velocity
esiegel | December 11, 2013"Where you used to be, there is a hole in the world, which I find myself constantly walking around in the daytime, and falling in at night. I miss you like hell." -Edna St. Vincent Millay
It was just a little while ago that we were all speculating wildly -- and optimistically -- about Comet ISON, as it plunged towards the Sun from its origins in the very, very distant Solar System. As its perihelion date (the moment of closest approach to the Sun) drew near, you may have noticed something interesting about photos of the comet: it's tail appeared to get longer and longer!
Image credit &…
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 | 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 | 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 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 10, 2010In the last episode of MythBusters, they wanted to see if a tornado could make some glass cut off a person's head. The first attempt was just to take some glass and through it at a simulated human neck. Clearly, this wasn't quite the same as a tornado.
So, here was their plan. If they want to simulate glass moving at 300 mph, they could get a bigger piece of glass and put it on a truck moving at 80 mph. The result would give a piece of glass with the same kinetic energy as a smaller piece moving at 300 mph. Their calculations look to be correct. However, the question is: would this make…
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 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 24, 2010While I am still fresh on the Space Jump topic, let me take it to the extreme. Star Trek extreme.
SPOILER ALERT
But really, is this a spoiler alert if it is from the trailer of a movie that has been out forever? Of course, I talking about the latest Star Trek movie where three guys jump out of a shuttle and into the atmosphere.
So, in light of the Red Bull Stratos jump, how would this jump compare? First, my assumptions:
This Star Trek jump is on the planet Vulcan. I am going to assume this is just like Earth in terms of gravity and density of air.
The jumpers in Star Trek have on stuff…
rallain | April 9, 2010So, I complained about MythBuster's explanation of relative velocity. How would I explain this? I would start by saying that velocity is relative. Here is the definition for velocity:
I put the "avg" in there because it is more true. If the acceleration is zero, I could drop this. For the rest of this post, I am going to assume zero acceleration. Ok. But what is the r vector? It is simply a vector from the origin to the object. Here is a picture.
Simple, right? And so the velocity tells how this vector r changes. But wait. Who says that I used the correct origin? How do you…
rallain | February 22, 2010My last Olympics post may have been a little complicated. I am going to try to make this one a little easier. In this post, I want to look at the landing portion of a ski jump. This could apply to THE ski jump, but there are some things in that even that make it a little more complicated (but I might come back to that in another post). For this case, I will consider the freestyle event - aerials. I didn't search too long, but here is a nice short video.
First, a quick estimation of how high they are "falling" from on the way down. In that video, the jumper takes about 1.5 seconds to get…
rallain | January 31, 2010This is really random, but quick. I was channel surfing and saw the end of the movie: Fantastic 4 - Rise of the Silver Surfer. SPOILER: At the end someone really big explodes in space. There, that wasn't too much of a spoiler, was it? (unless you read the title)
I know I am a loser. I initially thought: wow, that seemed pretty fast for that scale. I wonder if that exploding stuff was going faster than the speed of light. OH! I know, I will use Tracker to measure it. It is video that is set for analysis since it has the Earth in there - and I am pretty sure I know how big that is.…
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…
rallain | January 14, 2010If you know me, you know I love Tracker Video Analysis. Basically, it is a free-java program that allows you to get position-time data of a moving object from a video. In Tracker version 3.10, there is now the autotracker feature. This will automagically mark the location of an object moving in a video. How do you use it?
First, the video. This is a video I made of a plane landing at an airport. Not much exciting going on, but that never stopped me before. I put this video on vimeo instead of youtube because vimeo allows you to download the original video.
Landing Airliner from Rhett…
rallain | December 18, 2009Fight Science is an entertaining show. Great graphics. The basic idea is to look at the science in different fighting styles. They had a clip-style commercial on it during a MythBusters episode I was watching. And from that, I can say that the kicking looked cool, but the science needs some work.
The Setup
The basic idea is that they wanted to compare kicks from different fighting styles. From what I can gather, they collected data by having some dudes kick this "kicking bag". During the kick, they measured the force exerted on the bag and they had a sensor on the kicker's leg - I…
rallain | September 30, 2009This is really a lab that I have students do, but I am pretty sure they don't read this blog - so it is ok. If they are reading this, hi!
We have these projectile cannons that shoot small balls. In order to look at projectile motion, they need to first determine the launch speed of the ball. I have a great method for this. Basically, shoot the ball horizontally off the table and measure how far horizontally it goes. You can get the final location of the ball by having it hit a piece of carbon paper on top of normal paper. If you don't know what carbon paper is, you are young.
Anyway,…
rallain | September 28, 2009I think we are entering a new era. An era where it is quite simple to find and get great videos. Oh, just saw a great tackle on the TV? In the old days, you would have to get that video off the TV yourself. Not anymore. Welcome to the interwebs. Also, the quality is awesome compared to 10 years ago. Here is the video. Yes, I know this is from several weeks ago - I am slow. Also, thanks to the person that put this on youtube - I edited your clip to remove the music and just look at the one collision. You did a good job though.
In terms of video analysis, this isn't too bad of a video…
rallain | August 23, 2009I saw this video on digg or reddit. I can't remember which.
I was in awe. Then I started thinking. I wonder how fast that water was moving up right after the explosion. Too bad the video doesn't have a scale. Well, it kind of does - there is that ship. I am terrible at ship identification though. Maybe I can use my favorite scaling trick - assume the stuff is on the surface of the Earth. This means that free falling objects would have an acceleration of -9.8 m/s2. Let me try this on the water as it falls. Oh, trust me. I know it is not really free falling, but it is in this big…
rallain | August 21, 2009Forgive me if I don't know the official parkour term for this move. This is where you have two walls that are close to each other and you vertically climb them. Here is a shot of Mark Witmer (from Ninja Warrior) doing the wall climb.
Doesn't look too hard, does it? Well, I think it depends on how far apart the two walls are. This is actually one parkour move that my kids like to do (Hey kids! Don't do that! Let me get my camera though because this will be perfect for my blog)
I am going to start with this second kind of wall climb. Simply because it is easier due to symmetry. So,…
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…