energy
rallain | August 5, 2010This is a classic problem. You are in a car heading straight towards a wall. Should you try to stop or should you try to turn to avoid the wall? Bonus question: what if the wall is not really wide so you don't have to turn 90 degrees?
Assumption: Let me assume that I can use the normal model of friction - that the maximum static friction force is proportional to the normal force. Also, I will assume that the frictional coefficient for stopping is the same as for turning.
Stopping
I am going to start with the case of trying to stop. Suppose the car is moving towards the wall at a speed…
rallain | July 23, 2010Check this out - NY Times: No Motors, but Mistrust at Tour de France.
So, the short story is that some people claim that Cancellara is cheating by putting a hidden electric motor in his bike. Now they are going to do random hidden-motor checks.
I have analyzed this motor-in-a-bike already:
Energy in a hidden battery: The short answer is that you could get about 500 watts for about 1.5 hours with a hidden battery that weighs 1.6 kg. Doable, yes. Advisable? Probably not. Also, you would probably hear the motor being used.
Do bikers cheat? In this post I look at some clips of Cancellara…
drorzel | July 15, 2010In the comments following the silly accelerator poll, onymous wrote:
[T]he point of the LHC isn't to discover the Higgs. No one in their right minds would build a 14 TeV pp collider if their only goal was to discover the Higgs.
While it's true that the ultimate goal of the LHC is to discover more exotic particles that may or may not exist (blah, blah, supersymmetry, blah) most of the hype has focussed on the Higgs, which is the one thing they're pretty sure they'll find (comments later in that thread notwithstanding). This is one of the potential problems with the way the machine has been…
rallain | July 11, 2010My car had a flat tire. When you get a flat tire, you might as well make something useful of it - right? As I was jacking the car up, I had a great idea. Use this for one of my "Spoof Science" videos. The only problem is that this takes a ton of work to put together a short video. So, I am just going to talk about what I could have done.
Here is a quick clip of my 4 year old lifting the car.
So, he lifted the car - it maybe be difficult to tell, but he did. HE LIFTED THE CAR! Ok, I know, he only lifted part of the car. If I were to use this in a real Spoof Science video, I would have…
drorzel | June 30, 2010The kerfuffle of the moment in the science blogosphere once again relates to Chris Mooney, who is pretty much a kerfuffle looking for a place to happen at this point. This time around it centers around a Washington Post op-ed that is basically the executive summary of a American Academy of Arts and Sciences paper that is itself the executive summary version of a series of four workshops on science and the public. You can get a reasonable sense of the kerfuffle from the links in Chris's responses to the responses.
I'm currently making one of my intermittent attempts to be a better person--…
rallain | June 15, 2010Pre Reqs: electric potential, electric field, work-energy
To start, remember that for a constant electric field the change in electric potential energy would be:
WARNING: that is only for a constant electric field. I know you will be tempted later to use this for a different electric field, but DON'T DO IT. But if not that, then how do find the change in electric potential for a point charge? Let me start with a conceptual question. Suppose there were two point charges, both positive but one is held in place. If I hold the other point charge a distance r away from the other charge and…
rallain | June 14, 2010Pre Reqs: Electric Field, Work-Energy, Potential Energy
If you are already familiar with the topics listed in the pre-reqs above, this will be uber-simple.
Potential energy - short version
The work-energy principle basically says:
In this most basic form, the energy is just kinetic energy (if you are not going near the speed of light). BUT...if you have a force that is conservative (meaning the work done does not depend on the path you take), then you can make it a potential energy and move it to the other side.
Warning: you can not have a force and have that force do both work AND be a…
rallain | June 11, 2010Back to the discussion about hiding an electric motor in a pro racing cycle. Before, I looked at a video of Fabian Cancellara to see how his speed and acceleration compare to other bikers. The claim on the internet is that he pulls away so fast that he must have a motor hidden in his bike.
Just to be completely clear, I don't think he is cheating. Then why bother? If you ask that then this must be the first time you reading this blog. I welcome you. No, but really, this is what scientists do. How hard would it be to cheat?
From my analysis, it seems that a person could ride like he…
rallain | June 7, 2010As part of the Ask a ScienceBlogger series, reader Jim Swanson asks:
When I open the dishwasher after washing and the contents are still hot, why do the glass and ceramic items dry off more quickly than the plastic items?
This is a great question. Great because it is something most everyone can relate to and great because there is some good science. Really, this shows the difference between temperature and thermal energy. I think the common idea is that temperature is a measure of the energy something has - but this isn't quite true.
Ok, let me first start with a sample case. Suppose you…
rallain | June 6, 2010So, I hear you are starting your second semester of physics. One of the cool things about physics is that the second semester still uses stuff from the first semester. Maybe you forgot some of that stuff, so here are the bare essentials you will need to get by (this is assuming you are in the algebra-based second semester of physics)
Vectors
Really, just about the entire semester course is about the electric and magnetic field. Both of these are easiest to represent as vectors. So, you pretty much need to know how to deal with vectors. Here are some reviews:
How do you represent vectors…
cagapakis | June 2, 2010Biosafety has been on everyone's mind this week after the announcement of the J. Craig Venter Institute's successful transplantation of a synthetic genome. What horrible pathogen will future bioengineers be able to design? What unforeseeable environmental catastrophe will befall us upon the release of genetically engineered bacteria? These are hugely important questions as research in synthetic biology moves forward, being discussed in congressional hearings and as an integral part of every new synthetic biology design.
