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!