Question.3700 - Density Lab Oceanography 101Names: Michael Powdrill Objectives Learn about how density is measured Learn how densities of materials relate to their behavior when mixed together Why do objects that are the same size sometimes have different weights? The answer has to do with the objects density. A rock and cork of equal size will have the same volume, but which one will be heavier? The rock. Why? Because the rock has more mass. So even though the rock and cork have the same volume, the rock is denser than the cork. The rock has more mass in the same volume. This is due to the atomic structure of the chemical elements that it is made up of. Mass is a measure of the amount of matter in an object. The gram is a unit of mass. We will measure mass with a scale or balance. Volume is a measure of how much space an object takes up. Units of volume include cubic centimeters (cm3) or milliliters (mL). Volume can be determined by measuring the dimensions of an object, such as a cube, and multiplying: Volume of a cube (cm3) = width (cm) x height (cm) x length (cm). Using the equation above, determine the volume of a cube that measures 3 cm wide, 3 cm tall, and 3 cm long. Volume: 3?3?3=27cm3 Lets say this cube is made out of ice and has a mass of 24.76 grams (g). What is this ice cubes density? Density = mass / volume = 24.6 g / 27 cm3 = 0.917 g/cm3 The density of liquid water is slightly higher than that of frozen water ice. Liquid waters density at standard pressures and temperatures is 1.00 grams per cubic centimeter (g/cm3). Given that density, what is the mass of a cube of water measuring 3 cm wide, 3 cm tall, and 3 cm long? Mass = 1.00 ? 27 = 27g Compare the weight of the water you calculated in question 1.3 with the weight of the ice of the same volume given in question 1.2. Which is heavier, the liquid water or the ice? Notice that the cube of water is the same size (or volume) as the cube of ice. Based on the observation, since 27 g (liquid water) is greater than 24.76 g (ice), the liquid water is heavier than the ice of the same volume. You know that ice floats on water. Explain why. Because the density is lower around 0.917 g/cm? than that of liquid water, 1.00 g/cm?, ice tends to float with lower density than water will. Measuring volume by measuring the dimensions of an object works well for things that are easy to measure, like cubes, but it does not work well for irregularly shaped objects like rocks or shells. So there is another relatively simple method for measuring volume for oddly shaped things. Simply put, you fully submerge the object in water in a type of container (a graduated cylinder ) where you can measure how much the water level rises once the object is submerged. 784204853226Volume after submerged volume before submerged = volume of object Volume after submerged volume before submerged = volume of object Density is a measure of the mass per unit volume. In other words, it tells us how much matter is contained in the space an object takes up. Units of density are in grams per centimeter cubed (g/cm3). Density relationships structure our entire world, from the ground underneath to the air above. In future labs, we will use density to understand the structure of ocean water, thermohaline circulation in the ocean, and movement of air in the atmosphere. The following questions use a simulation for you to learn more about density. To answer the questions, visit the simulation on the PBS Density Simulation website. Note: 1 milliliter = 1 mL = 1 cubic centimeter = 1 cc or 1 cm3, so when measuring volume in mL it is the same as cm3 To begin, click the button at the top to turn the fluid into water. What is the fluid density of pure water? What is the volume of water in the beaker when there is nothing else in it? You may need to hit reset and look at the volume in the beaker before the object falls into the beaker. You can also drag the object out of the beaker and put it on the scale. Use the slider bars below the beaker to adjust mass and volume one at a time. At any time, you may drag the object out of the beaker and put on the balance to measure its mass. Describe what happens when you adjust the mass of the object. Does it change size? How do you think this affects its density? Did the object sink or float higher? What happened to the water level in the beaker? When I increased its mass the object does not change size, but as the mass increases while the?volume remains constant, the density increases, also as the mass increases the object sinks lower, and the water level in the beaker rises. When I decreased its mass the size remains unchanged with a drop in density and it starts floating higher in the water, and the water level lowers. Describe what happens when you adjust the volume of the object. Does it get heavier? How do you think this affects its density? Did the object sink or float higher? How can you relate that to observed changes to the fluid in the beaker? When I (we) increased its volume, it becomes larger, but if mass stays the same, density decreases while it floats higher in the water, causing the water level to rise less compared to an object with higher density. When I (we) decrease its volume, it becomes smaller and in scenario if mass remains constant, density increases; also, there is a possibility that the?object sinks lower, and the water level rises more as it displaces more water for its size. On the bottom right side of your screen click on the name of different materials. A new block will materialize. Record the mass and volume for each object in the table below. Then use those values to calculate its density. Please show your calculations. To measure volume, Volume = beaker level when object is submerged beaker level with no object If your object floats, decrease the fluid density until it sinks to measure its volume. Material Mass (g) Volume (mL) Density (g/cm3) Gold 40.53 gms 27.6 1.469 g/cm3 Lead 72.32 gms 31.9 2.267 g/cm3 Foam 2.76 gms 26.7 0.103 g/cm3 Iron 31.48 gms 29.5 1.067 g/cm3 Wood 1.95 gms 26.3 0.074 g/cm3 Ice 9.2 gms 29.2 0.315 g/cm3 Rubber 0.52 gms 25.7 0.020 g/cm3 Mystery ??? 18.58 gms 31.2 0.596 g/cm3 Based on its density, name 2 things that the mystery material could be. (Look it up here https://www.engineeringtoolbox.com/density-solids-d_1265.html. Note that 1kg/m3 is the same as 1g/ml or 1g/cm3) Pine wood (density around 0.5-0.6 g/cm?) Cork (density around 0.24-0.6 g/cm?) Rank the objects from least dense to most dense in the table below. Use the density values determined above to arrange them from least dense to most dense. Qualitative comparison Material Density (g/cm3) (copied from table above) Did the object float or sink in water (when the fluid density was 1 g/mL)? yes or no LEAST DENSE 352425167580 MOST DENSE Rubber 0.020 Floats Wood 0.074 Floats Foam 0.103 Floats Ice 0.315 Floats Mystery Material 0.596 Floats Iron 1.067 Sinks Gold 1.469 Sinks Lead 2.267 Sinks Use the observations in the tables above and the density of water to describe how you would use density to predict whether an object will float or sink in water. Because water's density is 1 g/cm? anything denser than water displaces less volume and sinks, while less dense objects displace more volume and float; so any object with lesser density than 1 g/cm3 will be subjected to floating in water that possesses density great than 1 g/cm3 Make predictions using what you have learned about density. Which is denser, salt water or fresh water? Based on your answer, explain what happens as rivers flow into the sea. Salt water contains dissolved salt making it denser than fresh water when river flows in to the sea the less dense fresh water flows over top of more dense salt water until equilibrium is attained Which is denser, hot water or cold water? Based on your answer, explain where the coldest water in the ocean would be. Cold water tends to be more dense than hot water which is why it is found at the deepest level in the ocean since it sinks
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