James joule carefully measured the difference in temperature of the water at the top and bottom of a waterfall. Why did he expect a difference

He expected a difference due to a change in potential energy

Explanation:

He was hypothesizing that the potential energy of the water changed as the height dropped and this change in potential energy would thus result in a drop in thermal energy and thus a drop in temperature. This would then lead to a temperature difference.

positive reinforcement? ?

there is no correct list among the choices you've provided.

the list might look something like this:

-- baby human

-- piccolo

-- flute

-- soprano singer

-- trumpet

-- tenor singer

-- trombone

-- baritone singer

-- baritone horn

-- bass singer

-- tuba

since i had to make up the list myself, i made it easy on myself, and i didn't try to shuffle the string instruments and woodwinds into it too.