Water is one of Earth's most precious and plentiful resources. It makes up 60 to 70 percent
of our bodies and covers 70 percent of the Earth's surface. Water has so many unique and fascinating
characteristics! Today we'll learn about two different properties of water, adhesion and
cohesion, as we perform the Water Drop Experiment from Lesson three of the Weather and Water science
unit from The Good and the Beautiful. In the simplest terms, adhesion means that water likes to
stick to other things. The particles in water have a tendency to seek other particles from different
substances and adhere, or stick, to them. This is why after washing your hands, your hands
will stay wet for a few minutes if you do not dry them. Similarly, cohesion means that water likes
to stick to itself. The molecules found in water like to cluster together, forming droplets. This
is why rain falls in drops that hold together until they burst when they hit the ground.
Let's see these properties of water in action. In today's experiment, we will drop water onto
a dry penny and onto a wet penny to test adhesion and cohesion. We will count how
many drops we add to each penny and observe how many drops each penny can hold. before we begin,
turn to the Water Drop Experiment page in Lesson Three of your student journal.
Take a moment and write down your hypotheses, which are your predictions of what you think will
happen with the pennies. How many drops of water do you think each penny will be able to hold?
Which penny will hold more water drops? Pause the video now to complete your predictions.
Now that you have written down your predictions, it is time to conduct the experiment. For this
experiment, we will need two pennies, a glass of water, and an eyedropper or medicine dropper.
I'll fill the medicine dropper with water.
Now, I will carefully drop one drop of water at a time onto the dry penny surface.
1, 2
3, 4
5, 6
7, 8
9, 10
Notice what happens to the water on the dry penny? It pools together to form one big water
droplet that holds its shape! Even when more water drops are added, this is an example of
cohesion because the individual water drops are sticking together to make one big water drop.
It is also an example of adhesion, because the water drops are sticking to the penny and not
spilling off. Let's see how many more drops we can add before the water spills off the penny!
11, 12
13, 14
15, 16
17, 18
19, 20
21, 22
23, 24
25, 26
Wow! This penny held 25 drops. Pause the video
now and record the results for the dry penny in your student journal.
Now we will take the second Penny and dunk it in the glass of water, getting it completely wet.
I'll place the wet penny here and repeat the same process of dropping water slowly onto its surface.
Let's count how many water drops we're able to fit on the wet penny before the water spills off.
1, 2
3, 4
5, 6
7, 8
9, 10
11, 12
13, 14
15, 16
17, 18
19, 20
21, 22
This wet penny held 21 drops! The drops of water sticking to the water already
on the penny is another example of cohesion. Pause the video now and
record the results for the wet penny in your student journal.
Take a look back at your predictions. Were you right? Did your findings surprise you?
I hope you enjoyed this experiment! Water sure is an amazing part of God's creation.