# analysis

### Watermelon Collisions - ouch

Through 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…

### The Curving Soccer Ball

You can call it football if it makes you happy. Anyway, this is a popular story going around. The physics of the magic curving soccer kick. Here are two ends of the spectrum. First, there is the lower, easier to consume version from io9.com Physics forced to come up with whole new equation to explain "impossible" soccer kick I will summarize this article for you: "Have you seen these crazy soccer kicks where the ball curves? It happens because the ball spins and physics. Here is a video" Oh, and they have a diagram - which doesn't seem to come from the original paper and they also have…

### What if everyone jumped?

Might as well jump. Jump. Go ahead, jump. - Van Halen Suppose everyone in the world got together and jumped. Would the Earth move? Yes. Would it be noticeable? Time for a calculation. Note: I am almost certain that I have done this before, but I can't find where. Starting assumptions. 7 billion people. Average weight: 50 kg (you know, kids and stuff) Average vertical jump (center of mass): 0.3 meters - and I think that is generous. Mass of the Earth: 6 x 1024 kg Gravitational field near the surface of the Earth is constant with a magnitude of 9.8 N/kg Ignore the interaction with the…

### How tall is that UFO?

You know I wander around the intertubes, right? Who doesn't? Anyway, I saw this collection of strange google Earth images. Yeah, it is kind of dumb, but this one made me think: That article said the image was from TechEBlog, so there is that. I have no idea what this thing is, but it is clearly tall. How tall? Instead of searching online for info about this structure (that wouldn't be any fun), I figured I could do a quick analysis of the shadow. Here we go. First, I need to make some measurements. It turns out that Tracker Video tool for analysis is also quite excellent to use for…

### Variation in throwing a ball

I 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…

### More on turning and braking

I can't let it go. There is more here to explore. First, I can't believe that I looked at braking and then turning but not turning then braking. And what about braking while turning? I will model braking and then turning - but it won't stop here. Consider a few motions. I could turn and then brake (which I am looking in this post). Another option would be to brake and then turn. I already showed that this takes a longer distance than just stopping. Braking and then turning in general won't work. Suppose I brake and slow down to a certain speed. Now I am a certain distance away from…

You 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…

### Size of 91,000 documents

Here is a quick one. One of the big news stories recently was this regarding WikiLeaks and the release of the Afghan War Diary. There could be tons of things to discuss regarding this - but I am not going to do that. The first thing that struck my mind was "over 91,000 documents". That seems like a lot. If each one of these documents were printed on one page, how big would the stack of paper be? I could just estimate this - fermi-problem style. But instead, I thought would use a stack of paper. Here is a pack of 500 sheets of paper. Opening it, I can measure the thickness: How thick…

### Basketball shot - real or fake?

I 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…

### How fast is the Beacon of Gondor?

The 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…

### Mercedes Roll

Here 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…

### Chased by a Zombie

Title: Chased by zombies When I heard word about the ScienceBlogs Zombie Day, I knew I wanted to participate with a post - but I had no idea what to do. My first thought was to somehow talk about living off the electric grid in the case of a zombipocolypse - you know, like how big of a solar panel would you need? But you know what? Physics is difficult - but modeling is easy. How about I model something? How about a model for the motion of a zombie horde? This will be great. Zombie motion model What do I want in my model? What are the constraints? What real-life situations can I use to…

### What is Arnold made of?

Of course I am talking about Arnold Schwarzenegger. After looking at how many bullets he carries in Commando, I remembered this scene (also from Commando) (warning: maybe some not great language and some killing. You have been warned) If you don't want to watch that clip, here is a shot (sorry for the quality). Clearly Arnold is strong, but there is more than strength involved here. Oh, don't bring your "he did it with wire stuff". I am not buying that. Also, I am talking about THE Arnold - he is real. I am not talking about the character in the movie (not real). Now for some physics…

### How many bullets did the commando shoot?

Somewhere 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…

### Energy in a hidden battery

Back to the discussion about hiding an electric motor in a pro racing cycle. Before, I looked at a video of Fabian Cancellara to see how his speed and acceleration compare to other bikers. The claim on the internet is that he pulls away so fast that he must have a motor hidden in his bike. Just to be completely clear, I don't think he is cheating. Then why bother? If you ask that then this must be the first time you reading this blog. I welcome you. No, but really, this is what scientists do. How hard would it be to cheat? From my analysis, it seems that a person could ride like he…

### Do Bikers Cheat?

Well, 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.…

### How fast was the car going?

Reader 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…

### Tail-Drop Analysis

I 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…

### How big of a balloon do you need to get to 120,000 feet high?

I am still thinking about the Red Bull Stratos Jump. Sorry, but there is just tons of great physics here. Next question - how big of a balloon would you need to get up to 120,000 feet? I am not going into the buoyancy details of Archimedes Principle - I think that was covered fairly thoroughly with the MythBusters floating lead balloon. However, in short, here is a force diagram for a floating balloon. For a floating balloon, the buoyancy force must equal the weight of the whole thing. It turns out that the buoyant force is equal to the weight of the gas (or fluid) the object displaces…