- aluminum foil
- 15-25 marbles or 225 g (1/2 pound) dry beans
- 50 pennies (optional)
- paper cups to hold marbles, dry beans or pennies
- bucket or plastic tub large enough to hold more than
1-2 liters (1-2 quarts) of water
- paper towels
- Doing the Activity
- Measure and cut aluminum foil to make two 10x10 cm
(4x4 inch) squares.
- Using a piece of foil, design a floating object that
can carry cargo. Your design can be any shape. Be
- Sketch a picture of the object you created or write a
short description of it on the chart on the next page.
Include in your sketch or description information about
its shape, size, and anything else you think is important
- Place your object in a bucket or plastic tub half
filled with water. Does your object float? Observe how
deep your object sits in the water.
- Put marbles, beans, or pennies in a paper cup. The
marbles, beans, or pennies will be your test cargo for
your floating object.
- Test how much cargo your object will support before
it sinks! Place one piece of cargo on your object.
Continue adding cargo, one piece at a time, until your
object sinks. Record on the chart the kind of cargo you
used and the number of cargo pieces needed to sink
- Remove your object and cargo from the water. Place
all of the cargo back into the cup.
- Using what you learned from your first vessel, design
a new object with the other piece of foil. Try a
- Predict whether it will take more or less cargo to
sink your new design.
- Test your prediction! Repeat steps 3, 4, 6, and 7
using your second foil object.
- Talking it over
- Before you added any cargo of marbles, beans, or
pennies, which of the objects you designed sat lowest in
- What happened to each of your objects as you added
- Compare the amount of cargo supported by each of your
objects. Which object supported the most cargo? Why?
- Discuss what happened to the water level in the
bucket or tub when you added more cargo to your floating
- Compare the design differences of these boats and
ships. Why do they have different designs?
- Have you ever seen or used a kick board or life
preserver at a swimming pool? Have you ever seen or worn
a life jacket on a boat? Discuss how these objects
- How does a submarine adjust its density so that it
can dive or surface?
- What's Happening
- Experiment with variables that affect density and
change the ability of an object to float.
- In ancient Greece, a king had a goldsmith make him a
new crown. When the crown arrived, the king was
suspicious that the goldsmith had cheated him and had not
made the crown out of solid gold. The king asked
Archimedes, a very knowledgeable man, to find out if the
crown was made of pure gold without destroying the crown
to do it. According to legend, while Archimedes was
thinking about how to solve this problem, he took a bath.
He noticed that when he stepped into the full tub, some
of the water spilled out. It occurred to him that the
volume of this water must be the same as the volume of
his body. "Eureka!" he shouted, which means "I've found
it!" in Greek. Archimedes got a bar of silver and a bar
of gold. Each bar had the same mass as the crown. He
placed the silver bar in the water and observed the level
of the water. Next, he measured how much water the gold
bar displaced, or pushed aside. Then he put the
crown in the water. The crown displaced less water than
the gold bar and more than the silver bar. He knew that
the crown was not made of pure gold. The goldsmith had
cheated the king!
- Any object placed in a fluid, such as water,
will displace some of the fluid. What happens to the
water level when you put more dishes in a sink of water?
The dishes displace some of the water, causing the water
level in the sink to rise. This happens because the
dishes and the water can not occupy the same space at the
same time. Any object placed in a fluid will displace a
volume of the fluid. The volume of fluid displaced equals
the volume of the object that sinks below the surface of
the fluid. So, why does a golf ball sink and a ping pong
ball float? Why does a brick sink and a block of wood
that is the same size as the brick float? Whether an
object will sink or float in a fluid depends on two
factors: density--mass divided by volume--and
buoyancy. Buoyancy is the force of the fluid
pushing up on an object as the object pushes down on the
fluid. If the mass of the fluid pushed aside by the
object is the same as, or less than, the mass of the
object, the object floats. The object cannot sink any
further because of the buoyant force. Buoyancy depends on
the object's volume.
- More Challenges
- How does changing an object's volume change buoyancy?
What happens if you change the mass of the object? Let's
- Activity Source
- "Funtivities: Hands-on Science and Math." Iowa State
University Program for Women in Science and Engineering.
Extension Distribution Center
(515) 294-5247, order # 4H-952 for grades 4-5, #4H-952LDR
for grades 4-5 leader's guide, #4H-953 for grades 6-8,
#4H-953LDR for grades 6-8 leader's guide.