Showing posts with label Scientific Method. Show all posts

Milk, soap, and food coloring



An easy experiment to show how fats move in liquids.

How does soap work?  What do hydrophilic and hydrophobic mean? This is a good experiment to start some of these discussions.  The fats in the milk are oil based (technically, they're called lipids) and the water in the milk is well, water.   Fats and oils are hydrophobic, which translates into "water fearing".  These fat molecules will clump together so that as few of them touch the water as possible.

Soap is a molecule that has a hydrophobic side and a hydrophilic side. (Hydrophillic ==  water loving. This is useful in our daily lives because the hydrophobic side of soap molecules will bind to oil and grease, and the hydrophilic side of the soap molecule will bind to the water molecules.  Then, when you wash your hands, as the soap gets washed away, the oils and grease are dragged away along with the soap.  

So, back to the experiment.
When you add soap,  you'll see food coloring expand away as all the fat molecules push the food coloring out of the way to get closer to the hydrophobic soap molecules.   Kids of all ages will enjoy "painting" with soap in the milk.  Older kids can start to grasp the concept of hydrophobic vs hydrophilic.

Materials:
Plate
Milk (skim milk works best, but whole milk will also work)
Half and half
Soap [not all soaps work.  Joy dish soap does]
Q-tips or Toothpicks
Food coloring

What I do:
I pour milk into one of the plates. Then, we drop a few drips of food coloring around the plate.  The kids dip their Q-tips into the soap and then poke one of the food coloring drops.  The result should be to see the food coloring expand away from the soap.

To make this an experiment, I get another plate and pour in half-and-half (or a milk with a higher fat content than the one I previously used.).  Before the kids dip their soap into the new plate, I ask them whether the colors will spread more or less than last time, and I ask them why.  This is called 'making a hypothesis' and is crucial to running an experiment.   Then I let them test it out.

What this activity teaches:
Scientific Method.  It's important to have your kids guess (make a hypothesis) about what will happen.  To encourage more experimentation,  ask them what they think would make the colors expand faster?  I.e does warm milk vs cold milk work?  What about adding more dish soap vs adding a little bit?  See what they come up with first before you give them hints.

Hydrophobicity.   Certain materials repel water.  This is a great experiment to start the conversation of what hydrophobicity is, and how it is useful in everyday life.

Sink or swim

Kids test whether their toys sink or float.

This is a really good introduction to the concept of buoyancy.  Before dropping the toy in the water, I made them guess whether it would float or sink.  Then we can talk about some of the similarities of the things the float and the things that sink.  For example, plastic toys seemed to float and metal toys seemed to sink.  I did this experiment indoors, but it's probably best to do it outside if you have concerns about getting your floors wet.  It was also fun (as a parent) to see what my kids decided to test.

 Materials:
A large container (clear is best, but any will do),
Random household objects

 What I do:
I asked the kids to collect some toys that they wanted to test (no batteries, and no stickers).  Before they dropped their toy, I asked them whether they thought it would sink or float, and why.  Then we tested their hypothesis.  If you want to make it seem more like a science experiment, have the kids write down their guess and their results in a "lab notebook"

What this activity teaches:
Scientific Method.  It's important to have your kids guess (make a hypothesis) about whether their toy will sink or float.   For older kids, its easy to have them keep track on a sheet of paper as to which items sunk or float.  Then, ask them for their conclusion as to why something might sink or float.  (Hint: buoyancy is based on whether an item is heavier than the amount of water it displaces)

Buoyancy.  This can be deceptively easy concept.  It's easy to say light things float and heavy things sink,  but then why would a heavy boat float while a penny would sink?  It's all about density and weight vs volume.  This activity is a good introduction to this concept, and gets kids thinking about what makes something float.

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