Thursday, 12 April 2012

it's gravity, Jim, but not as we know it

I’ve just finished Angry Birds * Space (which everyone seems to call Angry Birds in Spaaaace, of course), released March 2012.  So that didn’t last long, either.

This time, the birds and pigs are fighting it out in space, and the birds have rocket drives.  There’s gravity in some places (near planets), and not in other places (not near planets). Only it’s not as simple as that. The existence of a gravitational field is shown by a red disc centred on the planet. Inside the disc there’s gravity, with the force directed towards the centre (I can’t tell if it’s 1/r^2 or constant on my little tiny phone screen); outside there’s no gravity. Gravity just switches on when an object enters the disc. Real gravity in space doesn’t work like that, of course.

Outside the disc, in the no-gravity regions, things travel in straight lines. So far, so good, maybe. But they gradually drift to a halt. No gravity, okay, but friction?? (Which is why the birds' rocket drives are on all the time.)  Real gravity in space doesn’t work like that, of course.

Also, there are some “black holes”: nothing visible at the centre of the gravity field, but stuff does get broken up if it goes there. There are also, confusingly, sometimes large planets with no gravity field at all, that act as hard (but massless!) obstacles. (Cases with invisible gravitating black holes plus visible gravity-free planets are particularly … interesting.)

There are two new birds: a light blue "ice cube" bird which freezes stuff, making it easier to break later, and a purple ("Lazer") bird that boosts in the direction of your tap (instead of the yellow Lazer bird that boosts along its tangent when you tap).

It's a Small World
The planets are very small – Clanger-esque, or even “Little Prince”-like.  In order to erect buildings on these small spheres, there are often large flat platforms. Sometimes this can lead to an almost square planet. Even with these platforms, gravity still points to the centre of the planet, so there is a small resultant force along the direction of the platform. I was delighted to notice, when an ice block was at the end of a platform, it slid towards the centre, overshot, then slid back: simple harmonic motion in action. Yay!

Square planets!
I did this time go for a perfect three stars on all levels.  That’s because the alternate-physics is fun, and three stars often required an interesting solution exploiting the possibilities, especially where planets are so close their gravity-discs overlap. Fortunately there is a helpful little "preview orbit" dotted line, that gives a partial clue to the final trajectory.  (The "Golden Eggsteroid" extra levels are great little spoofs on Space Invaders and the like.)

So, I’m just back from the Science Fiction Eastercon, where I was telling a friend that I’d nearly finished Angry Birds Space. So that’s all three done! (Vanilla, Seasons, Space) There’s also Rio, he said.


I’m now on Rio level four, collecting golden bananas…

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