Tag kinematics

Physics of Fantastic Contraption I

rhettallain 1 Comment

One of my students showed me this game, [Fantastic Contraption](http://fantasticcontraption.com/). 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://blog.dotphys.net/2008/09/the-physics-of-linerider/) except completely different.

Fantastic Contraption gives the unique opportunity to build whatever you want. This is great for creating “experiments” in this world.

The first step is to “measure” some stuff. The game includes three types of “balls” and two types of connectors. The balls are:

  • Clockwise rotating
  • Counterclockwise rotating
  • Non-driven

Connectors:

  • wood lines – these can not pass through each other
  • water lines – these can pass through each other, but not the ground

First question: Do the different balls have the same mass? This can be tested by creating a little “balance”

![Screenshot 05](http://blog.dotphys.net/wp-content/uploads/2008/10/screenshot-052.jpg)

Continue reading “Physics of Fantastic Contraption I” →

Comparison of quadratic curve fitting

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In a [previous post](http://blog.dotphys.net/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/ – a program derived from Sci-Plot

I already discussed how to add a quadratic fit in Excel using the built in tools. Perhaps later I will also discuss Logger Pro and Plot. But how do you come up with a function to fit data? The basic idea is to create a quadratic function and vary the parameters such that the deviation of the actual data from the function is minimized. That is much detail as I want to go into except for the following two links that I used:

Continue reading “Comparison of quadratic curve fitting” →

Basics: Making graphs with kinematics stuff part II

rhettallain 6 Comments

**pre-reqs**: [kinematics](http://blog.dotphys.net/2008/09/basics-kinematics/) *I don’t think you need [part I of this](http://blog.dotphys.net/2008/09/basics-making-graphs-with-kinematics-stuff/) 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). Speadsheets allow you to do a couple of things.

  • make pretty graphs
  • fit mathematical functions to data

Of course they actually do much more – but you need [“clippy”](http://en.wikipedia.org/wiki/Clippy) to help you with that.

First, what software do you use? I think most people will immediately go for Microsoft Excel. I have to admit, this is what I use because I am so familiar with it. Many people already have this also. Truthfully, it is a good spreadsheet program (but not perfect). There are some free alternatives:

  • Open Office – I use the Mac OS X variant Neo Office
  • Online spreadsheet like Zoho) or Google Docs. Both of these are fairly useable.
  • Other – like Apple’s spreadsheet or other non-free stuff.
  • A final excellent option is Vernier’s Logger Pro. Although it is not free (nor perfect) it is not too expensive and can be covered by a school site license

For this tutorial, I will show explicitly how to make graphs using MS Excel. I was going to use open office, but in order to fit a polynomial to data, you have to do some more serious stuff. The basic idea is the same no matter what you use.

Continue reading “Basics: Making graphs with kinematics stuff part II” →

Basics: Making graphs with kinematics stuff

rhettallain 4 Comments

**pre reqs:** [kinematics](http://blog.dotphys.net/2008/09/basics-kinematics/)

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:

![data2](http://blog.dotphys.net/wp-content/uploads/2008/09/data2.jpg)

Here is the text file with the data if you want to reproduce the graphs I make here [kinematics data](http://blog.dotphys.net/kinematics_data.txt)

Continue reading “Basics: Making graphs with kinematics stuff” →

Physics of Linerider IV: Friction?

rhettallain 1 Comment

Friction 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:

![Page 6 1](http://blog.dotphys.net/wp-content/uploads/2008/09/page-6-1.jpg)

Basically, a slope with a flat part to start with and to end with. Let me show you something simple before further analysis:

![Page 6 2](http://blog.dotphys.net/wp-content/uploads/2008/09/page-6-2.jpg)

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 traveling at a constant speed of 0.71 m/s. If friction were present, the rider would slow down. If you do not believe me (and why should you?) try creating your own line rider track with a long horizontal section. The rider will not stop, but continue on at a constant speed.

Ok, so no friction on the horizontal line. This makes a little bit of gaming sense. Who would want a rider to stop in the middle of the track and be stuck? That wouldn’t be fun. But, is there friction on non-horizontal portions? To test this, I will use the work-energy principle.

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Physics of Linerider Part II: Scale

rhettallain 1 Comment

Scale 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).

![line rider](http://blog.dotphys.net/wp-content/uploads/2008/09/line-rider.jpg)

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 m/s2.

Continue reading “Physics of Linerider Part II: Scale” →

Fake or Not: Physics analysis of “Extreme way to shop for groceries”

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Here 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 two tosses.

![grocery](http://blog.dotphys.net/wp-content/uploads/2008/09/grocery.jpg)

A few things to notice:
– The plots are mostly parabolic. This is what you would expect from a real toss (air resistance would be small)
– The two tosses have essentially the same acceleration.
– The acceleration of these two tosses is in the ball park of -9.8 m/s2. Yes, they are not right on, but I totally guessed on the scale of the video.

So, from this, I think that shot is real. It is still incredible. Maybe they did this for like two hours to get it right. Maybe they just got lucky. Maybe they used the force and the force is strong in their family.

I was going to add an analysis of how off they could be on their throws and still make the “basket”, but I got lazy. Sorry. Maybe I will add that later.

Basics: Projectile Motion

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**pre-reqs:** [kinematics](http://blog.dotphys.net/2008/09/basics-kinematics/)

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.

Continue reading “Basics: Projectile Motion” →

Basics: Kinematics

rhettallain 1 Comment

**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 a description of motion (not what causes that motion). In particular, kinematics looks at position, velocity, and acceleration. In this post, I will try to stay in one dimension. This will make things look simpler without really losing too much. Later, when I talk about vectors, I will make it all better.

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Mythbusters Moon Stuff and Me

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Clearly the MythBusters did this before I did (it’s just air 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.