In order to test the hypothesis that hot water produces more bubbles when it is mixed with dish soap, certain conditions should be kept constant during the experimentation. The amount of the water and the dish soap used in the experiment need to remain the same, as the effect of these are not being observed in the experiment. However, the temperature of the water needs to be different each time so that the effect of hot water on the production of bubbles can be known.
Hence, the answer is 'the water, and dish soap amount should be same while the temperature of the water should be different'.
Sleep is an example. Circadian rythms are biological processes that repeats itself within a certain time frame, as sleep repeats itself approximately once every day.
