kinematics
rallain | December 23, 2008Clearly, I am not a professional blogger. I am an amateur. This is because I was under the impression that only amateur bloggers could compete in the blogging olympics. When did they change these rules? Anyway, Adam Weiner did a physics-based analysis of the latest Star Trek movie trailer. Here is the trailer:
In the trailer (oh, spoiler alert) a young Kirk jumps out of a car before it goes over a cliff. It does look odd, and that is why I had intended to analyze it. In Adam's analysis, at PopSci.com the basic approach was:
Take the initial velocity of the car (from the clip)
Assume…
rallain | November 24, 2008This is an old video, but still interesting. In this video clip, Kobe Bryant jumps over a pool of snakes.
You are probably thinking what I thought when I see that - this doesn't look real. Really, it must be fake. Why would Kobe jump over a pool of snakes? Isn't that dangerous (even if there were no snakes in there he could hurt himself). Video analysis is needed. Is this fake or is it real?
Start with my favorite video analysis tool (tracker). Use this to get position time data.
Step 1: Get the movie. I used Mpeg Streamclip to get the movie in quicktime format from the flash video…
rallain | November 20, 2008Georgia Tech is playing Miami (not the real Miami, the other one Miami Florida). Right after a commercial, the camera shows this sign from a student (or just person) at the game:
(Sorry if the image isn't that great.) I had to pause the game and take a closer look at this sign. I am not sure I get it. In case you can't see, the sign shows two players and the trajectory of a ball (clearly labeled x and y axes). The equations are:
. The basic idea is to use a couple of different "machine" parts to build something that will move an object into a target area. Not a bad game. But what do I do when I look at a game? I think - hey! I wonder what kind of physics this "world" uses. This is very similar to [my analysis of the game Line Rider](http://scienceblogs.com/dotphysics/2008/09/the-physics-of-linerider/) except completely different.
Fantastic Contraption gives the unique opportunity to build whatever you want. This…
rallain | October 14, 2008**Pre Reqs:** [Kinematics](http://scienceblogs.com/dotphysics/2008/09/basics-kinematics.php), [Momentum Principle](http://scienceblogs.com/dotphysics/2008/10/basics-forces-and-the-moment…)
What are "numerical calculations"? Why are they in the "basics"? I will give you really brief answer and then a more detailed answer. Numerical calculations (also called many other things - like computational physics) takes a problem and breaks into a WHOLE bunch of smaller easier problems. This is great for computers ([or a whole bunch of 8th graders](http://scienceblogs.com/dotphysics/2008/09/…
rallain | September 25, 2008In a [previous post](/dotphysics/2008/09/basics-making-graphs-with-kinematics-stuff-part-ii/), I talked about how to plot kinematics data with a spread sheet and how to fit a quadratic function to the data. In the back of my head I remember "Don't trust Excel". I seem to recall someone claiming that Excel did not do a proper fit. To test this, I collected some data and used several methods to fit the data:
MS Excel's built in function fitting
Using the spread sheet (Excel) to manually calculate the best fit parameters
Vernier's Logger Pro (version 3.6.1)
Plot 0.997 - http://plot.micw.eu…
rallain | September 21, 2008**pre-reqs**: [kinematics](http://scienceblogs.com/dotphysics/2008/09/basics-kinematics.php) *I don't think you need [part I of this](http://scienceblogs.com/dotphysics/2008/09/basics-making-graphs-with-ki…) if you don't want*
So, you still want to make a graph with that kinematics data? You think that graphs on paper are too barbaric? Well, if you are ready, you can use a spreadsheet. But be careful. If you don't know what you are doing, you can cause some damage (much like flying a 747 after reading a blog about it). Spreadsheets allow you to do a couple of things.
make pretty graphs…
rallain | September 18, 2008**pre reqs:** [kinematics](http://scienceblogs.com/dotphysics/2008/09/basics-kinematics.php)
Suppose there is some experiment in which you throw a ball up and collect position and time data (with video analysis). What do you do with this data? Your instructor told you to make a graph, but how do you do that?
Here is the fictional data you (or I) collected:
Here is the text file with the data if you want to reproduce the graphs I make here [kinematics data](http://scienceblogs.com/dotphysics/kinematics_data.…
rallain | September 14, 2008Can you believe it? Have you seen this video?
Are you thinking what I am thinking? WOW. How could these people not follow my rules for cool internet video. Once again, here they are:
1Keep the camera stationary. This way I don't have to keep moving the origin in the movie.
2Don't Zoom. Same reason, this video followed that rule.
3Include a clear and obvious calibration object. A meter stick would work, or even a Kobe Bryant (I can look up his height). Maybe it could be a Ford F-150 that has a known length. Something!
4Include the mass and height of all people involved.
5Use high…
rallain | September 14, 2008Friction in Line Rider
Is there friction in Line Rider? Does it function as physics would expect? To test this, I set up a simple track:
Basically, a slope with a flat part to start with and to end with. Let me show you something simple before further analysis:
This is the x-position vs. time for the line rider on the first horizontal portion of the track (before he or she goes down the incline). This shows the rider…
rallain | September 13, 2008Scale of the Line Rider
First, we assume that the line rider is on Earth and for low speeds will have a free-falling acceleration of 9.8 m/s2. Next, an arbitrary distance is selected. In this case the length of the sled is chosen to be 1 LU (Linerider Unit).
The goal will be to put the linerider in a free fall (where air resistance should be able to be ignored) and determine his (it could be a she, it is difficult to tell) acceleration in LU/s2. Then we can determine the conversion factor from LU/s2 to…
rallain | September 6, 2008Here is the video in question:
Looks too incredible to be real for me. That is when I start to question things. Is this fake or not? To answer this, I took a clip that showed a person launching a grocery item over the isle. This was a good shot to look at because it was *mostly* perpendicular to the camera view. I then used [Tracker video analysis (free) tool](http://www.cabrillo.edu/~dbrown/tracker/) to get x-y-time data for the flying projectile grocery. The scale was difficult, so I just guessed that the guy on the left was 5 foot 10 inches. Here is the vertical position data for…
rallain | September 5, 2008**pre-reqs:** [kinematics](http://scienceblogs.com/dotphysics/2008/09/basics-kinematics.php)
My previous "basics" post was on kinematics (in one dimension). But what about two dimensions? In particular, what about projectile motion. My motivation here is that I was about to talk about analysis of a video that involved projectile motion and I don't want to go over all the stuff again and again.
Let me start with a generic, one-dimensional kinematic equation:
This relates the position (s), the velocity…
rallain | September 3, 2008**pre reqs:** *none*
Often I will do some type of analysis that I think is quite cool. But there is a problem. I keep having to make a choice. Either go into all the little details, or skip over them. My goal for this blog is to make each post such that someone could learn some physics, but I also don't want it to go too long. So, instead of continually describing different aspects of basic physics - I will just do it once. Then, when there is a future post using those ideas, I can just refer to this post. Get it?
Fine. On with the first idea - kinematics. Kinematics typically means…
rallain | August 27, 2008Clearly the MythBusters did this before I did (it's just airing tonight though). I just wanted to say that I posted some videos of the Apollo "jump salute" video analysis and also sped it up to "Earth-like" accelerations. I then made a video of my daughter doing the same thing on Earth and slowed it down. Yes, the MythBusters did it better, but I just wanted to say "me too". My analysis is here:
[Undoing Fake Moon Landing Videos](http://www.dotphys.net/files/moon-time.html)
P.S. I also slowed down a video of Kobe Bryant Jumping so he has an acceleration of that on the moon.