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!

Tuesday Teaching {Foil Boats}

Project: Foil Boats

Concept: Displacement

Dictionary.com says: the weight or the volume of fluid displaced  by a floating or submerged body.

 I say for your kiddos: the amount of water that is pushed away by an object

What happens when you get into the bathtub? The water level rises a little. This is because you are taking up space where some of the water used to be. You're replacing the water. An object in water always pushes the water away and takes up that space. This is true for foil boats:

Ok, so we know the water gets pushed aside by an object. Well if all objects replace water, why is it that some objects float and some sink? Well, the simplest answer for your kids is this:

If the green space is heavier than the same amount of water it pushed aside, the object sinks. 

If the green space is lighter than the same amount of water it pushed aside, the object floats.

Think about the tinfoil. The green space of the boat is tinfoil and air, a much lighter combination than water. So the foil boat floats! But as we fill up the green space with more and more weight, the boat becomes heavier than the amount of water it replaced. So eventually, it will sink.

Experiment with different shapes of boats. Have your child brainstorm different kinds of boats they've seen. In my example, I'll show you just two: a sailboat and a raft.

Materials: 'lake', weights (I'm using pennies, but wouldn't it be fun if you had Pirate LEGO men!), foil.

Sailboat foil size (before making the boat): 9 inches x 5.5 inches

Raft foil size (before making the boat): 4.5 inches x 5.5 inches

Be creative with your design. Just make sure you don't have any tears in the foil and that the sides of the boat are at an even height.

How many pennies do you think these boats can hold? Ask your kids and get them thinking.

Let me know how you did! Send a picture and a count and I'll showcase our big winners.

Numbers to beat so far:

Mrs. V - 65 pennies in the sailboat

Mrs. V - 50 pennies in the raft

Holding strong!

And.. sunk.

Raft with pennies - Notice how they're distributed evenly? We want this boat balanced!

And... sunk.

The sunken ships recovered

Extension to this project:
Cardboard Boats. Life-size cardboard boats. This was the highlight of the year for the engineering students. Felix Slade's example here:

Cardboard Boat Race 2010

As always, let me know in the comments if I need to tweak my explanation. Also, I have been generous and loose with the terms here so your kids can make some sense of it. So teach these basics, but if your kids come up with some objects that disprove the theory or they start getting into something above your head, that is awesome!!! There are lots of other principles that affect displacement of an object, so write me a comment and I will teach, teach, teach some more!