# Core Dump: Physics Is More Than Just Gravity

Say “physics-based game” and usually games like Angry Birds come to mind: something that involves gravity and collisions. Games like Happy Hills, Kickin’ Momma, or Saving Private Sheep all involve forces that fling projectiles which then bounce around. Of course, there are also Rube Goldberg-type games that involve dropping marbles or other balls along ramps, chutes, and conveyors to trip switches and reach a goal (like BallFallDown, for instance).

But physics isn’t just about velocity and gravity, right? There’s also fluid dynamics, friction, and electromagnetism, for starters. Here are a few of the physics-based iOS apps I’ve been playing lately. Some fall into the more traditional type, but there are a few that stand out with more seldom-seen game mechanics, too.

Sprinkle: put out fires before the houses burn!

Sprinkle – \$1.99 (or free version)

First up: fluid dynamics! Sprinkle is a puzzle game that has you putting out fires with an adjustable fire truck. Little tiny creatures stand outside their huts, waiting for you to rescue them. Your fire truck sits on the left side of the screen, and you can raise and lower the hose, as well as rotate the angle of the spray. Push the big red button in the bottom corner to spray. The trick, though, is that it’s not enough to just hit the fire with the water — the water has to be in contact with the fire long enough to actually put it out, and that’s where it can get tricky. Plus the water will flow away or even seep down into the ground, so you really have to watch what you’re doing. Or, sometimes water you’ve already sprayed will flow back toward you, which means you have to wait for it to drain a bit … which means the fire spreads.

On top of that, there are puzzles to be solved — sometimes you’ll need to use the water to push things around, like shoving a boulder onto a button to open or shut doors and activate other things. There are some puzzles that have objects you can just drag around directly with your finger. Oh, and finally: you have a limited supply of water. The more water you have at the end of a level, the more “drops” you get, which you’ll need to unlock further levels. But if you run out of water and the fires aren’t out yet, the poor little guys lose their homes. There are 72 levels (so far), some of them incredibly difficult. I haven’t been able to unlock all of them yet, but I’m working on it. You can get the free version to try it out before you buy.

Sprinkle Jr. uses the same idea but simplifies it for kids.

Sprinkle Junior – \$1.99

Sprinkle Junior takes the same basic idea, but reduces the number of controls and makes easier puzzles. Although the original has very kid-friendly graphics, it can be really tough. The junior edition simplifies several things: first, there’s no limit to the water. Also, you move the hose up and down, but you don’t rotate the head, and also the water shoots automatically as long as you’re touching the hose. There are fewer puzzles (just 22) but they’re all different with some fun features like drums that actually play sounds, or a giant hamburger whose layers will slide off as you spray them. My 5-year-old has really enjoyed this version, even after solving all of the levels.

3 screenshots of Orbital, showing various modes: Gravity, Pure, and Supernova

Orbital – \$2.99

I’ve reviewed Orbital before — it’s one of the earlier apps I put on my iPod touch, and one that I’ve logged many, many hours playing, perhaps close to the number Dave Banks has invested in Skyrim. (Though, in my defense, that’s been over two years of play, often while doing other things.) What’s interesting about this one is that the projectiles have friction: they bounce around but also slow down over distance. In Gravity mode, the projectiles are also attracted to previously-shot projectiles, but in Pure mode they shoot straight, like billiard balls. This isn’t puzzle gaming — it’s simply arcade bliss.

Inertia: Escape Velocity lets you preserve your inertia.

Inertia: Escape Velocity – \$3.99 iPad, \$1.99 iPhone (plus in-app add-ons); or free version

Ah, inertia: resistance to change. It’s what keeps a projectile going in the direction it’s been fired, and what keeps me sitting in my desk chair long after I should have gotten up to do other things. Inertia: Escape Velocity lets you play with inertia: you have a special GRAV suit that lets you turn gravity on and off, which lets your inertia carry you at whatever velocity you had at the time. By turning it on and off, you maneuver yourself through a maze of platforms, force fields, attractors and repulsors, all while collecting parts to repair your ship. Oh, and I nearly forgot the exposed electrical zapper things that kill you when you touch them.

Each level challenges you to make it to the end goal, collect a certain amount of scrap, and do it all within a certain time limit. On top of that, you can get the additional Inferno levels, which are unbelievably difficult and require extremely precise control of your GRAV suit in order to get the special Inferno tokens. Get enough and you can unlock another set of levels.

Inertia is a pretty tricky one, and a fun concept for a platformer. The level selection interface is a bit tiresome, as it shows your ship traveling between galaxies, and each group of levels is further subdivided beneath that. It’d be nice to just be able to scroll quickly through all the available levels. There are other in-app purchases as well, including some boosts that give you particular abilities, but these are more like cheats and you don’t necessarily need all of them. There’s the iPad version, iPhone version, or the free version.