When my parents left my sister and me home alone when we were kids, there were two things we did. One was to turn the convertible couch into a bed, eat endless snacks, and watch Loony Tunes. The other was to put marshmallows in the microwave to see how big they got.
Kids love experimenting with food and household gadgets, but often reserve this potentially dangerous play for a time when parents are away and can’t get mad that the kids have caused crayons to melt and harden in the microwave. Instead of coming home to a house that is under an inch of foam because the kids got it into their heads to put mentos in a soda bottle in the living room, you can perform science experiments in the kitchen with your kids, teaching them about chemistry, physics, the scientific method, and the importance of goggles and a clean-up plan.
The best kitchen science experiments involve stuff you already have in your house: like water, vegetable oil, empty bottles, vinegar, and occasionally milk, string, or paper clips. One of my favorites is creating waves in a bottle, and learning why some waves move at different speeds. It is my favorite because it is easy to create, and the results are broadly applicable.
For this experiment, take an empty plastic bottle. Fill it half way up with water. Screw the lid on. Have your kid gently tilt it from side to side. The waves form quickly, and the movement of the waves causes the bottle to tug at your hands. Next reopen the bottle and fill it to the top with vegetable oil. Reseal it and tilt it again. This time the waves move much more slowly.
The oil and water never mix due to their differing densities, so your kid will want to know why the water flows at a different rate when there is oil on top of it. The answer is all about pressure. When there was just water in the bottle, the only pressure on it was from the air above it, which is essentially uniform throughout the bottle, and the pressure of the water itself. When you tilt the bottle, more water ends up on the low end than on the high end. This greater volume of water means a higher degree of pressure on the water at that end. Water, or any fluid, will move from a high pressure area to a low pressure area. So the water on the fuller side moves toward the water on the less full side. However, because the water has momentum, it overshoots equilibrium, causing a series of slowly diminishing waves to happen in the bottle. When oil is added, there is now additional pressure on all parts of the water. Because oil is less dense than water, there is still less pressure on the part of the bottle with less water and more oil, but the pressures on both ends are much more close to equal. This means that waves still form, but travel more slowly.
This simple experiment can lead into talking to kids about what pressure is, and how air and water exert pressure on whatever is below them, even if what is below them is just more air or water. The simple fact that fluids move from areas of greater pressure to areas of lesser pressure, and that that movement causes waves, can explain a great deal of meteorological phenomena.
We mentioned earlier how we liked putting marshmallows in the microwave Since Easter is coming up, you may find yourself burdened with Peeps, which are inedible squishy toys masquerading as candy. The best thing to do with them is put them in the microwave and watch them turn into Megapeeps.
Then, for educational purposes, you should explain to your kid why they grow so big, whereas most other food you put into the microwave doesn’t. It is because marshmallows have three ingredients: water, sugar, and air. As the microwave heats up the marshmallows, it causes the sugar to soften and the air to expand. Because the sugar is soft, it is pliable and moves with the expanding air. When you take the marshmallow out of the microwave, it cools, the air compresses, and the marshmallow deflates. Because some of the water evaporated, the marshmallow is now harder, and can be molded into a new shape, which it will then keep. So, if you have a box of Peeps, you should expand them in the microwave, cool them, then use them as a material for art projects. They’re basically like sticky play dough, and about as delicious.
Come back next week for a discussion of things in your kitchen that you can set on fire!
(Hint: you can set most anything on fire. The trick is figuring out what you should set on fire.)
(Hint number two: borax and anything with copper in it.)