One way that rain drops form is called accretion. This is the process by which cloud droplets (very tiny drops of liquid water forming clouds) combine forming larger drops. This happen when the drops bump into each as well as when they get very near each other.
Water molecules have an attraction for each other, so when they are near each other, they tend to draw together and combine. This attraction is called cohesion.
Discover for Yourself
Place a 12-inch (30-cm) piece of wax paper on a flat, steady surface, such as a table. Dip your finger into a cup of tap water and allow 3 to 4 drops of water to drop on the paper about 2 inches (5 cm) apart. Using a toothpick, move one of the water drops toward a second drop. Observe what happens when the drops get near each other. Repeat with the remaining water drops.
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