An interactive learning object

This is a learning object for learners to learn the concepts and functions about cam, gears, levers and pulleys. It encourages learners to try to build a machine through using these tools. The reasons why I like it are as follows:

--Appropriate academic references are provided

--Clear learning objectives

--Clear instructions

--Help learners to engage effectively with the concept/skill/idea:
Illustrate concepts that are less easily explained through traditional teaching methods

--Easy to use:
Consideration of the general layout of the object, attention to the buttons, menus, text and types of user-object navigation

--User control and freedom:
If users choose a function by mistake, they can safely leave the unwanted state