kinematics
drorzel | August 12, 2011I am an inveterate driver of "back ways" to places. My preferred route to campus involves driving through a whole bunch of residential streets, rather than taking the "main" road leading from our neighborhood to campus. I do this because there are four traffic lights on the main-road route, and they're not well timed, so it's a rare day when I don't get stuck at one or more of them. My preferred route has a lot of stop signs, but very little traffic, so they're quick stops, and I spend more time in motion, which makes me feel like I'm getting there faster.
That's the psychological reason, but…
rallain | September 9, 2010Through random surfing, I found this clip from The Amazing Race (which is apparently some type of reality show). Don't really know the set up except that it appears some girl is trying to launch watermelons with a slingshot. This looks bad, but she seems to not be seriously injured.
Watermelon smashed on face. Wow. What can I we calculate here? Bring in the video analysis.
How fast was the watermelon going?
First, this is not a very good quality video. The frame rate sucks and there is a very slight panning and zooming (which I will ignore) Second, I really don't have anything to scale…
rallain | September 8, 2010Actually, it should be called Happy "Magnitude of the local Earth gravitational field" day. You know, 9.8 N/kg on September 8 (9/8). Get it? Well, the idea was for the physics students and faculty to build some stuff to do outside - projectile motion type stuff. Well, we had the idea a while ago and then kind of forgot about it.
In order to just get something done, I set up the "shoot the falling target" demo. (previously known as shoot the monkey). Here is a quick video demo (seriously - first take too).
What is going on here and what does this have to do with g? Well, it doesn't…
rallain | August 20, 2010Reader Jorge has also looked at these amazing basketball shots. (here is my last basketball analysis) Jorge claims that at least one shot seems fake. He is referring to the following video (at around the 2:20 mark).
ARRGH Ok, new plan. For some dumb reason, youtube won't let me embed this video. Well, here is a link - Amazing Basketball Shots: The Legendary Shots 4 (at least I can link to the right time). It is even dumber that you can't embed it, but youtube gives you the download option. Oh well.
Let me tell you the part that Jorge has an issue with. This guy on a ladder throws a…
rallain | August 13, 2010You know I have trouble letting stuff go, right? I am still thinking about these crazy long basketball shots. Here are some more thoughts.
Really, there are two things I am interested in. First, commenter Scott Post suggests that the drag coefficient might be around 0.25 instead of 0.5. I don't know. For the discussion before, it doesn't really matter. My point was to see a numerical model for a falling ball would be similar to the time and distance from the video. Changing the drag coefficient to 0.25 gives values that are still close to the video. So, I still think the video is real…
rallain | August 5, 2010This is a classic problem. You are in a car heading straight towards a wall. Should you try to stop or should you try to turn to avoid the wall? Bonus question: what if the wall is not really wide so you don't have to turn 90 degrees?
Assumption: Let me assume that I can use the normal model of friction - that the maximum static friction force is proportional to the normal force. Also, I will assume that the frictional coefficient for stopping is the same as for turning.
Stopping
I am going to start with the case of trying to stop. Suppose the car is moving towards the wall at a speed…
rallain | July 13, 2010The other day I found myself faced with six equations that needed to be solved algebraically. Just so you know, I am a big fan of paper for most of these cases - but this was out of control. I was making silly mistakes and causing all sorts of problems. What to do? My first though was to use some symbolic plugins for python. I tried sympy and it is nice. However, it was not giving correct solutions for solving 3 equations - I don't know if this is a bug or what.
Maxima
I think I found Maxima through Wikipedia's Computer algebra system page. It's free and free and runs on Mac OS X and…
rallain | June 8, 2010Well, maybe that isn't the best title. You see, there is this video going around saying that it is possible that a professional bike racer was cheating by putting a hidden motor in his bike. I am not really going to talk about the cheating aspect (my gut feeling says that it would be too easy to catch, so he is not cheating).
Actually, there was an interesting analysis by Ron at CozyBeeHive. Quite a thorough job. He even used Tracker Video Analysis. However, he didn't use some of the nicer features of Tracker, so I figured I would do this analysis also. Plus, you know I love bikes.…
rallain | June 4, 2010Honestly, I was going to add this to my previous post about the jumping car but I didn't because I wanted to finish. So, here it is and more. Actually, I will just make a projectile motion spreadsheet. That way, anytime you want to do a projectile motion problem, you can come here. Maybe this is a bad idea, but I am going to do it anyway.
To start with, I will just say that for projectile motion the horizontal and vertical motions are independent (except for the time it takes). If you want a refresher on projectile motion, here you go. Oh, a couple of assumptions:
Object starts at x =…
rallain | June 3, 2010Reader Colin asked a great question about this popular clip.
How fast was the car moving?
First, a quick assumption. I will assume that the frame rate on the video is correct (meaning not slowed down). Colin already looked up the length of the Chevy Impala on Wikipedia for me. It has a length of 5.09 meters (I need that to scale the video).
This is the data I get from Tracker Video. The graph below is the x-position of the car with a line fit to the part of the motion before it hit the "ramp". Note that since the car is moving to the left, it has a negative x-velocity.
