1. Gather the Following Materials

Buoyancy Lab Part 1

1. Gather the following materials.

 1 ping pong ball

 1 golf ball

 1 clear plastic cup

 Masking tape

 10 dimes

2. Fill the cup 2/3 full of water. Mark the water level on the cup with a piece of tape.

3. Place the ping pong ball in the water. What happens to the ball? ______

4. Push down on the ball. What do you feel? ______What happens if you quickly let go?______

5. Push down on the ball again until ½ of the ball is under water. Look at the water where you marked the water level with the tape. What happens to the water level?______

6. Tape a dime to the ping pong ball and return it to the water. Does it still float?______

7. Find out how many dimes you need to tape to it before it sinks. Write the number here.______

8. Once the ball is at the bottom of the cup, look at your water level again. Why is it higher than before? ______

9. Write down what you think will happen to the ball and to the water level if you put the golf ball in the cup of water.______

10. Try it.

11. Write down your observations. ______

12. What happened? Why do you think that happened? ______

13. Which of the balls exhibits “positive buoyancy”?______

14. Which of the balls exhibits “negative buoyancy”?______

Scientists working underwater conduct much of their research using scuba gear. Divers use two devices to achieve what is called “neutral buoyancy”. Neutral buoyancy means a diver is neither sinking nor rising to the surface. To achieve this, a diver must take into account several factors :  His/Her weight and percentage of body fat

 The thickness and type of dive suit he/she is using

 The type of air tank he/she is using

 The weight or buoyancy of equipment he/she is carrying

To achieve neutral buoyancy, divers use a weight belt to add weight to themselves and counteract theor tendency to float to the surface. But what if they’re too heavy? Divers also use a buoyancy compensator (or BC) to which they can add air if needed to make them more buoyant.

If you fill a balloon with air and put it underwater, it will rise to the surface. Submarines are full of air. How do they stay underwater? If you put a piece of steel in water, it will sink. Supertankers are made of more than 200,000 tons of steel. How do they float?

Part II

1. Gather the following materials:

 16 paper clips

 Ruler

 Aluminum foil

 A bucket of water

2. Using your ruler to measure, cut 2 squares out of the aluminum foil that measure 8 inches on each side.

3. Wrap 8 of the paper clips with one of the squares of aluminum foil and squeeze it tightly.

4. Place the aluminum foil package containing the paper clips gently on the surface of water in the bucket and let go. What happens? ______

5. Fold the four sides of your other square of aluminum foil up so that it forms a small plate and place the other 8 paper clips into it. 6. Gently place this on the surface of the water and let it go. What happens to this one? ______

7. If the weights are the same between the first piece of foil and the second piece, why did one sink and one float? ______

8. What do you think will happen if you put a small hole in the bottom of the second piece? ______

9. Try it.

10. What happened?______

11. Why do you think that happened?______In 1912, the largest and most luxurious ship ever built set sail on its maiden voyage from Southampton, England, enroute to New York City. Unfortunately, the steel hull of the Titanic was ripped open when it hit the submerged portion of an iceberg. On board were over 2,200 passengers, 1,500 of whom died when the “unsinkable” Titanic sank in the frigid Atlantic Ocean. Icebergs are notoriously hazardous for large boats because 87 percent of their mass lies out of sight below the ocean surface. If a ship does not leave sufficient clearance as it passes and iceberg, it may damage its hull on a submerged ice.

The Titanic was constructed of steel, a carbon alloy of iron approximately 8 times denser than water. It is easy to see how the Titanic could sink once its steel hull was ripped open, but can you explain how it was ever able to float in the first place? Prior to the 3rd century B.C., most people thought it would be impossible for a boat made of iron to float. An iron nail dropped overboard would surely sink, so wouldn’t a large boat made from iron also sink?

Archimedes, a 3rd century B.C. resident of Sicily, is credited with discovering the natural law of buoyancy that proved the common thinking incorrect. Archimedes stated that any object submerged of floating in a fluid is buoyed upward by a force equivalent to the weight of the fluid it displaces. For an object to float, the water must exert an upward force equivalent to the weight of the object. A floating object, therefore, has more force pushing up on it than pushing down. Archemedes suggested that a boat made of iron would float if it was designed to displace (push aside) a volume of water with weight equal to its own. Today, nearly all large commercial ships are made of steel. If these ships were solid, like a nail, they would immediately sink, but because they have hollow hulls, they can float. The largest boat ever to sail, the Hellas Fos of Greece, weighs 611,000 tons. For this giant tanker to float, the ocean must exert an upward force of 611,000 tons to counter its weight. According to Archimedes’ principal, the ocean exerts this force when 611,000 tons of water have been displaced by the boat.

12. The figure above shows that the forces acting on the ship are equal and opposite. The net force is zero and the ship floats. Could a ship displace more water than it weighs?______

13. If you answered yes, explain what would happen to the ship in this case. ______

14. If you answered no, explain why a ship could not displace more water than it weighs. ______Although Archimedes suggested that iron-hulled ships could float, ship builders did not put this idea into practice for approximately 2,000 years. A major turning point in ship construction occurred in 1862, when the Union’s U.S.S. Monitor engaged in battle with the Confederate’s C.S.S. Virginia (Merrimack) in an early battle of the American Civil War. This encounter was the first battle between two iron-clad warships and demonstrated the nautical and strategic value of iron. The battle of the Monitor and the Merrimack helped usher out the days of wooden-hulled ships and usher in the age of steel.

Part 3 In this section, you will try a little buoyancy math. Although Archimedes’ principal applies to all fluids (including gases and liguids), the fluids that divers and shipbuilders are most concerned with are fresh and salt water. It’s necessary to distinguish between the two because an equal volume of each will weigh a different amount. For example, a cubic foot of fresh water weighs approximately 62.4 pounds, but a cubic foot of saltwater weighs approximately 64 pounds. Where does the extra weight come from? If you said the dissolved solids in the saltwater, you’re right!

Lets Look At An Example

Let’s say you have a solid block that has a volume equal to one cubic foot and weighs 63 pounds.

1. If you put it into freshwater, will it sink or float?______

Answer: We know freshwater has a weight of 62.4 pounds per cubic foot. Our block weighs 63 pounds and displaces 62.4 pounds of water. If we subtract 63 from 62.4 we get – 0.6 pounds. This means our block is negatively buoyant and will sink.

2. What if we put the same block in seawater?______

Answer: We know that freshwater has a weight of 62.4 pounds per cubic foot. Again, our block weighs 63 ponds which is less than the weight of the water displaced. If we do the math, we find that 63 pounds from 64 pounds gives us +1 pound. Our block is positively buoyant and will float.

3. If you added one pound of weight to our block and placed it in the saltwater, would it sink or float? ______

Answer: Neither! If we subtract 64 pounds from 64 pounds we get 0 pounds. Our block would be neutrally buoyant and would hover in the water.

Now you try it:

4. A scientist on the ocean floor needs to send a sample of dead coral to the surface to be analyzed. The sample is calculated to weigh roughly 250 pounds and displaces 1.5 cubic feet of water. How big of an airlift bag (in cubic feet) would be required so we could lift this sample to the surface for retrieval?

5. Another scientist is collecting sediment samples from the bottom. He collects 2 cubic feet of sediment that weighs approximately 210 pounds. He also needs to send his samples to the surface for retrieval and has several airlift bags that have a volume of approximately 1 gallon. How many will he need to send his samples to the surface? (Hint: One gallon of seawater weighs about 8 pounds.)