Have you ever wondered why water sticks to your skin?
When you jump into a ball pool and come out, none of the balls will be stuck on you.
However, when you come out of a pool full of water, all the water doesn’t leave your skin immediately.
Instead, it drips and you stay wet for a good while.
This is caused by two special properties of water – cohesion and adhesion.
In this experiment, water can travel from one cup to another without them being close together or one directly above the other.
The secret? We’re using a string.
- food coloring (optional)
- 2 cups
- a long string (be sure to use cotton twine or strings that can absorb water. Polyester strings won’t do)
- scotch tape
- adult supervision
- Tape one end of the string to the inside bottom of a cup.
- Fill the other cup with water (and food coloring if you want) and put the free end of the string in the water (not taped).
- Lift the cup with water up above the other, but not directly over it. Hold it far enough that the string is taut. Be careful not to pull the string out of either cup.
- Slowly pour the water out of the top cup onto the string. Remember to keep it taut at all times. Observe what happens.
- Now, soak the entire string in water and try again. You should be able to pour the water straight from the top cup to the bottom cup through the string.
This traveling water experiment has demonstrated two important properties of water.
Cohesion: Water molecules are attracted to one another and so they tend to stick together.
Adhesion: Water molecules are also attracted to molecules of other objects and so they tend to stick to objects such as a string.
When you first poured the water, although water molecules were attracted to the string, adhesion wasn’t as strong as gravity pulling the water down.
But when you tried again after soaking the string in water, water molecules were not only attracted to the string, but they were also attracted to the water molecules in the string.
Adhesion and cohesion together prevented the water from dripping straight down.
Instead, the water flowed along the string down to the bottom cup.
- Now that you know about cohesion and adhesion, repeat this experiment using other liquids such as milk, juice, soda and see how cohesion and adhesion vary in each material.
- Using different types of strings to explore more.
More Water Science
Water is such an amazing natural resource. There are endless experiments you can do by utilizing the special water properties.
There are also many books on those fun water facts. Water is cool!