(2) The evaporation speed of liquid is affected by three factors: liquid temperature, surface area and air velocity on the liquid surface. Therefore, when studying the relationship between evaporation rate and liquid surface area, the idea of control variable method should be adopted, and the temperature should be controlled to be the same as the speed of air flow above the liquid surface, only changing the size of liquid surface area.
So the answer is: (1) The water on the playground dried up quickly after being swept away;
(2) A glass of water, two pieces of glass and a dropper;
(3) (1) Take two drops of liquid with a dropper and put them on two pieces of glass respectively to make the surface areas different;
(2) Put the two glass plates in the same environment (the control temperature and the air velocity above the liquid level are the same);
③ Observe which droplet dries quickly.