Cohesion is a property of liquids. Water is very cohesive, it sticks to itself.
I like using a cohesion activity when a group of students needs to learn to work in teams. This can lead to a discussion about being a cohesive group.
Click on the link for this post to read more and find a link to a free product at my TpT store that includes a take home activity and a dozen copyright free images you can use to introduce this topic.