rallain | October 9, 2008Dear High School students,
How are you? I am fine. I am very glad that I am no longer in high school. Maybe you enjoy high school, but for me, it was not so good. Don't get me wrong, I went to an excellent high school (Waubonsie Valley HS). There was something in high school that didn't feel right. Maybe it was being in classes for too long and the lack of time to work on my own projects. Maybe it was lack of freedom in choosing my own classes (there was some freedom to chose). Or perhaps I was just not mature enough to enjoy it. Needless to say, I am past that now.
I think now, how…
rallain | October 7, 2008In this post, I am going to talk about real and not real forces as well as the fake centrifugal force (if you don't like the word "fake" you could replace that with "fictitious")
First, an example: suppose you are in a car at rest and press the gas pedal all the way down causing the car to accelerate. What does this feel like? If I weren't skilled in the art of physics, I might draw a diagram something like this:
Yes, maybe someone would add gravity and the chair pushing up, but this shows the…
rallain | October 6, 2008Question from class: *What do magnets interact with?*
Basically, everyone said "metals". I am quite surprised. No one specifically indicated that magnets only interact with iron and steel (of the materials they would likely see). I understand that steel is a very common material they are likely to encounter, but what about aluminum? I think this points to the idea that very few of my students have actually played with magnets. This is a shame. Everyone loves magnets.
So, I propose you go out and give someone you love some magnets today.
rallain | October 6, 2008Popular demand (from a few people - you know who you are) requested another level for the force game. I am open to naming this game. Ideas for levels have been suggested also. There is a new rule change. You must be stopped (or almost stopped) in the red circle.
Learn more about this project
Update:
I guess I didn't include instructions on how to play the game. Just click on the applet window to make sure it is active. Press the space bar to start the game. Once the game starts the objective is to use rocket thrusters (the arrow keys) to move the rocket (the black rectangle) into the…
rallain | October 6, 2008**Pre reqs:** [Free body diagrams](http://scienceblogs.com/dotphysics/2008/09/basics-free-body-diagrams.php)
Friction is an interaction between two objects in contact that opposes relative motion of those two objects. It is not something fundamental (like gravity, or electromagnetic force), but it comes up enough that it will be worthwhile to talk about it. Let me start with a simple example. Suppose I have a book on a table. Here is the free body diagram for the book:
Simple enough - right? There…
rallain | October 6, 2008I already said I like [scratch from MIT](http://scratch.mit.edu). After building a simple rocket model, the kids said it should be a game. I caved. Here it is:
Learn more about this project
To play, press the space bar. The arrow keys are rocket thrusts. The goal is to get to the red circle in as little time. If you hit the wall or the sides, you start back at the green circle. Please forgive me masters of scratch (I know who you are - you find something to complain about in my program).
rallain | October 4, 2008Magic tricks are cool. Especially when the trick is really physics. In this trick, I can make one of the four balls move more than the others. (When you watch the video, you will see why I am not a professional magician). You could set this up in a variety of ways. I state that if we (me and people around me) all work together with our mind and focus on the same ball, our brain waves can resonate with that ball and make it move. I let the people around me pick. In this video, I make the smallest two move.
So, what is the trick? The trick is not a trick. It is not resonance with brain…
rallain | October 4, 2008I think it is time for me to talk about energy. My ultimate goal is to give some insight into the many stories about perpetual motion. To do this, I will first talk about the fundamentals of energy.
**What is Energy**
I started thinking about this, and at first I realized that I did not have a good, short explanation of energy. The most commonly used definition in science text books is:
*Energy: the ability to do work (or something dreadfully vague like this).*
But what is work? It may be no surprise to find that many college level physics texts avoid defining energy. After some serious…
rallain | October 2, 2008Gas prices may be trending down, but they are still quite high. How can we save gas? One of my colleagues suggested we can save gas by getting rid of all drive throughs. This means it is my job to estimate how much could be saved.
**Starting Assumptions (estimations)**
How many drive-throughs are there in the U.S.A.? When I think of drive-throughs, I think of McDonalds. [Wikipedia](http://en.wikipedia.org/wiki/Mcdonalds) says there are 31,000 restaurants world wide. I am going to say there are around 20,000 in the U.S. that have drive-throughs. So then, how many total drive-throughs?…
rallain | October 2, 2008I was recently re-watching a MythBusters episode and I found something I had wanted to explore previously (but accidentally deleted the episode). Here is a short clip from the "shooting fish in a barrel" episode:
Did you see what I found interesting? That big barrel of water left the floor from being hit by a bullet.
The question here is: Does a bullet have enough energy to increase the gravitational potential energy of the barrel to that height?
