Cohesion is one of water’s many characteristics. It means that the water molecules stick together. It happens because of the shape of the water molecule.
The area around the oxygen has a negative charge. The area around the hydrogen has a positive charge. The two positives push away from each other. The negative and the positive are attracted to each other. This is like the two sides of a magnet, which you’ll be learning more about another time.
Since there is more than one positive area, one water molecule can attract more than one water molecule to stick to.
When there is a cup of water, or even just a drop of water, the water molecules on the surface are all attracted downward towards the other water, since there is no water above to be attracted to. Since they are all pulling in the same way, it creates a more stable surface. That’s the surface tension. That’s what’s allowing something to float on the surface of the water, when it would sink if it were under the water.
The water molecule’s shape, and how it attracts other water molecules, and how they stick together, all help us understand why water will bead up. The water molecules are attracted inward toward each other.