Materialworlds will still work with 256 or 16 colors, but some webpage colorschemes won't look right. InternetExplorer is required because only it supports the ActiveX Documents and Controls that make it relatively easy to incorporate Windows programs into web pages. Getting materialworlds to work on other browsers would entail extensive low level replication of Microsoft's operating system - and we'd prefer to spend our time developing simulations and experiments. See materialworlds editor and webpage tutorial . Very short arrows are drawn just as a straight line, without an arrow head.
Red arrows show the strength and direction of the forces on an object.
Thin headed arrows show the individual forces that combine together to give the triangle headed resultant force. A blue arrow shows the speed and direction of an object's velocity. Unless a simulation prevents it, you can change an object's velocity while the simulation is paused by pulling the velocity arrowhead with the mouse. In some simulations you'll see a bar across an arrow. In some simulations the bonds between objects are colored to indicate if the bond is compressed or stretched.