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Archive for November, 2011

Suspense at the Gym

Imagine the following… You’re on your back, doing your last repetition of bench press. You put a bit more weight than usual (80kg, actually), and with a last feat of strength and a distorted smile of triumph, you complete the rep and put the bar back. You take a breath to savor the moment, stand up, take a sip of water from your bottle, and go to the side to take the weights off. Wait, what are you doing?

There’s a lot of weight on the other side of the bar! Won’t the bar flip over if you take the weights off on this side? Do you have to go back and forth and gradually take the weights off? You don’t know what to do, you’re kinda scared to remove the weights, you’re still panting, and you suddenly wish you’d read a blog talking about pivot points.

Center of Mass
A typical olympic bar weighs 20kg (45 lbs), and you put 80kg in weights, which totals to 100 kg. When the weights are on each side, the system’s center of mass is at the middle.

What happens when the weights on one side are removed? The center of mass is shifted towards the weighted side. The bar will flip if the center of mass goes beyond the hook.

So, will 40kg of weight be enough to flip the bar?

The Barbell
First, let’s define the barbell and weight plates. Everything is different everywhere, but I’m trying to stay as close to reality as possible. The barbell we’re using is based on a normal olympic barbell. Assuming a constant volumetric mass (density), you can get the weight of the different components.

Let’s also define our weight plate set.

Let’s also assume that, with your current set-up, the hook (pivot point) is 0.100 meter (10 centimeters) from the larger part where you put the weights, so 0.545 meter from the end. Also, for the example, your 40 kg weight plates are: 3× 10 kg + 2× 5 kg.

40 Kilograms on One Side
How can you know if the bar is going to fall? The farther from the pivot point a weight is, the heavier its impact will be. For example, if you have a 5 kg weight 0.1 meter from the pivot, its impact will be less than the same weight a meter away. As a matter of fact, it will have ten times less impact (1 ÷ 0.1).

It’s not so easy, though. We don’t have pinpoint weights. They are spread out, so we need to use integrals. Let’s first calculate how the barbell will act around the pivot point.

You can calculate how much the weight is spread out by dividing the weight by its length. For example, the 10 kg weight is spread over 0.026 meter, so it is 10kg / 0.026m = 385kg/m. This will be used during the integral calculations.

Now, the farther the weight is, the more impact it has on the system. This is linearly proportional to the distance.

By calculating the area under the curve (the integral), we can compare the two sides of the pivot. The heavier side will win and bring the bar down. Of course, if the left side is heavier, the bar will just rest on the left hook and stay there.

With some calculations (which will be seen shortly), we can learn that the left side is 13.28kg·m, or equivalent to a 13.28kg weight placed a meter away from the pivot, while the right side is equivalent to a 12.17kg weight a meter on the other side. For simplicity, this will be called the impact.

Left side is heavier, so that’s enough to keep the bar on the hooks, but the choice of weights could definitely be better. The weights that are farther have a lot more impact – the two 5kg have a 4.76kg·m impact, compared to the three 10kg’s 5.23kg·m impact. If we would have chosen four 10kg, they would have had a total impact of 7.49kg·m. Two 20kg would have a 6.8kg·m impact.

Mathematics
What is the impact of the barbell alone? We can split the bar into its constituents, depending on the position.

We can formulate the following integrals

and, knowing the density of the constituents and their position, calculate everything.

That means that if the added weights’ impact is less than 11.1kg·m (13.28 – 2.18), the bar will not fall.

The rest is similar. If you have, for example, a stack of twenty 1.25kg, their impact will be 8.375kg·m (integral from 0.135m to 0.535m, with density 62.5kg/m).

When Will the Bar Fall?
Turns out that for normal weight ranges, it’s pretty hard to make the bar fall.

If you take a single 25kg weight and place it at the very end, it will be enough to cause a crash. A single 20kg at the end will not, though.

Under a smart weight selection, three 20kg weights will be just enough to tilt the bar. If it happens, it means you were bench-pressing 120kg (264lbs), and at that weight, you should have a spotter.

Categories: Science

Minimalism in the Living Room

Ever since I had enough money to buy a computer, I always had the huge powerful ones. At first it was the games, then the video-editing, then just because I wanted the latest technology so that my applications would run quickly and smoothly.

That changed recently as I began to understand the rise of web applications and decentralization. Software is now run on servers, and their interface shown to you through your selected browser. Cross-platform is less and less a problem, though it now lies with cross-browser. Your photos, files, and data are on the cloud. The time when the only thing you need is a browser is quickly coming.

I want to get rid of my huge computer. I also have a handy laptop, and if possible, I’d like to get rid of it too. I want to clean the living room, and be able to look around and not feel visually attacked by all the things around me!

