As you dropped the water onto the penny, what shape did the water make?

Water has a REALLY cool property called cohesion which basically means it likes to stick to itself.  We'll learn WHY it likes to stick to itself in the next section, but right now all you need to know is that water likes water.  If a water droplet can connect with another water droplet, it will. 

It's a lot like playing Red Rover with your friends.  You hold on tight to each other's hands and when someone comes crashing in, you try not to let them through.  If you hold strong enough, then that person gets to join your group and make it bigger.  But if the person runs too hard and fast then it breaks a part your line. 

That's what water does.  If you're careful enough with your drops then the water will connect itself into a larger sphere rather than spilling over.  But if the drops come in too hard or too fast (or eventually if there's just too many of them) then the water dome will spill over.

But why does water like to stick to itself and what are other examples of cohesion?  Let's find out!

Paperclips will usually sink to water.  But if you are REALLY CAREFUL you can get them to float on top. 

Using what we learned from Challenge 1, why do you think the paperclip can float?  

Have you ever belly flopped in water?  How did it feel?
  
We already learned that water likes to stick to itself. That's called cohesion.  Cohesion of water works especially well on the surfaces of water.  We call this surface tension.  Water molecules will pull on each other and stick together as tight as they can, acting like a stretched skin on the top of the water. 

When you use a fork to very carefully lay the paperclip on the water, the surface tension of the water helps keep it up. 

This is how water skippers and other small bugs walk on water!

WHY does water stick to itself?
What happens when you use SOAP?
Can you make a siphon?

Answer these questions,
Get THREE more free challenges,
More simple science explanations,
PLUS a simple science worksheet for kids to follow along and track their progress

ALL FREE.

Because we believe that kids learn best through PLAY.