September 2014

Float Your Boat (9/3/14)

MATERIALS:

  • Large bowl or container
  • Water
  • Aluminum foil
  • Ruler
  • Scissors
  • Pennies

INSTRUCTIONS:

  1. Fill up the container with water.
  2. Using your ruler, cut two 6-inch squares of aluminum foil.
  3. Wrap one of the aluminum foil squares around 10 pennies, and roll the foil into a tight ball.
  4. Drop the aluminum foil ball into the water. What happens?
  5. Now for the challenge! Use the remaining aluminum foil square to design your own boat. Does your boat float in the water?
  6. If your boat is seaworthy, estimate how many pennies your boat can hold. Add pennies one at a time. Was your estimate right?

HOW DOES IT WORK?

When you place the boat in the water, it floats because its density is less than the density of water. When you add cargo (pennies) to the boat, the density of the boat will increase. Eventually, when enough pennies are added, the boat’s density roughly equals the water’s. This happens right before the penny that sinks the boat is added. The boat sinks because its density has finally become greater than the density of water.

NOW TRY THIS!

  • Try making boats in different shapes and sizes. What shape holds the most cargo?
  • If you add salt to the water, will your boat hold more pennies?

Floating Lemons and Sinking Limes 

MATERIALS:

  • Lemons and limes that are roughly the same size and weight
  • Deep container
  • Water

INSTRUCTIONS:

  1. Fill up the container with water, and toss in the lemons. Do they float or sink? The lemons should be floating on the surface of the water.
  2. Now drop in the limes! Do they float or sink? You may find the occasional floating lime, but most of them will sink to the bottom.
  3. Why does this happen? If the lemons and limes are about the same size and weight, shouldn’t they both sink or float? Maybe the rind has something to do with it! Carefully peel the rind off of the fruit.
  4. Drop the freshly peeled lemons and limes into the water. What happens now?

HOW DOES IT WORK?

The density of water is 1 g/mL. The density of a lemon is less than or equal to the density of water. If you calculate the density (density = mass/volume) of a lemon and a lime that are equal in weight, you will find that the lime is a little more dense than the lemon. That’s why lemons float and limes sink!

NOW TRY THIS!

  • Cut the fruit into slices. Does this change your results?
  • Try experimenting with other fruits and vegetables!