To Sink or not to Sink?

In this lab we will try to figure out why some objects sink and other objects float. Be careful with the water so as not to get your stuff all wet.

We will be using a container with a spout near the top. In your measurements be sure each time to fill the container above the spout and let the overflow go into a larger reservoir for reuse. So you should have enough water in the container so that any object placed in the container will cause water to flow into a graduated cyclinder for measurement.

Part 1: Measure the volume of the aluminum block on your table in units of centimeters cubed (cm^3). Measure the mass of the aluminum block. What is the density of the block? Write down this result. Now prepare the water container for a measurement. Place the graduated cylinder under the spout to catch the water of the overflow. Place the aluminum block in the water and measure the volume of the overflow water. Measure the water level as shown in the drawing. The unit of volume measured with the graduated cylinder is millileters (ml) and one ml is equal to 1 cm^3. What do you observe as far as the volume of the block measured versus the volume of the displaced water? The density of water is 1 g/cm^3 how does this compare to the density of the aluminum block?

Part 2: Now let's examine an object that floats, namely wood. Measure the volume and mass of the piece of wood and record it. Calculate the density of the wood. How does this compare to the density of water? Prepare the container again with water filled up to the top of the spout again. Place the piece of wood in the water. Measure the volume of the displaced water in the graduated cylinder. Now 1 ml of water has a mass of one gram. What is the mass of the displaced water? How does this compare to the mass of the piece of wood?

Part 3: Now let's measure the bouyant force. Using the balance determine the force that the 500 grams mass exerts on it. Record this number, it should be something like 5.6 N. To covert this to dynes which is the unit of force we want add enough zeroes so that there are five places pass the decimal. So the 5.6N becomes 560,000 dynes. Now we want to measure the weight of the water that this 500 gram mass displaces. Again setup the container and spout with the water filled to the top of the spout. Measure the mass of the container which will catch the overflow and call this mE for mass empty. Now place the 500 gram mass in the container and keep it there until the water stops flowing out. Measure on the scale the reading now. Is it lower? Right down the result and again add enough zeroes to have five place past the decimal ie. 4.6 N becomes 460,000 dynes. Subtract this number from the reading you got with the mass hanging in the air. This loss in weight is equal to the buoyant force. Now measure the mass of the container that caught the overaflow and call it mF for mass full. Now how would you get the mass of the diplaced fluid? Calculate the mass of the displaced fluid in the units of grams. Multiply this mass by g (980 g/cm^2) to get the weight of the displaced fluid. How does this number compare with the buoyant force measured above?