First, let me gather some data. From the episode, the Mythbusters were firing a 9mm pistol round into the barrel. I don't know much about…
rallain | October 1, 2008I actually have some important things to do. However, I thought I would make another scratch program. Yes, this will all lead to something useful (that is what I told my wife). Anyway, in this program, I made a spaceship with 4 thrusters. The great thing about this is it show what forces do to the motion of an object. I already had a suggestion to make it into a game with a score.
Learn more about this project
Use the arrow keys to turn on the 4 thrusters.
rallain | October 1, 2008I can't remember how I found this, but [Scratch](http://scratch.mit.edu) is a graphical programming language developed at MIT. My kids love this. In order to make sure they don't know more than I do, I created my own scratch program. I am sure someone from the scratch community will attack it for some reason, but I am ok with that.
The program shows a numerical calculation of the motion of a box with a constant force on it. You change the mass and the force. It "sort of" plots the position as a function of time. Don't worry python, I still think you are the best.
Learn more about…
rallain | September 30, 2008Which wastes more fuel? (and thus produces more carbon dioxide). This is a difficult to question to answer for a variety of reasons. The main reason is that a speed change from 71 mph to 70 mph is different than a reduction from 56 to 55 mph.
First, let me be clear that the question of how much fuel is wasted using daytime running lights (or DRL as they are called) has already been addressed. The first source I found was howstuffworks.com
**Assumptions**
The daytime running lights on a car run at about 100 watts (for the pair)
The energy density of gasoline is 1.21 x 108 Joules/gallon.
A car…
rallain | September 30, 2008So, we have some new faculty. New to the university, and new to teaching. What advise can I offer? Here are few things to consider:
Never show fear. Students can sense fear. They see it as a sign of weakness. They may attack. If you are afraid, act like you are not.
When in doubt, imitate. Don't try to reinvent anything. Don't try to find your own style, that will come with time. The goal is to become familiar with teaching and to become familiar with the content. Once you do that, you will have a better idea about how YOU want to run things. So, in the mean time, find an…
rallain | September 30, 2008**Pre Reqs:** [Intro to Forces](http://scienceblogs.com/dotphysics/2008/09/basics-what-is-a-force.php), [Vectors](http://scienceblogs.com/dotphysics/2008/09/basics-vectors-and-vector-ad…)
Hopefully now you have an idea of what a force is and what it isn't. What do you do with them? The useful thing to do with forces is to determine the total force acting on an object. At the beginning of the introductory physics course, you will likely look at cases where the total force is the zero vector. This is called equilibrium. Even if you are looking at cases where the forces don't add up to the…
rallain | September 28, 2008When mowing the lawn, I like to listen to podcasts. One of my favorites is [Buzz Out Loud](http://bol.cnet.com). This weekend, I was listening to episode 817 and one of the topics of discussion was MySpace and their DRM free music stuff. [Wired](http://blog.wired.com/music/2008/09/myspace-launche.html) had a description of what they were going to do. That is not my point. The point is the claim that you could make an infinite number of playlists. How about I calculate (or estimate) the number of different playlists one could make.
First, the idea behind the idea. Calculating the number…
rallain | September 26, 2008On a previous episode of The MythBusters, Adam and Jamie made a lead balloon float. I was impressed. Anyway, I decided to give a more detailed explanation on how this happens. Using the thickness of foil they had, what is the smallest balloon that would float? If the one they created were filled all the way, how much could it lift?
First, how does stuff float at all? There are many levels that this question could be answered. I could start with the nature of pressure, but maybe I will save that for another day. So, let me start with pressure. The reason a balloon floats is because the air…
rallain | September 26, 2008**Pre-reqs:** None.
I intend to talk about forces and force diagrams, but there is a more fundamental question to address first. What is a force? Most texts define it as a push or a pull. That really isn't a bad definition. Maybe a better (or maybe worse) definition would be "forces are things that change the motion of an object" (change being the key word). If I had to choose one definition of force, it would be something like this:
**Force:** *A force is an interaction between two objects. There are 4 known forces:*
Gravitational force: An attractive long range force between objects…
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 24, 2008**pre reqs:** [Vectors and Vector Addition](http://scienceblogs.com/dotphysics/2008/09/basics-vectors-and-vector-ad…)
This was sent in as a request. I try to please, so here it is. The topic is something that comes up in introductory physics - although I am not sure why. There are many more important things to worry about. Let me start with an example. Suppose you are on a train that is moving 10 m/s to the right and you throw a ball at 5 m/s to the right. How fast would someone on the ground see this ball? You can likely come up with an answer of 15 m/s - that wasn't so hard right?…