The Physics of Angry Birds

You know the game, I know you know. Angry Birds. I have an attraction to games like this. You can play for just a little bit at a time (like that) and each time you shoot, you could get a slightly different result. Oh, you don’t know Angry Birds? Well, the basic idea is that you launch these birds (which are apparently angry) with a sling shot. The goal is to knock over some pigs. Seriously, that is the game.

But what about the physics? Do the birds have a constant vertical acceleration? Do they have constant horizontal velocity? Let’s find out, shall we? Oh, why would I do this? Why can’t I just play the dumb game and move on. That is not how I roll. I will analyze this, and you can’t stop me.

I think for later Angry Bird analysis, I will make my own videos. But for now, I will use some of the walkthrough videos provided by Rovio (the creaters of Angry Birds). In particular, I am going to use one of these (Spoiler Alert):

How do you get the data from the bird? I will use my favorite Tracker Video analysis. The nice thing about Tracker (other than being free and running Windows, Mac, and Linux) is that it has a nice feature to handle both panning and zooming videos – calibration point pairs. The basic idea is to mark two features in the video and follow these throughout the clip. By marking the location of these two objects in each frame, Tracker will scale, pan and rotate the data as needed.

One more thing. Scale. What is the scale? Who knows? Let me start with an object that should be in each level – the sling shot. I am going to call the length of this 1 AB.

Now on to the data. Here is a plot of the horizontal (x) position of the bird as a function of time:

What does this mean? This means that the bird was moving at a constant velocity in the x-direction. In this case, the x-velocity is 2.46 AB/s (assuming the video runs in real time). Is this good? Well, suppose this is real physics and real projectile motion. In that case, this would be a force diagram for the bird in the air:

Yes, it is that simple. The only force acting on the bird (if the bird is not moving too fast) would be the gravitational force from the Earth. This is where I see lots of intro-student mistakes. They tend to want to put some force in the horizontal direction because the bird is moving that way. DON’T do that. That is what Aristotle would have you believe, but you don’t want to be in his club. There is no horizontal force in this case – no air resistance.

What about the vertical motion?

Oh, I forgot to point out that the missing data in the graph is from where the bird went off the screen. This also shows the vertical motion having constant acceleration (because the quadratic equation fits so well). Relating this function to the kinematic equation:

The value in front of the t2 term should be 1/2 times the acceleration. This means that the acceleration of the bird (in the vertical direction) is -2 AB/s2. What if this angry bird is actually on Earth? On Earth, the vertical acceleration should be -9.8 m/s2. I can use this to find the length of that sling shot as:

That is one big ole sling shot, 5 meters tall? Wow. Measuring the red bird, it is almost 70 cm tall. That’s a big bird. Big, angry bird.

track video analysis 是个好软件啊。

这几天玩的正HIGH了~~~感觉这个游戏的娱乐性在于偶然性吧

这几天玩的正HIGH了~~~感觉这个游戏的娱乐性在于偶然性吧
q303739744 发表于 2011-1-11 12:32

人家的结论是那个鸟真的很angry，有70cm高，弹弓有5m高。。。。

这软件真是不错啊！

4# goingeast
楼主有没有玩过一个
Ragdoll Blaster - A Physics Puzzler一代有100多关。打穿以后真是爽。觉得那个里面触摸各种物理现象的“手感”更丰富也更有味道。只是有点太学术和沉闷了。论品质我觉得远在angrybird之上。

6# zyf1990 没玩过，我搜了下貌似很专业啊，我试试。

goingeast...这id名儿真不错。。。

goingeast...这id名儿真不错。。。
urunable2c 发表于 2011-1-12 20:37

why？

人家的结论是那个鸟真的很angry，有70cm高，弹弓有5m高。。。。
goingeast 发表于 2011-1-11 14:05

没仔细看。。。我还以为辅助工具之类的。。。