svg and javascript

I am new to javascript and I want to implement a pulley in which I need to draw a circle using SVG to which 2 strings are attached touching to its circumference at diameter. Also I want to show 2 rectangular blocks attached to these strings at the end which will have 2 weights w1 an w2. Taking w1 and w2 as inputs from the user, I need to calculate the tension on the string as T1 = w1*g. Also if w1 > w2 block will move downwards along with the开发者_如何学C string. How can I implement it using SVG and Javascript?

Take a look at Raphael JS which I quote:

Raphaël is a small JavaScript library that should simplify your work with vector graphics on the web.