A part of my job is to design web sites, and I’ve become more and more interested in minimalism, or at least in a way to show the data in the most simple way. User experience is very important, and rely in small part on removing the useless visual clutters. Why not do the same in my living room? I look around… The kitchen is not bad – a couple fruits slowly ripening on the counter, and some small appliances in a corner next to the window. The living room is something else. Clockwise: a bookcase with some books, movies, and random stuff, followed by a huge thousand-dollar desk, a seldom-used PS3, a 32″ LCD TV, a 21″ LCD monitor, and a laser printer. Under the desk, partially hidden by an expensive wheeled chair, lies the beast, casting a blue glow on a huge powerbar and a web of wires and cords.

What if I sell the monitor, give the computer and printer to someone, sell the bookcase, build a smaller one, sell the huge desk, hang the TV on the wall, and build a minimalist place to store the PS3 and the few movies? I could even get rid of the PS3 and buy a blu-ray reader. How would that look?

I stopped video-editing a couple years ago, but I am still using my computer to draw and to program, with the occasional movie. I think everything else I do these days is through the internet. I guess I could do that with my laptop, but I feel the wind of change is stronger than that. I want to change everything. I want my home experience (related to computers) to be limited to a tablet (Apple or Samsung – I haven’t made my choice yet).

After some searching, I learned that it is possible to use a Wacom tablet on the web, which means it is possible to draw without the need for an installed application. I first tried the deviantART Muro web app, made a drawing, and then found out they don’t have a crop tool. The drawing was ok, though, once I got used to it (about 5 minutes). There is also Autodesk’s Sketchbook, a 50$ windows application, which can be had as an iPad app for 5$. Didn’t try it yet, but it looks promising, if you combine it with a Wacom pen for the iPad. I’ll have to test these.

Second is the programming. It seems Cloud9 has good reviews. You can set it to work on a GitHub account pretty easily. At work, I program with Visual Studio, and I guess I could use the opportunity to finally learn the simpler and more attractive Python / Django at home. Didn’t do much research on that, but programming on the web sure seems easier said than done. Maybe I could completely stop programming at home? Or maybe stay an hour or two after work to continue my personal projects? I could then spend my free time to read, or take a walk…

For the movies, there is of course streaming web sites like Netflix. Also, the movies you buy can be bought as downloads (iTunes). I’ll have to check if I can output a movie from the iPad to the tv…

I’ll wait for the iPad 3 and the next Samsung tablet, and compare the two. Then I’ll make a decision about my living room.

Categories: Thinking

Working Parents

2011/11/22 2 comments

A recent trend among couples is that both are working. They meet, get married, have kids, but both are so dependent on material possessions or various expensive services that they continue working and just give their children to some caretaker every day of the week. Or maybe they never thought about it that much, and continued their day-to-day lives. Or maybe they have too much debt…

You rarely saw that in the 1920s, 1950s, even 1980s. Women requested more and more rights, and wanted the freedom to do what they wanted. I’m not saying it’s a bad thing (far from it), but a consequence of this newly found financial independence is that they want to keep it, and not rely on someone else. Also, we have a society so centered on material possessions that we are willing to forget family values.

I once started the subject with someone. What she replied was “I went to the university for this job, why would I throw it away?” What better reason would you need than for your children?

Please don’t get me wrong – I’m not saying it’s because women continued to work, but because both parents kept working. If my future love wants to keep working after we get kids, I’ll seriously consider giving up my own job and take care of the kids and the house, all day long.

Think about how your parents were when you were a kid. Chances are that, if you’re about my age or older, your mother was staying home. Dad left home in the morning, after breakfast. Mom took care of you, played with you, prepared lunch, did some cleaning, washed some laundry, and prepared the dinner just before dad got back from work. Then what? Both were having a nice evening, doing relaxing things, playing with you, or whatever.

Your mother had a job – a very demanding one, and unpaid, but consider the alternative… Both your parents wake up and hurry to eat breakfast and dress you, and both take their respective car in opposite directions, one of them bringing you to a daycare center. You stay there, playing with friends, until one of your parents come and get you back. Both parents get back home, it’s 17h30, dinner is not made, and they hurry to prepare something quick (and unhealthy) before spending the evening doing a batch of laundry and cleaning the kitchen, to finally take a breath 20 minutes in front of the TV before going to bed. You, all that time, couldn’t get your parents’ attention, and had to play by yourself or with your siblings. And then, it’s the weekend, and your parents spend it working and cleaning everything that they didn’t have enough time to during the week.

This is a trend, and it’s a totally voluntary one. People right now are preferring a life of stress and higher pay grades, instead of spending quality time with their family. Yes, they can afford a 60″ plasma TV, and the latest PC, and they can give a smartphone to each of their kids even if they costs 60$ per month. But at what cost?

You mother had a job – and in every aspect of it, it’s the most rewarding job ever. You help your kids grow up, see them take their first steps, you’re there to hug them when they hurt themselves (they always do), and most important of all, you take your time and give them your values. Not the values of a daycare provider – I’m not saying their values are wrong, just that they are not yours.

That leads me to wonder exactly why our society is like that. What has become of the American dream? Was “keeping up with the Joneses” the problem? I guess it’s a possibility. Ads are made in such a way that we feel compelled to buy stuff, all the time. Remember the excitation just before you buy something? It’s like a drug. We are fed images of things that we don’t need, and are “told” that we “should buy it” because “normal people” have it.

