You can add gravity to an object with using Rigidbody. If you read the following article, you would understand how to add gravity.
You can implement such interaction functions which allow users to operate in a STYLY scene with using STYLY Interaction SDK. The following article is the manual of STYLY Interaction SDK.
I'm keen to see if i can add gravity to a game object in STYLY or PlayMaker?
I'd like to allow a user to pickup and drop an object back onto a table.