acceleration

One of my favorite podcasts to listen to while driving or mowing the lawn is [Buzz Out Loud](http://bol.cnet.com). Buzz Out Loud (BOL) is basically just a tech-based podcast, but very entertaining. Anyway, as part of my attention seeking disorder, I try to get mentioned on the show. I succeeded once when I posted my [Optimal Commuting Speed Calculator](http://www.dotphys.net/page1/page10/efficiency/calculator.html). When I heard Tom and Rafe talking about orbital speeds, I realized this was my chance. Find any tiny flaw in their reasoning and I could perhaps come up with a comment worthy…
Big trucks are not as popular as they used to be, but gas prices are going down so maybe this commercial for the ford F-150 will start showing up again: They say its a real demonstration, but it has seemed odd to me. (they also say this is a professional driver on a closed course and don't try this at home - damn! I was SO going to do that this weekend). Here is my analysis: Here is the important data I have gathered from the Internets. The truck (a Ford F-150) stops a plane C-123 Provider The curb weight of the F-150 is around 5,000 lbs - depending on options and stuff. The empty weight of…
Atwood's machine is the name of a device that looks like this: Also known as "two masses on a pulley". Surprisingly, this simple device comes up a lot in intro physics texts. It also brings up some interesting issues. I will go over the basic way to solve a problem like this (as an example) and then talk about the other interesting issues it brings up. Problem: A small, low mass, pulley has a light string over it connected to two masses, m1 and m2. If released from rest, what is the acceleration of the two masses. Where to start? This is actually a very difficult question for…
Here is a video of a guy jumping 35 feet into a pool of water only 1 foot deep. UPDATE: Apparently, that video went away. Here is another version. How does this work? I don't think I even need to do a video analysis of this motion, all the important info is given. I will assume that air resistance did not play a signficant role (and that is a good assumption - or good enough - see this for example: motion of a falling tennis ball). So, here is the situation. Part 1: guy falls 35 feet 5 inches (10.8 meters). ![Screenshot 16sd](http://scienceblogs.com/dotphysics/wp-content/uploads/2008/11/…
On MythBusters this week, Adam and Jamie tested the bullet-proofness of various objects. The one that sticks in my mind is the ipod. The said there was a report of a solider being shot by an AK-47, but he was saved because the bullet hit his ipod. To test this, Adam shot an AK-47 at an ipod and it went through. Their conclusion was that he was also wearing body armor. I am not sure I like that conclusion. Why would someone report that the ipod saved him if he was also wearing body armor? Maybe they would, but not sure. I was thinking, maybe the bullet went through the ipod because they…
Maybe 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. ![…
**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/…
In 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: ![Screenshot 20](http://scienceblogs.com/dotphysics/wp-content/uploads/2008/10/screensho…) Yes, maybe someone would add gravity and the chair pushing up, but this shows the…
Popular 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…
In 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…
**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…
**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: ![data2](http://scienceblogs.com/dotphysics/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://scienceblogs.com/dotphysics/kinematics_data.…
Can 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…
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://scienceblogs.com/dotphysics/wp-content/uploads/2008/09/page-6-1…) 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://scienceblogs.com/dotphysics/wp-content/uploads/2008/09/page-6-2…) 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…
There is no air resistance in line rider. Sorry to spoil the suspense. To test for the presence of an air resistance force, a track was created that let the rider fall. ![linerider air 1](http://scienceblogs.com/dotphysics/wp-content/uploads/2008/09/linerider…) (note the markers on the side. These are used to keep track of how the origin is moving). Below is the y position of the rider as a function of time: ![linerider falling](http://scienceblogs.com/dotphysics/wp-content/uploads/2008/09/linerider…) In this situation, the rider falls about 100 meters. A quadratic line is fit to the data…
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://scienceblogs.com/dotphysics/wp-content/uploads/2008/09/line-ride…) 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…
Part I: Introduction http://linerider.com is a flash "game" in which the user can create tracks. A rider is then allowed to slide down these tracks. If you have not played this, I recommend you DON'T play it. It is very addicting and can consume many hours of your time (hours you would otherwise spend on Digg or surfing needlessly). In this short report, I will analyze the physics involved in line rider. An obvious question is "why not just ask the line rider programmer?". Well, that would not be too much fun. Would it? So, there is the first reason - its fun. The second reason is to give an…
**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: ![s kinematics](http://scienceblogs.com/dotphysics/wp-content/uploads/2008/09/s-kinemat…) This relates the position (s), the velocity…
**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…
In a comment on my last post, What is Dark Energy, Kendall asks the following, which is such a good one I think it deserves its own post: I thought the expansion was accelerating? Aren’t you saying that it is on its way down to 85% of its current rate? Sounds like expansion is slowing, but still leaves us with an open universe… People do say the expansion of the Universe is accelerating. But that doesn't mean that the expansion rate is accelerating. It means that if you take a look at any one galaxy that isn't gravitationally bound to us in the Local Group (that is, any big galaxy that isn't…