python
rallain | May 12, 2009Maybe you have seen this trick. Basically, you hold by supporting it with two fingers from the bottom. You then move your hand around to keep it balanced while the stick is vertical. It is really not as hard as it looks. Also, there are two things that can make your job easier. Use a longer stick, or add an extra mass at the end of the stick. Here is a video of me demonstrating this. (I forgot, this also an event in the show Unbeatable Banzuke)
Balancing a Stick Demo from Rhett Allain on Vimeo.
So, how does this work? Let me start with a stick that is mostly vertical and supported by…
rallain | December 29, 2008In part I of this post, I talked about the basics of projectile motion with no air resistance. Also in that post, I showed that (without air resistance) the angle to throw a ball for maximum range is 45 degrees. When throwing a football, there is some air resistance this means that 45 degree is not necessarily the angle for the greatest range. Well, can't I just do the same thing as before? It turns out that it is a significantly different problem when air resistance is added. Without air resistance, the acceleration was constant. Not so now, my friend.
The problem is that air…
rallain | December 26, 2008College football season is coming to an end (I guess technically, the season is over - it is bowl season). Anyway, this is something I wanted to do a long time ago, but I kept getting side tracked. If I don't do it now, I will never do it. Most people know that a ball without air resistance (traditional projectile motion) goes the farthest if you throw it at a 45 degree angle. What if there is air resistance? Why is 45 the best angle without air resistance? What other questions are there?
I posted about projectile motion before - so you might want to start there. When people say "…
rallain | October 21, 2008[In a previous post, I talked about numerical calculations](http://scienceblogs.com/dotphysics/2008/10/basics-numerical-calculation…). The basic idea is to use the momentum principle and the following "recipe":
Update the position of the particle
Update the momentum of the particle
Update the force on the particle
Looks great, right? Well, it mostly is great. I want to give a couple of pointers about the last step, update the force on the particle. How and when can you do this? Really, in numerical calculations, you will see two types of forces:
Forces that you can calculate: That looks…
rallain | October 16, 2008Maybe you know I like numerical calculations, well I do. I think they are swell. [VPython](http://vpython.org) is my tool of choice. In the post [Basics: Numerical Calculations](http://scienceblogs.com/dotphysics/2008/10/basics-numerical-calculation…) I used vpython and excel to do something simple. I will do that again today (in that this problem could also be solved analytically). However, there is one big difference. This problem has a non-constant forces. Suppose I have a mass that is connected by a spring to a wall. This mass-spring is sitting on a table with no friction.
, [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 23, 2008In my classes, I like to bring up the question:
*Why do astronauts float around in space?*
The most common response to this question is that they float around because there is no gravity in space. Some people take this a small step further and say that there is no gravity in space because there is no air in space. This is why they claim there is no gravity on the moon (even though there is - more on this later).
I like to start off with the concept of gravity. Gravity is an attractive force between any two objects with mass. Your pencil and your dog both have mass so there is a force pulling…