acceleration

Tom and Jerry, or Fetch! with Ruff Ruffman? Answer: Tom and Jerry. What? Yes. The reason: Tom and Jerry has bad physics but does not pretend like it has good physics. I know this is probably going to "type-cast" me as "that guy that keeps attacking Ruff Ruffman." Soon to be followed by "Leave Ruff ALONE!" I am sorry, I can't help it. Here is my problem. If you are going be a show, do whatever you like (I might still make some comments). If you are going to be a show that attempts to teach some stuff, don't you think you should get it correct or at least not reinforce bad ideas? The…
Dan Meyer made this awesome photo. He posted it so that others could look at it and come up with lesson ideas to use with this. There are some very good suggestions in his comments. I wasn't going to analyze this because I didn't want to rob some students of the opportunity, but I can't resist. Also, I doubt the first step a student would use would be to google for the answer. HA! I just caught you, you googling student. Ok - I will try not to post any data. However, I will post some info on how I analyzed this. The photo is a composite image from a video clip of a person throwing a…
I have always wanted to ask a question like this - but never found the right test for it. Perfect for a blog. Question: Suppose you are in your car at a stop light behind a truck. The truck is pulling a trailer with a rollable tractor on it. When the light turns green, the truck starts to accelerate. However, the cable holding the tractor to the trailer breaks and the tractor starts to roll off the trailer. You are right behind the trailer. What do you do? Do you have an answer yet? You should probably come up with one quickly. That tractor is rolling off now. I will put the answer…
Better technology sometimes causes problems. In this case, technology has made video cameras really small. Small? That's a problem? Well, the problem (as I discussed previously) is that small cameras are not stable and make "shaky" videos. Well, then increase the mass of the camera - simple. I wanted to test this idea and make a test video with and without extra mass on the camera. I was thinking - what could I attach to it? A 2 lb or 5 lb scuba weight came to my mind. Then it hit me: a water bottle. When do people use these little video cameras? To film their kids or something? If…
First, I think we should all be using smaller lighter cars. They get better gas mileage, they are better for the environment and maybe even reduce traffic? (ok, not sure about that last one - but it is possible). In Buzz Out Loud 918, they were discussing Toyota working on new car bodies built from sea-weed based plastics (from a wired article). One point that was brought is the comparison between old plastic bodies (the pontiac fiero comes to my mind) and these new plastics that should be much stronger. Well, here is the problem. Light strong bodied cars can be dangerous. Really? Yes…
Basically, the title says it all. Here is a short tutorial on projectile motion calculations with a spreadsheet. Record your screencast online I left out a lot of details, so maybe these links will help: Spreadsheet tutorial for numerical calculations (video) More details on numerical calculations Projectile motion
A couple of commenters expressed concern over the use of centrifugal force after my rant on the use of the word force. So, what is the deal with these two terms? Are they ok to use? Are they real forces? First, are they real forces? It depends on what you mean by real. What is a force? Here is a quick overview of what a force is. I previously talked about real vs. non-real forces. For me, I say that if the force is essentially one of the 4 fundamental forces then it is "real". With this definition, centripetal force would be real and centrifugal not real. Centripetal Force Centripetal…
People say I am picky. Ok, sometimes I am. But somebody has to stand up for what is right and just. Maybe I am that person. Please stop using the word force if you don't know what it is. There. I said it. You can attack me now. It wasn't just one thing that got me fired up. It was two things. First, I read this article on physics and football (Physics of 'The Hit' from the NY Times). If it was just this article, I would have let it go and moved on. But no. One of my kids just happened to be watching MythBusters (We all love MythBusters) and there was a discussion that used the term…
I enjoyed the super bowl commercials for the most part. You have to be careful not to have too high of expectations, or you will set yourself up for a big letdown. Here is a quick analysis of one of the commercials. This is a Bud Light commercial where at the end they throw a guy out of an office window because he suggests they save money by not buying beer. Are there any actual office meetings that serve beer? (Sorry if I spoiled the ending for you) I am going to analyze the motion of the guy going out the window. Just because. At some point in the future, I am going to make a short…
I really didn't want to post this, but I am going to anyway. I used ScreenToaster.com to make a screen capture movie (with audio) of a tutorial on spreadsheets. This should accompany my previous post on numerical calculations. Free online screen recorder
We have all seen the Kobe Bryant video of him jumping over an Aston Martin - this keeps coming up on the Internet. There has been vast discussions of whether this is real or fake. I will do my best to examine the evidence. In short (in case you don't want to read the whole thing) Kobe can most likely really jump that high, it is possible that there was some perspective trickery involved. Here is the video in case you are brand new to the WWW: Oh - don't forget I already analyzed Kobe Bryant jumping over a pool of snakes. I voted that was real. First, let me give a personal note to Kobe and…
So, here is a video (from break.com - so you know it is likely fake). null - Watch more free videos If for some reason, you can not view this video, here is the plot. Guy wears parachute and brings a portable thing like a see-saw. Guy approaches large crane dropping a large mass repeatedly (I assume to flatten a dirt road) Guy sneaks up an puts the see-saw under the area that the mass drops on and then stands on the other end of the see-saw. Mass drops, guy shoots up and parachutes down. So, why is it fake? I think the best thing is to give an analysis of the see-saw. To start this analysis…
I saw this video posted on Physics and Physicists: It reminded me that I had at one point tried to analyze this. I had actually posted something about this on the first generation of my blog (which no longer exists). I have found the analysis, and here it is from the archives. Thanks ZZ for reminding me. Could this be true, or is it fake? I started to do an analysis of the trajectory, but I found the following frames: Look at the guy's back. His back starts moving before the water bottle rockets. It must be some type of cable pulling him. If the rockets were propelling him, the rockets…
I finally saw the movie Iron Man. It was good. I feel that I am qualified to evaluate the movie. When I was in high school, I was totally into comic books. Mostly Spider-man, but I still have a significant collection of Iron Man comics. Ok, now you know I am not an Iron Man attacker. I will now attack the movie. Sorry, it's what I do (remember, I already said I liked it). There are several things I could comment on, in fact I recall some other blog talking about the physics of Iron Man. My attack will center on the scene where Tony Stark (Iron Man) escapes from captivity with his home…
Just to be clear, Newton probably didn't have a portable video camera. I do. I have one of these Flip Mino pocket cameras. Very nice. You can put it in your pocket. However, there is a problem with cameras like these (think of video from camera phones). The problem is the mass, it is too small. Video from a camera phone or small portable camera looks too jerky (unless you are careful). Sometimes it is jerky to the point that it makes me feel barfy. The reason this happens is that with a small mass, a force can cause a significant acceleration. Let me draw a picture (you know I like…
College 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 "…
Clearly, 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 the…
Pre Reqs: momentum principle, forces,energy, vectors Really, there is not much new here. This is an introduction to objects that interact. To describe this, I will need to pull several different ideas together (that you have probably already looked at). Let me start with a simple case. Suppose I have two objects, maybe they are two asteroids in space. I will call them asteroid A and B: In this situation, the two objects have different momentums but one interaction between them. Notice that the gravitational force on asteroid A is the same magnitude but opposite direction as the force…
You see this all the time in textbooks: This is often described as "the acceleration due to gravity". Is this really the best thing to call this? No. A better name would be "the local gravitational field" and list it in units of: Where does g come from? The usual source is from the weight, or gravitational force: This is the best way to write it (in vector notation) but you will often see it written as: which looses the vector nature. In the vector notion, the vector g is a vector pointing towards the center of the Earth. Why not acceleration due to gravity? Take the following case…
This 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…