? How much power (average) could you expect to get from the solar panels? And...how long would it take to charge this sucker. I am sure you can store enough energy in a…
rallain | May 14, 2009I think the Mythbusters have a wonderful opportunity for educational outreach. Take this week's episode. One myth was to see if arrows fired from a moving horse penetrated more than arrows fired from a standing position. They first did this with real horses, but they said the data was not convincing.
I am pretty sure they had more than 10 trials recorded (there was a glimpse of the notebook). I would love to see this data and find (or let students find) the standard error of these measurements. This would be a great exercise to see how this whole uncertainty thing works.
As long as I am…
rallain | May 14, 2009Last night was Wednesday, so of course I watched Mythbusters. You never know when a good blogging opportunity will come up. I could talk about the kinetic energy of arrows, but instead let me talk about their episode for next week. I only caught a glimpse of it in the preview. It looks like they are doing something about jumping on a see-saw and launching the other person. It could be this video they are looking at:
EMBED-Extreme Catapulting - Watch more free videos
From my analysis of this video, I found that the likely outcome was a broken board (if it were not fake). Also, if the…
rallain | May 12, 2009Maybe you have seen this trick. Basically, you hold by supporting it with two fingers from the bottom. You then move your hand around to keep it balanced while the stick is vertical. It is really not as hard as it looks. Also, there are two things that can make your job easier. Use a longer stick, or add an extra mass at the end of the stick. Here is a video of me demonstrating this. (I forgot, this also an event in the show Unbeatable Banzuke)
Balancing a Stick Demo from Rhett Allain on Vimeo.
So, how does this work? Let me start with a stick that is mostly vertical and supported by…
rallain | May 5, 2009I just realized that something has been bothering me. It is this KillaCycle - the electric zoom-fast motorcycle that I posted about previously. It clearly is super fast. However there are two claims that seem iffy.
It can be recharged in 4 minutes.
It is recharged by wind power.
It may be possible that these individually could be true - but could it be recharged in 4 minutes by the wind? I am not sure. Let me do some estimations to see if this is possible. What am I starting with:
From the review on gas2.org, uses cordless drill batteries.
Uses 1200 batteries
Produces 500 bhp - not…
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 | April 21, 2009First: Car Talk is awesome. I wish I could come up with some class activities that help students become as good at trouble shooting and critical thinking as Tom and Ray are. Anyway, they are quite entertaining.
So, my Dad called and told me he heard a discussion on Car Talk about the effect DC to AC converters and accessories plugged in to it and how they would effect gas mileage. I skimmed through the last Car Talk podcast, but couldn't find it. He must have heard a re-run on the radio or something (he doesn't really believe in podcasts). Let me calculate the effect a number of things…
rallain | April 13, 2009Previously, I showed how to analyze a cat video with Logger Pro. Logger Pro is nice, but so is Tracker Video. I also posted a comparison between Tracker and Logger Pro. Now, here is the same tutorial on the same video using Tracker Video.
Record your screencast online
I am not going to go through the analysis, since it would be the same as with Logger Pro.
rallain | April 12, 2009I already talked about increasing the temperature of a pool. My father commented that he thought the pool level rose by like half an inch when the temperature increased (by about 10 degrees F). So, this leaves the question: Is my father crazy, or is this possible? Or are both true?
Does water expand when it warms up? Yes, except when it melts. Why does this happen? Liquids are actually very complicated, but here is a basic answer. Take a look at this PhET gas simulator, I know it is for gases not liquids. I think we can make it behave like a liquid if you increase the gravity to the…
rallain | April 10, 2009I am so pumped up that MythBusters is back on. Not only do I like the show, but it offers so many blogging opportunities. Their latest show featured car crashing myths. One of the myths from the episode was a redo of the myth where two trucks crash head on simultaneously crushing a smaller car in the middle.
The first test was very similar to the previous time they tested this, but faster. They towed two 18 wheelers to crash together around 50 mph and smash a stationary car. The results were impressive. However, they did not have the result of the car completely contained in the…
rallain | April 6, 2009Cats can be entertaining - especially when they are someone else's cat and that someone made a video. Really, this post is about analyzing video with Logger Pro (in a tutorial type fashion). I just happens that I chose this cat video to analyze. Here is the video:
I am going to look at the part where the cat gets on the fan. I will try to step through the analysis so you can do your own.
Get the video
Actually, the first step is to find a video. YouTube has tons of stuff. Also, you could make your own video with a camera. A couple of things to make your life easier:
A non-zoom video.…
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 | March 4, 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…