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.

speed

ratio of distance traveled to time interval

net force

vector sum of forces on object

object

source of diverging light rays either luminous or illuminated

don't remove my answer im trying my best to answer them

explanation:

3. dark matter

empty space could also be a simple vacuum