Randomly Floating, Draggable, Collision Dection - oh my!

Yes, I’ve reviewed the lessons for random motion, collision detection, drag n drop… but I haven’t been able to put them together like this: http://www.aliceandolivia.com/#/accessories

How did they do it? I love how you can “toss” the items with varying velocities and they knock into each other. Please someone point me to an answer, tutorial, or more examples.