need help to make my code flexible.

I started writing a physics engine in Java. I need to write the code in flexible manner.
I currently used one graphic object "rectangle" i need to any number of such objects flexibility.

I need to isolate the each object behaver with graphics object.

example velocity position and acceleration etc of the mass should be maintained in individual class.

please help me to make this code flexible.

That's not really how this works. If you want help, post an SSCCE that demonstrates what you're talking about. Make it easy for people to help you.