## Ship Shape

Skills
communicating
observing
comparing
applying

Materials
aluminum foil
ruler
scissors
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
water

Doing the Activity
1. Measure and cut aluminum foil to make two 10x10 cm (4x4 inch) squares.
2. Using a piece of foil, design a floating object that can carry cargo. Your design can be any shape. Be creative!
3. 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 or interesting.
4. 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.
5. Put marbles, beans, or pennies in a paper cup. The marbles, beans, or pennies will be your test cargo for your floating object.
6. 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 it.
7. Remove your object and cargo from the water. Place all of the cargo back into the cup.
8. Using what you learned from your first vessel, design a new object with the other piece of foil. Try a different shape!
9. Predict whether it will take more or less cargo to sink your new design.
10. 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 the water?
• What happened to each of your objects as you added cargo? Why?
• 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 object.
• Compare the design differences of these boats and ships. Why do they have different designs?
 canoe cruise ship barge sail boat freighter supertanker row boat speed boat
• 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 work.
• 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 find out!

Activity Source
"Funtivities: Hands-on Science and Math." Iowa State University Program for Women in Science and Engineering. Extension Distribution Center