Does a family really need two jobs? It costs an average of 10,000$ per year for daycare, per child. Plus a second car (let’s say 5,000$ per year, over five years), plus gas, plus the extra cost of ready-to-eat food… Maybe add to that a vacation, because of the added stress? All these extra expenses that occur only as consequences to having both parents working. After taxes, you’re left with a net amount of what… 1,000$? 10,000$? 20,000$?

I urge people to consider a life more centered on family values, and less on material possessions. Do you have debts? Pay it back, and as soon as possible! Buy a used car instead of a brand-new 35,000$ one (or for crying out loud, buy the 20,000$ one!). Do you really need *all* those channels on your tv? Do you really need that expensive piece of clothing with a brand on it? Cook instead of going so often to the restaurant. There are so many expensive things that we don’t see around us. And when you are done with your debt, invest what you have left – it will pay in the long run.

Maman, papa, merci du fond du coeur pour ce que vous avez fait pour Mélanie et moi.

Categories: Thinking

Happy Birthday!

2011/11/18 2 comments

I learned recently that Time-Warner has the copyright to the song “Happy Birthday to You”. Technically, they can sue you if you sing it publicly.

This has got to be the most memorable song everyone sing, every year, since their first birthday. Why is there even a copyright on such a happy song? Because TW reportedly receive around 2 million dollars in royalties, evey year. It can cost several thousand dollars to use the song in a movie. And the suing thing was not even a joke – though they were covered in shame for doing so, some smartass somewhere thought it was worthwhile to sue a group of camping scout girls.

I really need to know what they were thinking, if they really thought they could get a lot of money out of this, and who approved the action. After the media coverage, they apparently settled for a symbolic 1 cent (if I remember correctly?), but the intent was there from the beginning.

Companies like this are the ones that we should boycott, but how exactly can we do that? TW owns New Line Cinema, Time inc, and HBO, along with a dozen other subsidiaries. That’s pretty big. We can boycott companies like Sony in favor of Samsung, for example, but if I want to boycott New Line Cinema, I’ll notice pretty quickly that no other film studio has another version of the Lord of the Rings.

So I guess my question would be: why the *fuck* isn’t Time-Warner giving this song back to the public domain, where it belongs? Yeah, yeah… Money…

Categories: Uncategorized

Pendulum Waves

Did you see the Pendulum Waves video?

It shows a set of properly configured pendulums. When viewed from the side, the brain can recognize different patterns as the bobs swing back and forth at different speed.

The experiment is set up with 15 bobs. The first one is set to do 51 cycles in 60 seconds, the second is set to do 52 cycles in 60 seconds, all the way to the last bob, which is set to do 65 cycles in 60 seconds.

One Pendulum
Let’s look at a single pendulum. You bring the bob at a 30° angle, and let it go. It’s position over time would be defined as a sine wave.

Two Pendulums
Let’s see what happens if you have two pendulums, but they are not synchronized. Pendulum α does 3 cycles in a second, while pendulum β does only 2. Their displacement over time would look like this:

With this graph, we can easily see that at the beginning and at every second, both pendulums are at the left. Also, at 0.5 and 1.5 seconds, pendulum α is at the right, while pendulum β is at the left. This is what our brain recognize as a pattern.

Fifteen Pendulums
Patterns become more apparent with more pendulums, but they can also look more random. The brain recognize when the bobs form groups that are going in the same way, or form a shape (here, this is typically a wave).

The brain seems to have some difficulties to notice patterns made of five groups and more. Forms can also become hard to notice when there is not enough bobs (resolution) to correctly show the wave. For example, when the bobs are first let go in the video, they form a wave of increasing frequency, until, after about 13 or 14 seconds, the brain can’t make out the wave anymore.

Mathematics
The most important thing in the experiment is to carefully time the bobs. How to do that?  The formula to find a pendulum’s cycle (taken from wikipedia, because this was far beyond my skills) is

In the video, the initial angle seems to be around 30°, so we can use this value (and greatly reduce the complexity of the formula). Also, gravity on Earth is 9.80665 m/s^2. That simplifies the formula to
For those who care, the graph of the angle modifier looks like this:
If we want the first bob to oscillate 51 times per minute,
we have to set the length of cord to almost one third of a meter, which is pretty much what we can see in the video. With the same formula, we can find that the quickest bob should have a 0.20448 meter cord.

Furthermore, the dark-blue curve on the graph is the same curve that the bobs make initially in the video. Trivia: for a bob to oscillate once per minute, it would need a cord almost 1 kilometer long. For it to oscillate once per day, the cord would be longer than the distance from the Sun to Saturn.

I have made a small online calculator for such pendulums. You can find it at my web site. At the time of writing, giving the data to find the angle is not implemented (I will have to code a brute-force algorithm for that, or an approximation), but you can easily find the other data.

Categories: Science