Thursday Teaching {Lava Cups}

Project: Lava Cups

Concept: Floating Continued!

 Today's project is a continuation of Tuesday's lesson - why things float. (So be sure to check out Tuesday's foil boats for a more thorough explanation.) We'll use the same concept to create groovy retro lava cups. Mrs. V is not a big fan of written tests, but what she does love is when students can see a demonstration and explain what's going on. So I'm putting you on the spot of how to explain this project to your kids. I'll be gracious with some hints :) One of my professors of education said his high school students referred to him as 'the benevolent dictator'. I always liked that approach.

Materials needed: glass 3/4 full of water, 1/4 cup vegetable oil, 1 tsp salt, 5 drops of food coloring

It's debatable which is more fun - the actual experiment or the seriously cool food color art in the water!
Pour all the vegetable oil into your colored water. You'll notice that when settled, the oil floats to the top.
Why is this?

Is the vegetable oil more or less dense than water?

Slowly pour salt into the glass. The salt attaches to the oil, creating little pockets of oil and salt. So we've made the oil bubbles to be more dense now than the water. So they.... will...... now...... sink! Right, sink. Watch as the oil bubbles sink. Eventually, the salt will dissolve in the water, leaving the oil bubbles to be once again less dense than water. So they.... will....... now........  float! Again, float. Continue to add salt to achieve lava lamp-like effects.

Color number 2. I think the lighter color made the movement easier to see, although red is fitting for a 'lava' cup.

Oil + Salt > Water

See the movement?

*Special thanks to sciencebob.com for some inspiration behind today's project!