screen should unfold seamlessly
the scroll bounce typically at the end of a screen needs to be "overcome" in order to scroll forward.
communicating resistance; hardship; difficulty
bounce elasticity: how 'spring-like' or snappy the bounce is
bounce position: the position of the bounce on the screen
bounce extent: the extent the user needs to scroll in order to overcome the bounce to move on
bounce count: the number of times the user needs to bounce the scroll in order to move on