As the major proposed goal of a great deal of synthetic biology research…
rallain | May 31, 2010So suppose you saw something that looked like this:
This is a ball shot out of a shooter device. Well, it is a vypthon animation of a ball. What would you do if you came to see this video? If I had not made it, I would say it is an unrealistic video. It does not agree with my basic model of how things move after being thrown or shot or whatever. Interestingly (but unrelated) there was a set of physics questions that showed different possible paths of a thrown ball. The path representing the motion above was a common choice.
Like I said, I made that animation. Here is another one. In…
rallain | May 19, 2010A new video from the Red Bull Stratos Jump guys came out. Here it is:
This reminds me of an unanswered question about the Stratos jump that I didn't address on my last post on this topic. Commenter Long Drop asked about how much Felix would heat up as he falls from 120,000 feet. This is a great question. The first, off the bat answer is that he won't heat up too much. Why do I say this? Well, when Joe Kittinger jumped from over 100,000 feet and didn't melt. Still, this is a great thing to calculate.
How do you calculate something like this? I will look at this in terms of energy. For…
rallain | May 17, 2010Grades are in. So, let me just say a couple of trends that I saw on the physical science final exam.
Gravity on the moon
I asked the question: "why is the gravitational force on an astronaut less on the moon than on Earth?"
The simplest answer is that the gravitational field on the moon is smaller than on Earth (I would accept that answer). Why is this? It is because the moon as a much smaller mass even though it also has a smaller radius (that idea is rather complicated for this class - that gravitational force depends on both mass and radius). I would also take "the mass is smaller" as…
revere | May 13, 2010BP has this great reputation for being an environmentally friendly and responsible company. I know it because their incessant television ads tell me it's true. The ones that flank the national news stories about their horrendous safety record of explosions and worker deaths or their catastrophic oil spills. Those ads. When something happens they start the noise machine and appear to be the innocent party let down by their lessee.
BP ("British Petroleum") is a British Company operating in the US. A US company operating in Britain is called Innospec. You probably never heard of them because…
rallain | May 6, 2010I already mentioned the MythBusters' crashing two cars episode where they correctly doubled the speed of a pendulum type object. Overall, this was a very visual (although expensive) demo. There was one part that left a sour taste in my mouth - the final explanation from the narrator. First, they showed this.
And then they had an explanation that went something very similar to to this (after restating what the sign above said)
"Although the two-car crash doubles the speed, the energy the crash is transferred to twice the mass resulting in a crash that looks like just one car hitting a wall…
rallain | May 6, 2010In the last episode of MythBusters, Adam and Jamie wanted to test something that Jamie had said earlier:
"Two cars crashing head on at 50 mph is the same as one car crashing into a wall at 100 mph"
Jamie was wrong, but that is not what I am going to talk about. Instead, I am going to talk about Adam's small scale test of this situation. Really, it was a nice set up. Basically, he wanted to collide something into a wall at one speed and then double that speed. Then he was going to collide two things together at the lower speed. He had a cool way of measuring the collision. He put a piece…
elerner | May 4, 2010Two weeks ago (on Earth Day, no less), what is destined to become the biggest ecological disaster in history began as the Deepwater Horizon drilling rig exploded. Situated 50 miles off the Louisiana coast, the well is still gushing oil and the growing slick is now making landfall. While this disaster will continue to unfold for some time, many are already thinking about the long-term consequences. Josh Rosenau of Thoughts from Kansas ponders a "corporate death penalty" for BP, James Hrynyshyn of Class M considers the impacts of a similar disaster in harder-to-reach terrain, and Seed Magazine'…
rallain | May 3, 2010This video seems like it is getting popular, but maybe that is because it is so awesome.
Maybe it is just me, but I find this video very visually satisfying. I love the way they compare the different runners.
Anyway, there is some physics here. Commenter Ben sent me the link to this video (thanks!) with some great questions. Which of the runners has a greater kinetic energy? What about the power? These aren't too difficult to answer, but the first thing is to get the data. There are several options (including just using a stop watch). But no, that is not good enough for me. Instead, I…
rallain | April 22, 2010I wasn't paying attention. Earth Day is today. If I would have thought of this before, I could have done something awesome. Instead, here are some reposts related to the Earth and energy. They have been sitting for a while in my post-compost, so they are nice and smelly.
Most of these deal with Earth-type stuff and energy.
Rotation of the Earth as an energy source. What if we could some how use the rotational energy of the Earth? How much would we have to slow it down to get something useful?
Solar Powered motorcycle - possible? There was this story about an electric motorcycle that is…