simple bits

looking at the fluid, lifelike way these creatures walk and roll and slink across the screen you might think that there must be some very complicated stuff going on behind the scenes. well fear not, it's actually very simple. it only looks complicated because lots of simple bits are working together

when simple bits work together you can get emergent behaviour. that means that the system as a whole can be more complex and sophisticated than the simple bits that it's made out of

let's look at the bits

masses

masses are simple things that obey a simple law. masses accelerate when a force is applied to them

when a mass is moving it has kinetic energy. the environment absorbs some of this energy when the mass moves through the air or collides with surfaces. this loss of energy makes masses slow down

here is a mass; you can pick it up by dragging it upward with your mouse. when you let go the force of gravity makes it accelerate back down to the ground

friction with the air and the ground slows the mass down and makes it come to a rest rather than bouncing forever

springs

springs connect masses. the spring applies forces to the masses when it is stretched or squashed. the spring force obeys a simple law, the force is in proportion to the distance that the spring is stretched or squashed

here's a spring with a graph showing strength of the push and pull force on the mass. drag the mass around with your mouse and get a feel for how the force is in proportion to the amount that you stretch or squash the spring

muscles

muscles are exactly like springs with one simple difference. a spring has a fixed length at which it is at rest and does not apply forces to its masses. with a muscle this length isn't fixed, it changes over time, making the muscle push and pull (note, in real life muscles don't push, they only pull). a wave pattern is used to control the way these muscles expand and contract over time

here you can see the muscle get bigger and smaller in time to the movement of the wave

working together

that's all the bits you need to make moving creatures. they're all pretty simple, but they're also pretty boring. it gets interesting when you put all those bits together

play with some of the ready made creatures or practice building your own and you'll be surprised by how many different lifelike moving creations you can make by getting all the simple bits to work together