So, this says the…
rallain | May 27, 2010I don't know why they call it a tail drop. Here is a video:
The link I clicked that brought me to this video said the equivalent of "OMG!" That is not what I thought, really I am not sure what is so impressive (except that he didn't fall off the skateboard). If the original poster was impressed with the height of the fall, he clearly has not seen the 35 foot jump into 1 foot of water by Professor Splash.
Anyway, it seems like a simple video to analyze with Tracker Video Analysis. Mostly because the camera is stationary, there is little perspective problems and the motion of the object is…
rallain | May 16, 2010I am excited. This Wednesday, the MythBusters are doing the giant water slide jump. Maybe you are new to the internet and you haven't seen this video. Here it is:
And since it is as old as the hills, of course I have already analyzed it - actually twice. First, the video is fake - but it is an excellent fake. Here is another site with details on how this was created.
What did I look at in my previous posts? Here is a summary.
The video is difficult to analyze because of perspective changes.
Even with these problems, nothing says it has to be fake. The vertical acceleration during the…
rallain | May 5, 2010I was going to make this as a video tutorial, but it just didn't work out right. So, here it is in blog post form.
How do you deal with a video that zoom and pans at the same time? You could keep on adjusting the coordinate axis AND adjust the scale for each frame - but sometimes that is not possible. Tracker Video has a great tool to handle these types of videos - the calibration point pair. The basic idea is that you identify two points in a scene that should be stationary (part of the background) and track those two points. Tracker will then adjust the coordinates and scale to make…
rallain | April 28, 2010Normally, it isn't really news when a show doesn't do anything wrong. I am making an exception for ESPN's Sport Science. Here is part 2 of Sport Science trying to reproduce Kobe Bryant's "jumping over a car" stunt.
And here is part 1 (although part 2 is the only interesting part). See. I can get along with Sport Science. Anyway, I am not sure that Kobe's jump used wires - but I assumed it was fake. Here is my analysis of Kobe's Jump (this stuff is old). And this is the plot I created from video analysis of Kobe.
The tough thing about looking at Kobe's jump is that he changes his body…
rallain | April 24, 2010Check this out.
So, the guy jumps from 150 feet into some cardboard boxes. Why are the boxes important? You want something that can stop you in the largest distance to make your acceleration the smallest. Here is my Dangerous Jumping Calculator. Basically, you put in how high you will jump from and how much distance you will take to land and it tells you your acceleration.
You will probably need this G-force tolerance info from wikipedia.
One problem - this calculator doesn't really work for this case. It doesn't take into account air resistance. Does air resistance even matter in this…
rallain | March 29, 2010Here is a quick Apolo Ohno quiz. Which one of these pictures is fake?
If you picked picture B - you are probably correct. That is a picture of "Apolo" being catapulted into a pool of slime at the Nickelodeon awards show (click on the link to see the video - I don't think I can embed it). Ok - time to crank out an analysis.
I think I could approach this analysis from a couple of directions. Since all I have is a crappy version of the video, I could just look at "could this be possible"? The other analysis I could do would be to measure his acceleration in free fall. Let me start with…
drorzel | February 16, 2010Boskone this past weekend was held at the Westin Waterfront in Boston, which has these funky double showerheads that they charmingly call the "Heavenly(R) Shower" (hype aside, they are very nice showers). The picture at right is courtesy of lannalee on Twitter, as I didn't bring a camera.
Why am I telling you this? Because there was a sign glued to the wall in the shower that read:
Refresh yourself, restore our world
One of your Heavenly(R) Shower heads has been turned off in an effort to minimize water usage and protect one of our most precious natural resources.
The smarmy enviroweenieness…
grrlscientist | January 28, 2010tags: kinematics, kinetics, running,The Barefoot Professor, exercise physiology, barefoot running, NPG, peer-reviewed research, NATURE, 10.1038/nature08723, streaming video
Harvard professor Daniel Lieberman ditched his trainers and started running barefoot. His research shows that barefoot runners, who tend to land on their fore-foot, generate less impact shock than runners in sports shoes who land heel first. This makes barefoot running comfortable and could minimize running-related injuries.
This video is interesting to me because I was a cross-country runner and later, a long-distance…
rallain | January 20, 2010I stumbled on this flash game Bloons. The basic idea is that you (the monkey) throw these darts and try to pop some balloons.
Well, what is the motion of these darts like? Is it constant acceleration? Time to pull out the free and awesome Tracker Video Analysis.
I threw a few shots and captured the screen with Mac OS X's quicktime X (which does screen recordings now). Then I chose a few of the motions to analyze. I was going to use Tracker's autotracker feature, but I am not sure how well it would work since the dart changes orientation (of course I didn't even try this to see if it…
rallain | January 19, 2010My dad and I had a disagreement. We were driving back from a trip and he let me take over the wheel for a while. His complaint was that I was driving too slow and it was driving him crazy. For me, I thought I was driving fast. My typical behavior is to drive 3 mph under the speed limit. That is just how I roll. In this case, I knew he wouldn't be able to handle this so I went the speed limit (70 mph).
Here is the problem. The speedometer said 70 mph. The gps thingy said the average speed was 69 mph. I think my dad feels that the gps is correct and that cars have speedometers that are…