My daughter is 5 years old; if your kid is anything like mine they probably ask a ton of questions most of them around “why”. One day she was in the shower asking why the water rolls down the shower door and I thought it was a great time to talk to her about the magical properties of water.
You may or may not remember when the famous magic act (among other things) Penn and Teller got people to sign a petition banning “dihydrogen monoxide” which is just a fancy way of saying water. Water is a pretty awesome chemical compound which most of us know as H2O which means that is has two (di-) hydrogen atoms and one (mono-) oxygen atom.
But when these hydrogens and oxygen come together something special happens. They create what is called a polar covalent bond. Covalent just means they share electrons (the tiny negatively charged particles in an atom) and polar means they share them unequally. Imagine a game of tug of war where oxygen is an adult and hydrogen is a child. Who’s going to win the tug of war? The adult. Oxygen wins the tug of war for electrons so they hang out closer to oxygen most of the time giving oxygen a slightly negative charge and hydrogen a slightly positive; it’s only slightly because oxygen doesn’t hoard the electrons and keep them away from hydrogen permanently — they still share them but it’s a disgruntled sharing. Much like an older sibling being forced to share a toy with a younger sibling.
These partial positive and negative charges give the water some magnetic or velcro like qualities resulting in the magic that happens:
- Cohesion — cohesion is where the positive end of one water molecule likes the negative end of a different water molecule and they stick together. This is how water droplets actually form because the water molecules actually hold onto each other to form the drop.
- Adhesion — adhesion is where the water sticks to another substance. When water sticks to glass or dangles from the faucet before it makes the irritating “drip drip drip” that’s where you see adhesion in action.
- Capillary Action — if your kid has ever asked how trees get water from their roots to to the top leaves — it happens through capillary action. Capillary action is like the water droplets all holding hands and then climbing up the small tubes inside plants (xylem) Water holding hands is the cohesion and then using the sides of the small tube to ninja climb up is adhesion.
- Surface Tension — last but not least cohesion can also create surface tension which is like the “skin” on water than bugs like water striders can walk on. The water molecules are all holding hands (cohesion) but they like to hold hands really tightly to the water molecules around them “don’t let go George!”. Surface tension is also responsible for the forming of a drop into a spherical shape because the water molecules are all trying to hold onto each other.
There are a couple easy experiments you can have your kids do to test some of the properties of water:
- Surface Tension — either gather a bunch of random household stuff (i.e. paperclips, needles, pennies, powdered pepper, legos, etc…) or ask your child(ren) to gather stuff and ask them if they think these items can float on the water or not. Then get a bowl or cup of water and test it. You might have to test it a few times because some of these items need to be placed gently on the surface of the water to float and depending on your child(ren)’s fine motor control you might have to help them with it. Things like paperclips and needles should float but need to be placed gently. Sprinkle pepper or another spice (darker colors are easier to see) and watch it float on the surface of the water.
- Bubble making — Bubbles are a combination of water and soap with maybe a few other ingredients (i.e. glycerin) to try and decrease the surface tension of water just enough to create a bubble but not too much that the bubble pops right away. The cohesion of the water is what holds the bubble together and gives most bubbles the spherical shape but the soap allows the water to expand enough to let the air in. Let your child(ren) experiment with what amount of soap and water (or what kinds of soap) make the best, biggest, or longest lasting bubbles. This is a great opportunity to just let kids play around and see what happens. Give them soap or maybe give different types of soap (dish soap, laundry detergent, hand soap) and see who can make the biggest bubble.
Play, have fun, and get messy exploring the properties of water!