Can you make a clay boat float? Key Question Can you make a clay boat float?

Students read the text section FIRST. Leading Questions Why don’t boats made of steel sink? What is Archimedes’ principle? What is meant by the term: “buoyant force”? How can you measure the “buoyant force” acting on an immersed object? Students read the text section FIRST.

Materials and Set up Per Student: ½ to 1 stick of modeling clay Per Group: calculator balance metric ruler 100 mL graduate paper/plastic cup to collect displaced water when FILLING tank 250 mL beaker to collect displaced water when experimenting, dry after each use displacement tank dishpan or shallow bucket for testing clay boats paper towels, sponges, newspaper

Set up your work area Use wax paper to cover work area There is enough clay for each person to build his/her own boat, but we will share non-consumables such as graduated cylinders.

Prediction or Hypothesis? Will the clay sink or float?

Clay Stick Find volume of clay stick in cubic cm.

Density of Clay Find the mass in grams, and then calculate density of clay.

Prediction or Hypothesis? How does the density of your clay compare to water? HINT: Density of pure water = 1 g/cm3

Testing your hypothesis Place clay stick in container of water to see if it floats or sinks. Remove clay quickly and dry it off!

Volume of clay stick in mL Place clay stick carefully into displacement tank. Be sure a dry beaker is under the overflow spout! Use the graduated cylinder to measure the VOLUME of water displaced. How does the volume of displaced water compare to first volume measurement of clay stick?

Floating and Sinking and Forces… Find mass of displaced water. How does this value compare to the volume? Now calculate the WEIGHT of displaced water. (Why calculate weight? Because we want to look at FORCES involved with floating and sinking) Calculate the weight of the stick of clay.

Floating and Sinking and Forces… Find mass of displaced water. How does this value compare to the volume? Now calculate the WEIGHT of displaced water. (Why calculate weight? Because we want to look at FORCES involved with floating and sinking!) Calculate the weight of the stick of clay.

Clay Stick Weight (N) = mass (kg) x 9.8 N/m *Weight (N) = mass (g) x .0098 N/m

Clay Stick Data Summary Weight (N) of object Volume (mL) of displaced water Weight (N) My Stick of Clay 0.58 N 36.0 mL 0.35 N Your Stick ?

Making the clay FLOAT Use the entire stick of clay to mold the clay into a shape that will float. HINT: Think about boats! You will be putting your “boat” in the displacement tank, so be sure that it fits!

Prediction or Hypothesis? How will weight of boat, volume of displaced water, and weight of displaced water compare to the data for the clay stick?

Displacement Use the displacement tank to find out how much water the boat displaces. Measure with the cylinder and record Find the mass of the displaced water. W = mass (g) x .0098 N/m

Conclusions Study the data. What relationships can you see among the measured values?

Thinking about what you observed Did the weight of the clay change during the investigation? Give a reason for your answer. Ans: No, the clay amount was the same. (Unless you lost a little mass to your hands or the water!)

Thinking about what you observed Which displaced more water—the stick of clay or the clay boat, and how much more? Ans: The clay boat displaced MORE than the stick of clay. ______ mL more.

Thinking about what you observed Which weighed more—the stick of clay or the water it displaced, and how much more? Which weighed more—the clay boat or the water it displaced, and how much more?

Thinking about what you observed Ans: The stick of clay wieghed MORE than the water it displaced to the cup. Ans: The clay boat weighed about the SAME as the water it displaced to the cup.

Why a boat floats Use your mass and volume data from Table 2 to calculate the apparent density of your clay boat. This value is called the apparent density because the total volume of the floating boat is NOT displaced. The part of your floating boat that is above the surface isn’t displacing any water.

Apparent Density

Why a boat floats To find out how much of the boat IS below the surface and is displacing water, look at the total amount of water you measured that spilled out into the beaker when the boat was floating.

Apparent Density What other substance has a density very similar to the boat’s apparent density?

Science Connection The interior of the clay boat is filled with air. Some of the air is below the water line. Therefore, both the clay and air were involved in pushing aside, or displacing the water. The boat’s apparent density is less than the water’s density.

Science Connection Archimedes principle states that an object in a fluid is buoyed up by a force equal to the weight of the fluid it displaces. The weight of the object acts downward, and the buoyant force provided by the displaced fluid acts upward. When these two forces are equal, the object floats!

Application

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