video analysis
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 | August 24, 2010I might as well make a new tag called "basketball throws" because I can't stop with the analysis of these crazy basketball shots. Watch - in the end someone is going to post a video about how all these were faked (and I have said there is no clear evidence they are fake). Oh, if you want to see some shots that I am talking about - just search for Dude Perfect on youtube.
Physically, these crazy shots are possible. Time of flight in the video is comparable to a numerical model. But, the question is: how difficult are these shots? Are these one in a million? Are they easy? Are they…
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 7, 2010I have seen several videos similar to this.
Real? Fake? How many tries did this take? Let the analysis begin. Before I do any analysis, let me state that I think this is not fake. I do not know that for sure, just my first guess.
How would I tell if it is real or fake? This is tricky. I can't really get a good trajectory of the ball to make some measurements on it because of the camera angle (next time people, make sure you set the camera up perpendicular to the plane of motion and far enough away to avoid perspective problems - thanks!) Really, the best I can do is to look at the…
rallain | July 30, 2010The Lord of the Rings trilogy came on TV again recently. My wife and I can't help but to watch this even though we have it on DVD. Anyway, I was thinking about the part where Gondor sends a signal to Rohan asking them for military aid. Since this was before the invention of email, they had to do it with a signal fire. Hopefully this clip won't be a spoiler for you, but this is from the movie. Actually, all of the clips available have embedding disabled. So this is just a picture of that clip. If you want to see it, go to the youtube version.
One other spoiler: Sauron is really Frodo's…
rallain | July 21, 2010Frank Noschese is a physics teacher and a blogger (and frequent commenter on Dot Physics). And I nominate Frank as the new librarian of videos that can be analyzed for realness or fakeness. Or, as Frank calls them Win-Fail Physics. Note that I sort of changed his theme a little - sorry Frank.
Win-Fail physics videos are all over the place. You know I like these things. They are videos that look cool and people question if they are real or fake. Sometimes it is easy to tell, sometimes it takes a little analysis, and sometimes it is very difficult to tell (and I get it wrong).
So, here is…
rallain | July 13, 2010Here is a commercial for some Mercedes car. The first part is quite boring, but check out the stunt at around 2:00 minutes into the video.
I haven't bothered to check if this is officially fake or not. Instead, I will do what I do - see if this is even feasible.
The common question people ask when they see something like this is: "how does the car defy gravity?" Well, it doesn't. Why doesn't it fall? In a sense it does. This is essentially the same as spinning a bucket of water over your head. Maybe a diagram of the car at the top of the tunnel will help.
I tried to make the car stand…
rallain | June 16, 2010Somewhere on the internet, I came across this Cracked.com article on movie myths about guns. The article wasn't too bad, but I really liked this video they included from Arnold's movie Commando.
The myth for this particular clip was that guns never run out of ammo in the movies. Right away, I thought: I wonder how many bullets he shot? BRING IT ON.
First, I am going to find the fire rate of Arnold's weapon. Oh, I know I could look it up on Wikipedia or something - but I am not going to do that. I am going to determine the fire rate from the clip.
After capturing an audio segment where…
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 20, 2010And there's parliament. Ok - sorry, I had to make a "Tom (Swans on Tea)" title for this one. Tom, forgive me.
Here are two great circular motion videos. First, this one is from Dale Basler. He made himself a fine little floater-type accelerometer. Better than just make it, he made a video of the accelerometer in his car going around a round about. Check it out.
Bobber Meets Roundabout from Dale Basler on Vimeo.
So, if he is driving at a constant 10 mph, how big is the round about (traffic circle)?
Next video - more silly kids
First, I saw this one on ZapperZ's Physics and Physicists who…
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 15, 2010I was going to just leave the oil spill in the gulf topic alone. Not because it isn't important, obviously it is. Rather, I wasn't going to do anything because I didn't really have anything to add to the topic. After a couple of readers requested it, I think I do have something to add. How exactly do you estimate the amount of oil flowing into the gulf?
What do I have to start with? A video. Here is a video of the undersea oil leak.
Now, I am not the first to estimate the oil flow rate (NPR on Purdue Prof's estimation and here a commenter make a quick calculation). Like I said, I am…
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 | May 3, 2010This video seems like it is getting popular, but maybe that is because it is so awesome.
Maybe it is just me, but I find this video very visually satisfying. I love the way they compare the different runners.
Anyway, there is some physics here. Commenter Ben sent me the link to this video (thanks!) with some great questions. Which of the runners has a greater kinetic energy? What about the power? These aren't too difficult to answer, but the first thing is to get the data. There are several options (including just using a stop watch). But no, that is not good enough for me. Instead, I…
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 27, 2010There are several free iPhone-iPod Touch apps that let you look at the acceleration of the device using the built in accelerometer. I was planning on reviewing some of these free apps, but I didn't. When I started playing around with them, it was clear that I needed some way to make a constant acceleration. There are two simple ways to do this - drop it, or spin it in a circle. I decided to go with the circular motion option because I like my iPod and because Steve Jobs told me to.
While playing with this, I realized that the acceleration depends on the distance of the sensor from the…