Family Raft Competition
Have you ever floated on a pool toy or wondered why a
boat floats on water? If you have, you’ve experienced the
concept of buoyancy. Buoyancy is the tendency of an object
to float when placed in a liquid. The liquid exerts an upward
force on the object. If the objects density is low enough, it
will float but if its density is too high the object sinks.
In this family activity you will design and test a raft made using
drinking straws and foil.
Materials: 6-8 drinking straws per family member or team
Aluminum foil (make sure to get an adult to help cut this)
Pennies
Process
1. Make sure each team or family member receives the same amount of straws and foil.
2. Take a few minutes to decide how you will construct your raft prior to starting. (You may want to
read about rafts on the internet before beginning).
3. Create a sketch of how your raft will look when completed.
4. Construct your raft.
5. Fill a sink or bathtub with enough water to create a “lake” for testing your raft.
6. Carefully float your raft on the surface of the water.
7. Slowly add pennies, one at a time, to the top of your raft. Keep in mind that the density of an
object is based upon how much mass it has and how much space it fills (volume). You may want
to experiment with making a stack of pennies in the middle versus spreading them out evenly
across the top of the raft.
8. The winner’s raft is the one that can hold the most pennies without sinking.
Something to Think About:
1. Did your raft hold more pennies when they were spread out over the surface of the raft or
stacked in the middle?
2. Is density lower when all the mass of the pennies is concentrated in the middle of the raft or
when spread out over the surface of the raft?
3. How could you change your design to make a raft that could hold even more pennies?